U.S. patent application number 10/973749 was filed with the patent office on 2005-04-21 for nonradiative dielectric waveguide and a millimeter-wave transmitting/receiving apparatus.
This patent application is currently assigned to KYOCERA CORPORATION. Invention is credited to Hayata, Kazuki, Hiramatsu, Nobuki, Kii, Hironori, Okamura, Takeshi, Sato, Akinori, Terashi, Yoshitake, Uchimura, Hiroshi.
Application Number | 20050085209 10/973749 |
Document ID | / |
Family ID | 27554468 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050085209 |
Kind Code |
A1 |
Hiramatsu, Nobuki ; et
al. |
April 21, 2005 |
Nonradiative dielectric waveguide and a millimeter-wave
transmitting/receiving apparatus
Abstract
A NRD guide includes a pair of parallel plate conductors opposed
to each other at a spacing equal to or shorter than half the
wavelength of a high-frequency signal to be transmitted and having
opposing inner surfaces whose arithmetic average roughness Ra
satisfies 0.1 .mu.m.ltoreq.Ra.ltoreq.50 .mu.m, and a dielectric
strip arranged between the pair of parallel plate conductors and
held in contact with the respective inner surfaces of the parallel
plate conductors. The dielectric strip is strongly secured to the
inner surfaces to exhibit an excellent durability. The transmission
loss of the high-frequency signal can be effectively
suppressed.
Inventors: |
Hiramatsu, Nobuki;
(Seika-cho, JP) ; Okamura, Takeshi; (Nara-shi,
JP) ; Hayata, Kazuki; (Uji-shi, JP) ; Terashi,
Yoshitake; (Kagoshima-shi, JP) ; Kii, Hironori;
(Seika-cho, JP) ; Uchimura, Hiroshi;
(Kagoshima-shi, JP) ; Sato, Akinori; (Hayato-cho,
JP) |
Correspondence
Address: |
HOGAN & HARTSON L.L.P.
500 S. GRAND AVENUE
SUITE 1900
LOS ANGELES
CA
90071-2611
US
|
Assignee: |
KYOCERA CORPORATION
|
Family ID: |
27554468 |
Appl. No.: |
10/973749 |
Filed: |
October 26, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10973749 |
Oct 26, 2004 |
|
|
|
09689547 |
Oct 12, 2000 |
|
|
|
6832081 |
|
|
|
|
Current U.S.
Class: |
455/328 ;
333/135; 333/251 |
Current CPC
Class: |
H01P 3/165 20130101;
H01Q 13/28 20130101 |
Class at
Publication: |
455/328 ;
333/251; 333/135 |
International
Class: |
H04B 001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 1999 |
JP |
11-291033(PAT.) |
Nov 30, 1999 |
JP |
11-339887(PAT.) |
Dec 15, 1999 |
JP |
11-356318(PAT.) |
Jan 20, 2000 |
JP |
2000-14200(PAT.) |
Jan 26, 2000 |
JP |
2000-21824(PAT.) |
Jan 31, 2000 |
JP |
2000-27289(PAT.) |
Claims
1-21. (canceled)
22. A millimeter wave transmitting/receiving apparatus, comprising:
a pair of parallel plate conductors opposed to each other at a
spacing equal to or shorter than half the wavelength of a
high-frequency signal to be transmitted; a circulator made of two
ferromagnetic plates provided between the pair of parallel plate
conductors and opposed to each other in the same direction as the
pair of parallel plate conductors being spaced apart; a first
dielectric strip arranged between the pair of parallel plate
conductors; a millimeter wave signal oscillator provided at one end
of the first dielectric strip for outputting a millimeter wave
signal to be transmitted; a second dielectric strip connected with
the one end of the first dielectric strip and radially arranged
with respect to the circulator between the pair of parallel plate
conductors; a third dielectric strip radially arranged with respect
to the circulator between the pair of parallel plate conductors and
having a transmitting/receiving antenna at its leading end; a
fourth dielectric strip radially arranged with respect to the
circulator between the pair of parallel plate conductors; first,
second, third and fourth suppressors arranged between the one end
of the first dielectric strip and the millimeter wave signal
oscillator and between the second, third and fourth dielectric
strips and the circulator, and formed by arranging a plurality of
conductive layers at specified intervals in a plane parallel to a
transmission direction of a high-frequency signal inside the ends
of the respective dielectric strips; and a mixer for mixing part of
the millimeter wave signal outputted from the millimeter wave
signal oscillator and a radio wave received by the
transmitting/receiving antenna to generate an
intermediate-frequency signal by coupling an intermediate position
of the first dielectric strip and that of the fourth dielectric
strip to each other.
23. A millimeter wave transmitting/receiving apparatus according to
claim 22, wherein a dimension of each conductive layer along the
transmission direction is equal to or shorter than half the
wavelength of a TEM mode electromagnetic wave of the high-frequency
signal, and a thickness thereof is 0.1 mm or smaller.
24. A millimeter wave transmitting/receiving apparatus, comprising:
a pair of parallel plate conductors opposed to each other at a
spacing equal to or shorter than half the wavelength of a
high-frequency signal to be transmitted; a circulator made of two
ferromagnetic plates provided between the pair of parallel plate
conductors and opposed to each other in the same direction as the
pair of parallel plate conductors being spaced apart; a first
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a millimeter wave
signal oscillator provided at one end of the first dielectric strip
for outputting a millimeter wave signal to be transmitted; a second
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors and having a
transmitting antenna at its leading end; a third dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors; first, second, third and fourth
suppressors arranged between one end of the first dielectric strip
and the millimeter wave signal oscillator and between the first,
second and third dielectric strips and the circulator, and formed
by arranging a plurality of conductive layers at specified
intervals in a plane parallel to a transmission direction of a
high-frequency signal inside the ends of the respective dielectric
strips; a fourth dielectric strip having one end connected with the
first or second dielectric strip between the pair of parallel plate
conductors for transmitting part of the millimeter wave signal
outputted from the millimeter wave signal oscillator; a fifth
dielectric strip arranged between the pair of parallel plate
conductors and having a receiving antenna at its leading end; and a
mixer for mixing part of the millimeter wave signal outputted from
the millimeter wave signal oscillator and a radio wave received by
the receiving antenna to generate an intermediate-frequency signal
by coupling an intermediate position of the fourth dielectric strip
and that of the fifth dielectric strip to each other.
25. A millimeter wave transmitting/receiving apparatus according to
claim 24, wherein a dimension of each conductive layer along the
transmission direction is equal to or shorter than half the
wavelength of a TEM mode electromagnetic wave of the high-frequency
signal, and a thickness thereof is 0.1 mm or smaller.
26. A millimeter wave transmitting/receiving apparatus, comprising:
a pair of parallel plate conductors opposed to each other at a
spacing equal to or shorter than half the wavelength of a
millimeter wave signal to be transmitted; a circulator made of two
ferromagnetic plates provided between the pair of parallel plate
conductors and opposed to each other in the same direction as the
pair of parallel plate conductors being spaced apart; a first
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a millimeter wave
signal oscillator provided at one end of the second dielectric
strip for outputting the millimeter wave signal to be transmitted;
a second dielectric strip radially arranged with respect to the
circulator between the pair of parallel plate conductors, and
having a transmitting/receiving antenna at it leading end; a third
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a fourth dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors, and having one end connected
with the first dielectric strip; first, second and third
suppressors arranged between the first, second and third dielectric
strips and the circulator for suppressing electromagnetic waves of
unnecessary modes; first, second and third impedance matching
members arranged at the end faces of the first, second and third
suppressors toward the circulator and having a relative dielectric
constant different from that of the first, second and third
dielectric strips; and a mixer for mixing part of the millimeter
wave signal outputted from the millimeter wave signal oscillator
and having transmitted in the fourth dielectric strip and a radio
wave received by the transmitting/receiving antenna to generate an
intermediate-frequency signal and transmitted in the third
dielectric strip by coupling an intermediate position of the third
dielectric strip and that of the fourth dielectric strip to each
other.
27. A millimeter wave transmitting/receiving apparatus according to
claim 26, wherein the impedance matching members are formed at
their sides toward the respective parallel plate conductors with
stepped portions having a height substantially equal to the
thickness of the respective ferromagnetic plates forming the
circulator, and the impedance matching members and the circulator
are connected by holding the impedance matching members by the two
ferromagnetic plates at the stepped portions.
28. A millimeter wave transmitting/receiving apparatus, comprising:
a pair of parallel plate conductors opposed to each other at a
spacing equal to or shorter than half the wavelength of a
millimeter wave signal to be transmitted; a circulator made of two
ferromagnetic plates provided between the pair of parallel plate
conductors and opposed to each other in the same direction as the
pair of parallel plate conductors being spaced apart; a first
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a millimeter wave
signal oscillator provided at one end of the first dielectric strip
for outputting the millimeter wave signal to be transmitted; a
second dielectric strip radially arranged with respect to the
circulator between the pair of parallel plate conductors and having
a transmitting antenna at its leading end; a third dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors; first, second and third suppressors
arranged between the first, second, and third dielectric strips and
the circulator for suppressing electromagnetic waves of unnecessary
modes; first, second and third impedance matching members arranged
at the end faces of the first, second and third suppressors toward
the circulator and having a relative dielectric constant different
from that of the second, third and fourth dielectric strips; a
fourth dielectric strip having one end connected with the first
dielectric strip between the pair of parallel plate conductors for
transmitting part of the millimeter wave signal outputted from the
millimeter wave signal oscillator; a fifth dielectric strip
arranged between the pair of parallel plate conductors and having a
receiving antenna at its leading end; and a mixer for mixing part
of the millimeter wave signal outputted from the millimeter wave
signal oscillator and a radio wave received by the receiving
antenna to generate an intermediate-frequency signal by coupling an
intermediate position of the fourth dielectric strip and that of
the fifth dielectric strip to each other.
29. A millimeter wave transmitting/receiving apparatus according to
claim 28, wherein the impedance matching members are formed at
their sides toward the respective parallel plate conductors with
stepped portions having a height substantially equal to the
thickness of the respective ferromagnetic plates forming the
circulator, and the impedance matching members and the circulator
are connected by holding the impedance matching members by the two
ferromagnetic plates at the stepped portions.
30. A millimeter wave transmitting/receiving apparatus, comprising:
a pair of parallel plate conductors opposed to each other at a
spacing equal to or shorter than half the wavelength of a
millimeter wave signal to be transmitted; a circulator made of two
ferromagnetic plates provided between the pair of parallel plate
conductors and opposed to each other in the same direction as the
pair of parallel plate conductors being spaced apart; a first
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a millimeter wave
signal oscillator provided at one end of the first dielectric strip
for outputting the millimeter wave signal to be transmitted; a
second dielectric strip radially arranged with respect to the
circulator between the pair of parallel plate conductors; a third
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a fourth dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors; a metallic waveguide having an
open termination at one end connected with an opening formed in at
least one of the pair of parallel plate conductors in a position
corresponding to where the electric field of a standing wave of IBM
mode transmitting in the third dielectric strip is at maximum while
having an open termination at the other end provided with a
transmitting/receiving antenna; a mixer for mixing part of the
millimeter wave signal from the millimeter wave signal oscillator
having transmitted in the fourth dielectric strip and a radio wave
having transmitted in the third dielectric strip and received by
the transmitting/receiving antenna to generate an
intermediate-frequency signal by coupling an intermediate position
of the third dielectric strip and that of the fourth dielectric
strip to each other.
31. A millimeter wave transmitting/receiving apparatus, comprising:
a pair of parallel plate conductors opposed to each other at a
spacing equal to or shorter than half the wavelength of a
millimeter wave signal to be transmitted; a circulator made of two
ferromagnetic plates provided between the pair of parallel plate
conductors and opposed to each other in the same direction as the
pair of parallel plate conductors being spaced apart; a first
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a millimeter wave
signal oscillator provided at one end of the second dielectric
strip for outputting the millimeter wave signal to be transmitted;
a second dielectric strip radially arranged with respect to the
circulator between the pair of parallel plate conductors; a third
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a fourth dielectric
strip having one end connected with the first dielectric strip
between the pair of parallel plate conductors for transmitting part
of the millimeter wave signal outputted from the millimeter wave
signal oscillator; a fifth dielectric strip arranged between the
pair of parallel plate conductors; a first metallic waveguide
having an open termination at one end connected with an opening
formed in at least one of the pair of parallel plate conductors in
a position corresponding to where the electric field of a standing
wave of LSM mode transmitting in the second dielectric strip is at
maximum while having an open termination at the other end provided
with a transmitting antenna; a second metallic waveguide having an
open termination at one end connected with an opening formed in at
least one of the pair of parallel plate conductors in a position
corresponding to where the electric field of a standing wave of LSM
mode transmitting in the fifth dielectric strip is at maximum while
having an open termination at the other end provided with a
receiving antenna; and a mixer for mixing part of the millimeter
wave signal outputted from the millimeter wave signal oscillator
and a radio wave received by the receiving antenna to generate an
intermediate-frequency signal by coupling an intermediate position
of the fourth dielectric strip and that of the fifth dielectric
strip to each other.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a nonradiative dielectric
waveguide used in a high frequency band of, e.g., millimeter-waves
and a millimeter wave transmitting/receiving apparatus using such a
nonradiative dielectric waveguide.
[0002] A first construction example of a conventional nonradiative
dielectric waveguide is described with reference to FIG. 34. In the
following, the nonradiative dielectric waveguide is referred to as
an NRD guide. The NRD guide shown in FIG. 34 is constructed by
providing a dielectric strip 703 between a pair of parallel plate
conductors 701, 702 whose spacing is .lambda./2 or shorter when a
wavelength of an electromagnetic wave (high-frequency wave)
propagating in the air at an operating frequency is .lambda., and
is based on such an operation principle that the electromagnetic
wave transmits along the dielectric strip 703, and radiation of the
transmitting wave is suppressed by the blocking effect of the
parallel plate conductors 701, 702. In FIG. 34, the upper parallel
plate conductor 701 is partly cut away so as to make the inside
visible.
[0003] The NRD guide according to the first conventional
construction example may include a curved dielectric strip 704
between the pair of parallel plate conductors 701 and 702. Such a
construction enables an electromagnetic wave to easily be
transmitted in a curved manner and has advantages of
miniaturization of a millimeter wave integrated circuit and a
circuit design with a higher degree of freedom. In FIG. 35, the
upper parallel plate conductor 702 is shown in broken line so as to
make the inside visible.
[0004] There are known two modes, i.e., an LSM (longitudinal
section magnetic) mode and an LSE (longitudinal section electric)
mode as millimeter wave transmission mode of the NRD guides. The
LSM mode having a smaller loss is generally used. Since the
parallel plate conductors 701, 702 of the conventional NRD guides
need to have a high electric conductivity and an excellent
processability, conductor plates formed of Cu, Al, Fe, SUS
(stainless steel), Ag, Au, Pt or like metallic material have been
used. Alternatively, insulating plates made of ceramics or resin
having a conductive layer made of the above metallic material
formed on the outer surface have also been used.
[0005] Teflon (trademark of polytetrafluoroethylene), polystyrene
and like resin material having a relative dielectric constant of 2
to 4 have been used for the dielectric strips 703, 704 due to their
good processability. The dielectric strips 703, 704 have been
secured to the parallel plate conductors 701, 702 by an
adhesive.
[0006] However, if the NRD guide is constructed by the dielectric
strip formed of the conventionally used Teflon, polystyrene or
dielectric material having a relative dielectric constant of 2 to 4
in the first conventional construction example, there is a problem
that a steeply curved portion cannot be provided because of a bend
loss and a large transmission loss at a joining portion of the
dielectric strip. Even if a moderately curved portion could be
provided, a radius of curvature of the curved portion would need to
be precisely determined. However, there is a restriction in
precisely setting the radius of curvature if the dielectric strip
is made of Teflon, polystyrene or like material.
[0007] Further, a bend loss at the curved portion can be suppressed
to a practically negligible level by strictly specifying a
curvature of the dielectric strip in conformity with the operating
frequency. However, the bend loss increases upon even a slight
shift of the operating frequency. For instance, if an attempt is
made to reduce a bend loss at and near 60 GHz, a width of its
permissible range is only about 1 to 2 GHz. This is because, in the
case that the NRD guide is formed using a dielectric material
having a relative dielectric constant of 2 to 4, part of the
millimeter wave of the LSM mode is converted at a curved portion
thereof into that of the LSE mode to increase a loss because
distribution curves of the LSM mode and the LSE mode are very
approximate to each other.
[0008] In the case that a high-frequency device, a high-frequency
circuit module or the like is fabricated using the NRD guide having
the dielectric strips 703, 704 made of an inorganic compound such
as ceramics, it is possible to provide a steeply curved portion at
the dielectric strips 703, 704, but not possible to provide a high
bending dimensional precision. Thus, it has been difficult to
fabricate such a complicated configuration comprised of a plurality
of linear and curved portions. There is an additional problem of
breaking or damaging the dielectric strips 703, 704 due to a
difference in thermal expansion coefficient between the parallel
plate conductors 701, 702 and the dielectric strips 703, 704, an
impact, and other factors.
[0009] Further, it has been difficult to suppress a transmission
loss of a high-frequency signal to or below a specified value in
any of the NRD guides according the first conventional
construction.
[0010] Next, a second construction example of the conventional NRD
guide is described. The NRD guide of the second construction
example is constructed, as disclosed in Japanese Unexamined Patent
Publication No. 8-65015, such that a dielectric strip is provided
between a pair of parallel plate conductors, two small projections
are formed on the dielectric strip, and recesses engageable with
the small projections are formed in one of the parallel plate
conductors. In the thus constructed NRD guide, the parallel plate
conductors and the dielectric strip can be precisely positioned
with respect to each other by fitting the small projections into
the recesses.
[0011] Other construction examples in which the parallel plate
conductors and the dielectric strip are precisely positioned with
respect to each other include those disclosed in Japanese
Unexamined Patent Publication Nos. 6-260824 and 9-64608.
Specifically, these publications disclose that a dielectric member
is made of a strip section and collars formed on the upper and
lower surfaces of the strip section to prevent a displacement of
the strip section, and parallel plate conductors are formed by
applying plating of, e.g., copper, silver or a silver paste to the
upper and lower surfaces of the dielectric member and baking
it.
[0012] In the NRD guides of this type, resin materials having a
relative dielectric constant of 2 to 4 such as Teflon and
polystyrene as mentioned above and ceramic materials such as
alumina and cordierite are frequently used as the material of the
dielectric strips. Since the dielectric strips need to be precisely
positioned, the dielectric strips and the parallel plate conductors
are adhered by using an epoxy resin or an organic adhesive having a
high heat resistance such as a polyimide resin or a BT resin as
disclosed in Japanese Unexamined Patent Publication No. 10-163712.
In the case that positioning is not sufficiently precise by the
above adhesion, the construction disclosed in Japanese Unexamined
Patent Publication No. 8-65015 is adopted.
[0013] In the second conventional construction example in which the
small projections of the dielectric strip are fitted into the
recesses of the parallel plate conductor, it is impossible to
arrange the dielectric strip unless the positions of the small
projections and the recesses agree. Even if the positions of the
small projections and the recesses agree, it is difficult to
precisely position the dielectric strip if the small projections
are too small or the recesses are too large. This disadvantageously
increases a transmission loss of a signal in a coupler formed by
bringing connecting portions with the respective devices such as
diodes, circulators, terminators closer to the dielectric
strip.
[0014] In the NRD guide in which the dielectric member is comprised
of the strip section and the collar portions, it is difficult to
process the same with a good dimensional precision, and a separate
housing or the like needs to be provided since the parallel plate
conductors formed by baking the plating or silver paste have a low
strength. The NRD guides in which the adhesive made of an epoxy
resin is used have a low reliability when being used in a severe
environment because the epoxy resin has a low heat resistance,
whereas those in which the adhesive made of a polyimide resin or BT
resin is used have a problem of deterioration with time when being
exposed to a severe environment.
[0015] It has been also difficult to suppress a transmission loss
of a high-frequency signal to or below a specified value in any of
the NRD guides according the second conventional construction.
[0016] Next, a third construction example of the conventional NRD
guide is described. The NRD guide of the third construction example
is constructed such that a mode suppressor is provided at an end of
a dielectric strip provided between a pair of parallel plate
conductors by providing a conductive layer inside the dielectric
strip. More specifically, an operation mode of the NRD guide is
generally an LSM mode. However, the NRD guide is sometimes
connected with a circulator, an oscillator or like device in
designing a circuit, and an LSE mode occurs at a connecting portion
with the circulator, the oscillator or the like device. An LSE mode
suppressor is provided between the NRD guide and the other circuit
device in order to suppress the transmission of the LSE mode.
[0017] In such NRD guides, resin materials having a relative
dielectric constant of 2 to 4 such as Teflon and polystyrene are
frequently used as the material of the dielectric strips. Known
mode suppressors are formed by splitting the dielectric strip into
two half pieces, printing a conductive layer of a specified shape
on one surface of one half piece, and placing the other piece next
to a conductive layer surface of the one half piece where the
conductive layer is formed, or securing the conductive layer
surface of the one half piece to the other half piece by an
adhesive.
[0018] Japanese Unexamined Patent Publication No. 63-185101
discloses a mode suppressor obtained by forming a metal plate of a
specified shape and integrally molding this metal plate and a
dielectric strip made of a polystyrene or like material.
[0019] However, in the third conventional construction example, an
uncontrollable clearance is formed between the two half pieces of
the dielectric strip during production if the two half pieces are
arranged side by side and an operating band of the mode suppressor
is shifted due to the presence of an area having a different
dielectric constant between the two half pieces even if the two
pieces are secured by the adhesive. The mode suppressor cannot
effectively function in the case of deviating from a frequency band
suppressable by the mode suppressor. Further, if, for example, the
circulator and the metal plate are displaced from each other due to
the displacement of the two half pieces of the dielectric strip,
the operating band of the circulator is changed, with the result
that the circulator may not properly function.
[0020] Further, in the NRD guide disclosed in Japanese Unexamined
Patent Publication No. 63-185101 in which the metal plate of a
specified shape and the dielectric strip made of, e.g., polystyrene
are integrally formed, it is difficult to control a position where
the metal plate is formed. If the position of the metal plate is
displaced, the function as a mode suppressor is impaired. Further,
if the width of the dielectric strip is narrow, it becomes
difficult to handle the metal plate, making it impossible to
precisely provide the metal plate in a specified position.
[0021] If the dielectric strip is made of Teflon, the position of
the dielectric strip may be undesirably displaced while being
handled since it is difficult to secure Teflon by an adhesive.
[0022] It has been also difficult to suppress a transmission loss
of a high-frequency signal to or below a specified value in any of
the NRD guides according the third conventional construction.
[0023] Next, a fourth construction example of the conventional NRD
guide is described. Similar to the third conventional construction
example, the NRD guide of the fourth construction example is
constructed such that a mode suppressor is integrally provided by
arranging a conductive layer inside the dielectric strip. Similar
to the one shown in FIG. 34, a conventional NRD guide for
transmitting high-frequency signals of a microwave and a millimeter
wave is constructed by providing a dielectric strip having
quadrilateral, e.g., rectangular cross section between a pair of
parallel plate conductors opposed to each other at a specified
spacing. By setting the spacing between the parallel plate
conductors at .lambda./2 or shorter when a wavelength of a
high-frequency signal is .lambda., the high-frequency signal can be
transmitted by the dielectric strip while eliminating entrance of
noise into the dielectric strip from the outside and radiation of
the high-frequency signal to the outside. As described above, the
wavelength .lambda. is a wavelength in the air (free space) at an
operating frequency.
[0024] The operation mode of the high-frequency signal
(electromagnetic wave) transmitting in the dielectric strip of such
an NRD guide is the LSM mode as described above. However, the
unnecessary LSE mode occurs at a circulator, a high-frequency
oscillating portion and the like which are assembled into the NRD
guide. A mode suppressor is provided at an end of the dielectric
strip in order to effectively suppress this LSE mode by
attenuation.
[0025] This conventional mode suppressor is shown in FIGS. 36 and
37. In FIGS. 36 and 37, identified by 705, 706 are parallel plate
conductors which are parallelly arranged at a spacing of half the
wavelength of a high-frequency signal, by 707 a dielectric strip
made of Teflon, polystyrene or like material, and by 708 a mode
suppressor provided at the leading end of the dielectric strip 707.
The mode suppressor 708 is formed by arranging a strip conductor
709 in the leading end of the dielectric strip 707 for blocking a
millimeter wave signal of the LSE mode whose electric field is
parallel to a transmission direction of the high-frequency
direction in the dielectric strip 707 and also to a plane
perpendicular to the principle planes of the parallel plate
conductors 705, 706.
[0026] Specifically, the mode suppressor 708 is formed by arranging
a conductive layer of Cu, Au, Ag or like material along a direction
perpendicular to the principle planes of the parallel plate
conductors 705, 706 and along a signal transmission direction at a
widthwise center position of the dielectric strip 707. In order to
eliminate a TEM mode into which the LSE mode is converted at this
conductive layer, wide portions (width W1) and narrow portions
(width W2) are alternately formed at intervals of L which is 1/4 of
the wavelength .lambda. of the electromagnetic wave of the TEM
mode, i.e., a so-called .lambda./4 choke pattern is formed (see
Japanese-Unexamined Patent Publication No. 63-185101).
[0027] There has been also proposed another conventional NRD guide
in which conductive pins whose dimension along the signal
transmission direction is 1/4 or shorter than the wavelength
between the dielectric strips of a transmission mode are arranged
at an interval which is 1/4 or shorter than the wavelength between
the dielectric strips of the transmission mode in such a manner as
to extend in a direction perpendicular to the upper and lower
conductive plates in the dielectric strip at a widthwise center
position of the dielectric strip, thereby enabling low-cost
production of precise NRD guides having a uniformed variation of
production characteristics (Japanese Unexamined Patent Publication
No. 9-219608).
[0028] However, in the fourth conventional construction example
having the mode suppressor disclosed in Japanese Unexamined Patent
publication No. 63-185101, the TEM mode can be effectively
suppressed, but there are cases where the entire more suppressor
experiences resonance with unnecessary modes other than the TEM
mode, undesirably resulting in insufficient attenuation of the LSE
mode and like modes.
[0029] Further, since the mode suppressor disclosed in Japanese
Unexamined Patent Publication No. 9-219608 is considerably thick:
about 1/3 of the width of a block used as the dielectric strip,
reflection of the LSM mode which is a transmission mode occurs,
with result that a transmission loss is likely to increase.
[0030] It has been also difficult to suppress a transmission loss
of a high-frequency signal to or below a specified value in any of
the NRD guides according the fourth conventional construction.
[0031] Next, a fifth construction example of the conventional NRD
guide is described. A circulator is incorporated into the NRD
guides according to the fifth conventional construction example. A
basic construction of the NRD guide incorporating the circulator
is, similar to the one shown in FIG. 34, such that a dielectric
strip having quadrilateral, e.g., rectangular cross section is
arranged between a pair of parallel plate conductors opposed to
each other at a specified spacing. By setting the spacing between
the parallel plate conductors at .lambda./2 or shorter when a
wavelength of a high-frequency signal is .lambda., the
high-frequency signal can be transmitted by the dielectric strip
while eliminating entrance of noise into the dielectric strip from
the outside and radiation of the high-frequency signal to the
outside. As described above, the wavelength .lambda. is a
wavelength in the air (free space) at an operating frequency.
[0032] The conventional circulator incorporated into such an NRD
guide is shown in FIG. 38. In FIG. 38, identified by 710, 711, 712
are dielectric strips made of Teflon, polystyrene or like material,
by 713, 714, 715 mode suppressors provided at the leading ends of
the respective dielectric strips 710, 711, 712 and formed by
providing strip conductors 716, 717, 718 made of a copper foil in
the dielectric strips 710, 711, 712 for blocking electromagnetic
waves of the LSE mode, and by 719, 720 two ferrite disks which act
as a circulator and are connected with the leading ends of the
respective mode suppressors 713, 714, 715 and from which the
dielectric strips 710, 711, 712 radially extend at an interval of
120.degree.. The strip conductors 716, 717, 718 are formed in a
.lambda./4 choke pattern in order to eliminate the TEM (transverse
electromagnetic) mode (see "Millimeter Wave Integrated Circuit
Using a NRD guide (By Yoneyama)", pp.87-94 of "Electronic
Information Communication Meeting Conference Papers C-I Vol.J73-C-1
No. 3, Mar. 1990).
[0033] In such a construction, the electromagnetic wave having
transmitted in the dielectric strip 710 has its wavefront rotated
counterclockwise by the ferrite disks 719, 720 and is transmitted
to the dielectric strip 711, but is not transmitted to the
dielectric strip 712. Likewise, the electromagnetic wave having
transmitted in the dielectric strip 711 is transmitted to the
dielectric strip 712. In this way, transmission paths of the
electromagnetic waves are changed.
[0034] In an NRD guide provided with the circulator and the
dielectric strips, stepped portions 732, 733, 734 having a height
equal to the thickness of the ferrite disks 730, 731 are formed in
the upper and lower surfaces at the leading ends of mode
suppressors 724, 725, 726, and the two ferrite disks 730, 731 are
supported by the mode suppressors 724, 725, 726 by engaging the
ferrite disks 730, 731 with the upper and lower stepped portions
732, 733, 734 as shown in FIG. 39, thereby ensuring the
concentricity of the ferrite disks 730, 731 with a better
repeatability and a higher precision (see Japanese Unexamined
Patent Publication No. 9-186507). In FIG. 39, identified by 721,
722, 723 are dielectric strips, and by 727, 728, 729 strip
conductors made of a copper foil or the like for constructing the
mode suppressors 724, 725, 726.
[0035] In the fifth conventional construction example, the
circulator for the NRD guide is mainly constructed by the two
ferrite disks 719, 720 concentrically arranged while being
vertically spaced from each other at a specified distance. In the
construction shown in FIG. 38, a cylindrical dielectric spacer 760
for arranging the two ferrite disks at a specified spacing is
necessary. In the conventional circulator using the dielectric
spacer 760, a pass frequency band is narrowed and frequency varies
as a relative dielectric constant changes due to the thickness of
the cylindrical dielectric spacer 760. As a result, a center
frequency of the pass frequency band has been undesirably
shifted.
[0036] On the other hand, in the construction shown in FIG. 39,
assembling repeatability of the circulator is improved and the
upper and lower ferrite disks 730, 731 are free from eccentricity
since the stepped portions 732, 733, 734 are formed at the leading
ends of the mode suppressors 724, 725, 726. Thus, band
characteristics of positive pass frequencies between ports of the
respective dielectric strips are equal to each other and take a
trapezoidal form symmetrical with respect to a center frequency of
the pass band. As a result, flat pass band characteristic and
isolation characteristics symmetrical with respect to the center
frequency can be obtained.
[0037] However, besides the flat pass band characteristic,
essential characteristics required for the circulator include the
one for reducing reflection of the high-frequency signal at the
circulator portion by reducing the transmission loss (insertion
loss). This characteristic is not referred to by the prior art.
[0038] As a construction for improving a transmission loss, there
has been proposed the one in which the leading end of a mode
suppressor of a dielectric strip is cut off to form a step and a
step-shaped impedance converter is provided, thereby improving an
insertion loss and an isolation (see Singakugiho MW83-135, pp 63-66
(by Yoneyama, Sugatani, Nishida), 1984). However, in this proposed
construction, a band width of an insertion loss of 1 dB in a band
of 50 GHz is about 1.5 GHz, isolation is a minimum of 24 dB and a
maximum of 30 dB in this band. The width of the band where the
insertion loss and the isolation are improved is narrow and,
therefore, effects of the improvement are insufficient. Further, it
is difficult to finely process the dielectric strip to narrow its
width stepwise, thereby standing as a hindrance to
mass-productivity.
[0039] It has been also difficult to suppress a transmission loss
of a high-frequency signal to or below a specified value in any of
the NRD guides according the fifth conventional construction.
[0040] Next, a sixth construction example of the conventional NRD
guide is described. In the NRD guide according to the sixth
conventional construction example, a waveguide is connected with a
dielectric strip. As described above, the use of the NRD guide
constructed by tightly holding the dielectric strip by the pair of
parallel plate conductors as one type of the transmission strip of
the high-frequency signal is known. In the case that this NRD guide
is assembled on a circuit board, it is essential in designing a
circuit to connect it with an other transmission strip for a
high-frequency signal, an antenna or the like. In such a case, it
is important to connect them without deteriorating transmission
characteristics.
[0041] As a construction for connecting the NRD guide with an other
high-frequency transmission strip, a construction for connecting it
with a micro-strip has been proposed. A general construction
thereof is shown in FIG. 40. In the construction shown in FIG. 40,
a dielectric strip 743 is arranged between a pair of parallel plate
conductors in an NRD guide. A slot 744 is formed in one parallel
plate conductor 741, and the NRD guide and a micro-strip are
electromagnetically connected via the slot 744 by placing a
dielectric substrate 746 having a center conductor 745 formed on
its outer surface on the parallel plate conductor 741 such that the
slot 744 and a rear end of the center-conductor 745 have a
specified positional relationship.
[0042] Although unillustrated, there is also known, as a
construction for connecting a dielectric strip of an NRD guide and
a waveguide, a construction in which an input port or output port
of the dielectric strip is tapered and one end of the waveguide in
the form of a rectangular horn is arranged in proximity to the
tapered portion.
[0043] However, in the type of the sixth conventional construction
example in which the end of the dielectric strip is tapered as
described above when the dielectric strip of the NRD guide and the
waveguide are connected, the length of the tapered portion needs to
be longer than twice the wavelength of a high-frequency signal.
This is disadvantageous in miniaturizing the millimeter wave
integrated circuit.
[0044] The construction shown in FIG. 40 is advantageous in terms
of miniaturization. However, in the connecting construction using
the micro-strip, a transmission loss itself increases when the
frequency of the high-frequency signal lies in a millimeter band at
or above 30 GHz. This connecting construction is not suitable for
the circuit board whose signal frequency is 30 GHz or longer.
[0045] It has been also difficult to suppress a transmission loss
of a high-frequency signal to or below a specified value in any of
the NRD guides according the sixth conventional construction.
SUMMARY OF THE INVENTION
[0046] It is an object of the present invention to provide an
excellent NRD guide and a millimeter wave transmitting/receiving
apparatus which are free from the problems residing in the prior
art.
[0047] According to an aspect of the invention, a NRD guide
comprises a pair of parallel plate conductors opposed to each other
at a spacing equal to or shorter than half the wavelength of a
high-frequency signal to be transmitted and having opposing inner
surfaces whose arithmetic average roughness Ra satisfies 0.1
.mu.m.ltoreq.Ra.ltoreq.50 .mu.m, and a dielectric strip arranged
between the pair of parallel plate conductors while being held in
contact with the respective inner surfaces of the parallel plate
conductors.
[0048] With this construction, since the parallel plate conductors
are formed such that the arithmetic average roughness Ra of their
inner surfaces satisfies 0.1 .mu.m.ltoreq.Ra.ltoreq.50 .mu.m, the
inner surfaces have a suitable unevenness, and the dielectric strip
is strongly secured to the inner surfaces by the anchor effect to
exhibit an excellent durability. Further, current paths on the
inner surfaces can be shortened to reduce a surface resistance,
with the result that a transmission loss of the high-frequency
signal can be effectively suppressed.
[0049] According to another aspect of the invention, a millimeter
wave transmitting/receiving apparatus comprises: a pair of parallel
plate conductors opposed to each other at a spacing equal to or
shorter than half the wavelength of a high-frequency signal to be
transmitted; a circulator made of two ferromagnetic plates provided
between the pair of parallel plate conductors and opposed to each
other in the same direction as the pair of parallel plate
conductors are spaced apart; a first dielectric strip arranged
between the pair of parallel plate conductors; a millimeter wave
signal oscillator provided at one end of the first dielectric strip
for outputting a millimeter wave signal to be transmitted; a second
dielectric strip connected with the one end of the first dielectric
strip and radially arranged with respect to the circulator between
the pair of parallel plate conductors; a third dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors and having a transmitting/receiving
antenna at its leading end; a fourth dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; first, second, third and fourth mode
suppressors arranged between the one end of the first dielectric
strip and the millimeter wave signal oscillator and between the
second, third and fourth dielectric strips and the circulator, and
formed by arranging a plurality of conductive layers at specified
intervals in a plane parallel to a transmission direction of a
high-frequency signal inside the ends of the respective dielectric
strips; and a mixer for mixing part of the millimeter wave signal
outputted from the millimeter wave signal oscillator and a radio
wave received by the transmitting/receiving antenna to generate an
intermediate-frequency signal by coupling an intermediate position
of the first dielectric strip and that of the fourth dielectric
strip to each other.
[0050] With this construction, the electromagnetic waves of the LSE
mode or the like which is an unnecessary mode can be effectively
attenuated, and the transmission loss of the electromagnetic waves
of the LSM mode or the like which is a transmission mode is
reduced. Further, since part of the transmitted wave is introduced
to the mixer via the circulator to a reduced degree, an excellent
transmission characteristic of the millimeter wave signal is
obtained and noise of the received wave is reduced to increase a
detection distance in the case that this millimeter wave
transmitting/receiving apparatus is applied to a millimeter wave
radar or the like.
[0051] According to still another aspect of the invention, a
millimeter wave transmitting/receiving apparatus comprises: a pair
of parallel plate conductors opposed to each other at a spacing
equal to or shorter than half the wavelength of a high-frequency
signal to be transmitted; a circulator made of two ferromagnetic
plates provided between the pair of parallel plate conductors and
opposed to each other in the same direction as the pair of parallel
plate conductors are spaced apart; a first dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors; a millimeter wave signal oscillator
provided at one end of the first dielectric strip for outputting a
millimeter wave signal to be transmitted; a second dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors and having a transmitting antenna at
its leading end; a third dielectric strip radially arranged with
respect to the circulator between the pair of parallel plate
conductors; first, second, third and fourth mode suppressors
arranged between one end of the first dielectric strip and the
millimeter wave signal oscillator and between the first, second and
third dielectric strips and the circulator, and formed by arranging
a plurality of conductive layers at specified intervals in a plane
parallel to a transmission direction of a high-frequency signal
inside the ends of the respective dielectric strips; a fourth
dielectric strip having one end connected with the first or second
dielectric strip between the pair of parallel plate conductors for
transmitting part of the millimeter wave signal outputted from the
millimeter wave signal oscillator; a fifth dielectric strip
arranged between the pair of parallel plate conductors and having a
receiving antenna at its leading end; and a mixer for mixing part
of the millimeter wave signal outputted from the millimeter wave
signal oscillator and a radio wave received by the receiving
antenna to generate an intermediate-frequency signal by coupling an
intermediate position of the fourth dielectric strip and that of
the fifth dielectric strip to each other.
[0052] With this construction, the electromagnetic waves of the LSE
mode or the like which is an unnecessary mode can be effectively
attenuated, and the transmission loss of the electromagnetic waves
of the LSM mode or the like is reduced. Further, the millimeter
wave signal received by the transmitting antenna is not introduced
to the millimeter wave signal oscillator. Accordingly, an excellent
transmission characteristic of the millimeter wave signal is
obtained and noise caused by oscillation is reduced to increase a
detection distance in the case that this millimeter wave
transmitting/receiving apparatus is applied to a millimeter wave
radar module.
[0053] According to yet still another aspect of the invention, a
millimeter wave transmitting/receiving apparatus comprises: a pair
of parallel plate conductors opposed to each other at a spacing
equal to or shorter than half the wavelength of a millimeter wave
signal to be transmitted; a circulator made of two ferromagnetic
plates provided between the pair of parallel plate conductors and
opposed to each other in the same direction as the pair of parallel
plate conductors being spaced apart; :a first dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors; a millimeter wave signal oscillator
provided at one end of the second dielectric strip for outputting
the millimeter wave signal to be transmitted; a second dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors, and having a
transmitting/receiving antenna at it leading end; a third
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a fourth dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors, and having one end connected
with the first dielectric strip; first, second and third mode
suppressors arranged between the first, second and third dielectric
strips and the circulator for suppressing electromagnetic waves of
unnecessary modes; first, second and third impedance matching
members arranged at the end faces of the first, second and third
mode suppressors toward the circulator and having a relative
dielectric constant different from that of the first, second and
third dielectric strips; and a mixer for mixing part of the
millimeter wave signal outputted from the millimeter wave signal
oscillator and having transmitted in the fourth dielectric strip
and a radio wave received by the transmitting/receiving antenna to
generate an intermediate-frequency signal and transmitted in the
third dielectric strip by coupling an intermediate position of the
third dielectric strip and that of the fourth dielectric strip to
each other.
[0054] With this construction, the transmission loss and isolation
characteristic of the millimeter wave signal in a high-frequency
band having a wide range are further improved, with the result that
a detection distance can be increased in the case that this
millimeter wave transmitting/receiving apparatus is applied to a
millimeter wave radar or the like.
[0055] According to further aspect of the invention, a millimeter
wave transmitting/receiving apparatus comprises: a pair of parallel
plate conductors opposed to each other at a spacing equal to or
shorter than half the wavelength of a millimeter wave signal to be
transmitted; a circulator made of two ferromagnetic plates provided
between the pair of parallel plate conductors and opposed to each
other in the same direction as the pair of parallel plate
conductors are spaced apart; a first dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; a millimeter wave signal oscillator
provided at one end of the first dielectric strip for outputting
the millimeter wave signal to be transmitted; a second dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors and having a transmitting antenna
at its leading end; a third dielectric strip radially arranged with
respect to the circulator between the pair of parallel plate
conductors; first, second and third mode suppressors arranged
between the first, second, and third dielectric strips and the
circulator for suppressing electromagnetic waves of unnecessary
modes; first, second and third impedance matching members arranged
at the end faces of the first, second and third mode suppressors
toward the circulator and having a relative dielectric constant
different from that of the second, third and fourth dielectric
strips; a fourth dielectric strip having one end connected with the
first dielectric strip between the pair of parallel plate
conductors for transmitting part of the millimeter wave signal
outputted from the millimeter wave signal oscillator; a fifth
dielectric strip arranged between the pair of parallel plate
conductors and having a receiving antenna at its leading end; and a
mixer for mixing part of the millimeter wave signal outputted from
the millimeter wave signal oscillator and a radio wave received by
the receiving antenna to generate an intermediate-frequency signal
by coupling an intermediate position of the fourth dielectric strip
and that of the fifth dielectric strip to each other.
[0056] With this construction, the transmission loss and isolation
characteristic of the millimeter wave signal in a high-frequency
band having a wide range are further improved. Further, the
millimeter wave signal to be transmitted is not introduced to the
mixer via the circulator. Accordingly, noise of the received signal
is reduced to increase a detection distance, and an excellent
transmission characteristic of the millimeter wave -signal further
increases the detection distance of a millimeter wave radar in the
case that this millimeter wave transmitting/receiving apparatus is
applied to a millimeter wave radar module.
[0057] According to still further aspect of the invention, a
millimeter wave transmitting/receiving apparatus comprises: a pair
of parallel plate conductors opposed to each other at a spacing
equal to or shorter than half the wavelength of a millimeter wave
signal to be transmitted; a circulator made of two ferromagnetic
plates provided between the pair of parallel plate conductors and
opposed to each other in the same direction as the pair of parallel
plate conductors being spaced apart; a first dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors; a millimeter wave signal oscillator
provided at one end of the first dielectric strip for outputting
the millimeter wave signal to be transmitted; a second dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors; a third dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors; a fourth dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; a metallic waveguide having an open
termination at one end connected with an opening formed in at least
one of the pair of parallel plate conductors in a position
corresponding to where the electric field of a standing wave of LSM
mode transmitting in the third dielectric strip is at maximum while
having an open termination at the other end provided with a
transmitting/receiving antenna; a mixer for mixing part of the
millimeter wave signal from the millimeter wave signal oscillator
having transmitted, in the fourth dielectric strip and a radio wave
having transmitted in the third dielectric strip and received by
the transmitting/receiving antenna to generate an
intermediate-frequency signal by coupling an intermediate position
of the third dielectric strip and that of the fourth dielectric
strip to each other.
[0058] With this construction, an excellent transmission
characteristic of the millimeter wave signal can be obtained, which
in turn increases a detection distance of a millimeter wave
radar.
[0059] According to yet further aspect of the invention, a
millimeter wave transmitting/receiving apparatus, comprising: a
pair of parallel plate conductors opposed to each other at a
spacing equal to or shorter than half the wavelength of a
millimeter wave signal to be transmitted; a circulator made of two
ferromagnetic plates provided between the pair of parallel plate
conductors and opposed to each other in the same direction as the
pair of parallel plate conductors being spaced apart; a first
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a millimeter wave
signal oscillator provided at one end of the second dielectric
strip for outputting the millimeter wave signal to be transmitted;
a second dielectric strip radially arranged with respect to the
circulator between the pair of parallel plate conductors; a third
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a fourth dielectric
strip having one end connected with the first dielectric strip
between the pair of parallel plate conductors for transmitting part
of the millimeter wave signal outputted from the millimeter wave
signal oscillator; a fifth dielectric strip arranged between the
pair of parallel plate conductors; a first metallic waveguide
having an open termination at one end connected with an opening
formed in at least one of the pair of parallel plate conductors in
a position corresponding to where the electric field of a standing
wave of LSM mode transmitting in the second dielectric strip is at
maximum while having an open termination at the other end provided
with a transmitting antenna; a second metallic waveguide having an
open termination at one end connected with an opening formed in at
least one of the pair of parallel plate conductors in a position
corresponding to where the electric field of a standing wave of LSM
mode transmitting in the fifth dielectric strip is at maximum while
having an open termination at the other end provided with a
receiving antenna; and a mixer for mixing part of the millimeter
wave signal outputted from the millimeter wave signal oscillator
and a radio wave received by the receiving antenna to generate an
intermediate-frequency signal by coupling an intermediate position
of the fourth dielectric strip and that of the fifth dielectric
strip to each other.
[0060] With this construction, the millimeter wave signal to be
transmitted is not introduced to the mixer via the circulator. As a
result, noise of the received signal is reduced to increase a
detection distance, and an excellent transmission characteristic of
the millimeter wave signal further increases the detection distance
of a millimeter wave.
[0061] These and other objects, features and advantages of the
present invention will become more apparent upon a reading of the
following detailed description and-accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] FIG. 1 is a perspective view showing an inside of a NRD
guide according to a first embodiment of the invention;
[0063] FIG. 2 is a graph showing an attenuation of a high-frequency
signal in relation to a spacing between strip sections of the NRD
guide shown in FIG. 1;
[0064] FIG. 3 is a schematic section showing a NRD guide according
to a second embodiment of the invention;
[0065] FIG. 4 is a schematic section showing another construction
of the NRD guide according to the second embodiment of the
invention;
[0066] FIG. 5 is a perspective view showing an inside of a NRD
guide according to a third embodiment of the invention;
[0067] FIG. 6 is a diagram showing an example of a pattern of a
conductive layer in a mode suppressor used in the NRD guide shown
in FIG. 5;
[0068] FIG. 7 is a perspective view partly cut away and partly
in-section showing an inside of a NRD guide according to a fourth
embodiment of the invention;
[0069] FIG. 8 is a diagram showing an example of a pattern of
conductive layers in a mode suppressor used in the NRD guide shown
in FIG. 7;
[0070] FIG. 9A is a plan view of a millimeter wave radar module in
which the NRD guide-shown in FIG. 7 is used;
[0071] FIG. 9B is a perspective view of a nonreflective termination
in the millimeter wave radar module shown in FIG. 9A;
[0072] FIG. 10A is a plan view of a millimeter wave radar module in
which the NRD guide shown in FIG. 7 is used;
[0073] FIG. 10B is a perspective view of a nonreflective
termination in the millimeter wave radar module shown in FIG.
10A;
[0074] FIG. 11 is a perspective view showing a millimeter wave
signal oscillator of voltage control type used in the-millimeter
wave radar modules shown in FIGS. 9A or 10;
[0075] FIG. 12 is a perspective view of a circuit board on which a
varactor diode is provided for the millimeter wave signal
oscillator shown in FIG. 11;
[0076] FIG. 13 is a graph showing a measurement result of a
transmission characteristic of an LSE mode for a mode suppressor
used in the NRD guide shown in FIG. 7;
[0077] FIG. 14 a graph showing a measurement result of a
transmission characteristic of the LSE mode for a conventional mode
suppressor for comparison;
[0078] FIG. 15 is a perspective view showing an internal
construction of an essential portion of a NRD guide according to a
fifth embodiment of the invention;
[0079] FIG. 16 is a side view showing an essential portion of the
NRD guide shown in FIG. 15;
[0080] FIG. 17A is a plan view of a millimeter wave radar module in
which the NRD guide shown in FIGS. 15 and 16 is used;
[0081] FIG. 17B is a perspective view of a nonreflective
termination in the millimeter wave radar module shown in FIG.
17A;
[0082] FIG. 18A is a plan view of a millimeter wave radar module in
which the NRD guide shown in FIGS. 15 and 16 is used;
[0083] FIG. 18B is a perspective view of a nonreflective
termination in the millimeter wave radar module shown in FIG.
18A;
[0084] FIG. 19 is a perspective view showing a millimeter wave
signal oscillator of voltage control type used in the millimeter
wave radar modules shown in FIGS. 17A or 18;
[0085] FIG. 20 is a perspective view of a circuit board on which a
varactor diode is provided for the millimeter wave signal
oscillator shown in FIG. 19;
[0086] FIG. 21 is a graph showing measurement results of a
transmission characteristic .vertline.S21.vertline. and an
isolation .vertline.S31.vertline. of a high-frequency signal for
the NRD guide shown in FIGS. 15 and 16;
[0087] FIG. 22 is a graph showing measurement results of the
transmission characteristic .vertline.S21.vertline. and the
isolation .vertline.S31.vertline. of the high-frequency signal for
a conventional NRD guide shown in FIG. 39;
[0088] FIG. 23 is a perspective view showing a NRD guide according
to a sixth embodiment of the invention in which a metallic
waveguide is connected with a dielectric strip in a direction
perpendicular to principle planes of parallel plate conductors;
[0089] FIG. 24 is a plan view showing an electric field
distribution of the dielectric strip in the NRD guide;
[0090] FIG. 25 is a perspective view showing another construction
of the NRD guide according to the sixth embodiment of the invention
in which the metallic waveguide is connected with the dielectric
strip in a direction parallel to the principle planes of the
parallel plate conductors;
[0091] FIG. 26 is a partial perspective view showing a construction
of the NRD guide shown in FIG. 23 in which an open termination of
the dielectric strip is widened;
[0092] FIG. 27 is a perspective view showing still another
construction of the NRD guide according to the sixth embodiment of
the invention in which the metallic waveguide having an antenna
member provided at its other end is connected with the dielectric
strip in a direction perpendicular to the principle planes of the
parallel plate conductors;
[0093] FIG. 28A is a plan view of a millimeter wave radar module in
which the NRD guide shown in FIGS. 23, 25 or 26 is used;
[0094] FIG. 28B is a perspective view of a nonreflective
termination in the millimeter wave radar module shown in FIG.
28A;
[0095] FIG. 29A is a plan view of a millimeter wave radar module in
which the NRD guide shown in FIGS. 23, 25 or 26 is used;
[0096] FIG. 29B is a perspective view of a nonreflective
termination in the millimeter wave radar module shown in FIG.
29A;
[0097] FIG. 30 is a perspective view showing a millimeter wave
signal oscillator used in the millimeter wave radar module shown in
FIGS. 28A or 29;
[0098] FIG. 31 is a perspective view of a circuit board on which a
variable-capacitance diode is provided for the millimeter wave
signal oscillator shown in FIG. 30;
[0099] FIG. 32 is a graph showing a high-frequency signal
transmission characteristic of the NRD guide shown in FIG. 23;
[0100] FIG. 33 is a graph showing a high-frequency signal
transmission characteristic of the NRD guide shown in FIG. 26;
[0101] FIG. 34 is a perspective view showing an inside of a
conventional NRD guide;
[0102] FIG. 35 is a perspective view showing an inside of another
conventional NRD guide;
[0103] FIG. 36 is a perspective view showing an inside of still
another conventional NRD guide;
[0104] FIG. 37 is a side view showing a pattern of a conductive
layer for a mode suppressor in the conventional NRD guide shown in
FIG. 36;
[0105] FIG. 38 is a perspective view showing an essential portion
of yet still another conventional NRD guide;
[0106] FIG. 39 is a perspective view showing an essential portion
of a further conventional NRD guide; and
[0107] FIG. 40 is a perspective view showing a still further
conventional NRD guide.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0108] FIG. 1 is a perspective view showing a NRD guide
(hereinafter, "NRD guide") according to a first embodiment of the
invention. An NRD guide S1 according to the first embodiment is
mainly designed to solve the problems in the prior art. In FIG. 1,
identified by 101, 102 are a pair of parallel plate conductors
vertically opposed to each other at a spacing which is equal to or
shorter than half the wavelength of a high-frequency signal to be
transmitted. Identified by 103 is a dielectric strip secured
between the pair of parallel plate conductors 101, 102 by an
adhesive and is comprised of three strip sections 103a, 103b, 103c.
These three strip sections 103a, 103b, 103c are arranged such that
ends faces thereof substantially perpendicular to a high-frequency
signal transmission direction are opposed to each other at a
spacing L which is equal to or shorter than 1/8 of the wavelength
of the high-frequency signal. The end faces of the strip sections
103a, 103b, 103c may be substantially perpendicular to the
high-frequency signal, and may not necessarily be perfectly
perpendicular thereto. Further, these end faces may not be flat,
but may be curved to a certain degree.
[0109] The respective parallel plate conductors 101, 102 are formed
of conductive plates made of, e.g., Cu, Al, Fe, SUS (Stainless
Steel), Ag, Au, Pt since they need to have a high electric
conductivity and an excellent processability. Alternatively, they
may be formed of insulating plates made of ceramics, resin or like
material having a conductive layer made of the above metallic
materials formed on its outer surface. Further, the surfaces (inner
surfaces) of the parallel plate conductors 101, 102 facing the
dielectric strip 103 are ground so that an arithmetic average
roughness Ra thereof satisfies 0.1 .mu.m.ltoreq.Ra.ltoreq.50
.mu.m.
[0110] This arithmetic average roughness Ra is defined by Japanese
Industrial Standards (JIS) B0601-1994. Specifically, the arithmetic
average roughness Ra is a value obtained by following equation (1)
when a surface is extracted by a reference length L from a
roughness curve in its average line, and the roughness curve is
expressed by y=f(x) by taking-an X-axis in a direction of an
average line of the extracted section and a Y-axis in a direction
of longitudinal magnification, and is expressed in micrometer
(.mu.m). Here, the roughness curve refers to a curve obtained by
removing surface swelling components longer than a predetermined
wavelength from a section curve which is an outline appearing at a
cut end when a surface of an object (object surface) is cut by a
plane perpendicular to the object surface by a phase-compensating
high-pass filter.
[0111] [Equation 1]
Ra=(1/L).intg..sub.0.sup.1.vertline.f(x).vertline.dx (1)
[0112] The arithmetic average roughness Ra is set in the above
numerical range as a result of various trials and errors.
Specifically, a lower limit of the range of the arithmetic average
roughness Ra is set at 0.1 .mu.m because it was found out to be
difficult to strongly hold the dielectric strip 103 secured to the
parallel plate conductors 101, 102 by the adhesive or the like over
a long time, making the dielectric strip 103 easy to peel off from
the parallel plate conductors 101, 102 as time passes (i.e., poor
durability) if Ra is smaller than 0.1 .mu.m. The lower limit of the
arithmetic average roughness Ra needs to be 0.1 .mu.m since the
adhesive is strongly secured to the inner surfaces by the anchor
effect if the inner surfaces have a suitable unevenness.
[0113] Further, an upper limit of the arithmetic average roughness
Ra is set at 50 .mu.m for the following reason. Currents created in
the parallel plate conductors 101, 102 by the high-frequency signal
are concentrated on the inner surface of the parallel plate
conductors 101, 102 due to the skin effect. If the arithmetic
average roughness Ra is larger than 50 .mu.m, it was found out that
current paths on the inner surface became longer to increase a
surface resistance, with the result that a transmission loss of the
high-frequency signal is increased to increase a transmission loss.
Thus, the upper limit of the arithmetic average roughness Ra needs
to be 50 .mu.m in order to effectively suppress the transmission
loss. The arithmetic average roughness Ra satisfies preferably 0.3
.mu.m.ltoreq.Ra.ltoreq.25 .mu.m, and more preferably 0.4
.mu.m.ltoreq.Ra.ltoreq.10 .mu.m.
[0114] The dielectric strip 103 is made of ceramics containing a
multiple oxide of Ag, Al, Si as a main component. This ceramics
preferably has a relative dielectric constant of 4.5 to 8. The
range of the relative dielectric constant is set as above for the
following reason. In the case of the relative dielectric constant
below 4.5, electromagnetic waves of the LSM mode have a larger
tendency to be converted into those of the LSE mode as described
above. Further, if the relative dielectric constant exceeds 8, the
width of the dielectric strip 103 needs to be very narrow when
being used at a frequency of 50 GHz or higher, which makes
processing difficult to thereby degrade shape precision and
presents a problem in strength.
[0115] The spacing L between the strip sections 103a, 103b, 103c of
the dielectric strip 103 is set equal to or shorter than .lambda./8
(.lambda.: wavelength of the high-frequency signal). This is
because the transmission loss of the high-frequency signal
increases if the spacing L is longer than .lambda./8. The spacing L
is desirably set equal to or shorter than .lambda./16 in the case
the number of the strip sections 103a, 103b, 103c increases or a
lower transmission loss is required.
[0116] Ceramics containing a multiple oxide of Mg, Al, Si as a main
component and having a Q-value of 1000 or larger at an operating
frequency of 50 to 90 GHz is preferably used as a material of the
dielectric strip 103 of the NRD guide S1 according to the first
embodiment. This is to realize a sufficiently low transmission loss
for the dielectric strip which has been used at a frequency range
of 50 to 90 GHz included in the microwave band and millimeter wave
band in recent years.
[0117] The material of the dielectric strip 103 for-realizing such
a characteristic contains a multiple oxide of Mg, Al, Si as a main
component, which multiple oxide satisfies: x=10 to 40 mole percent,
y=10 to 40 mole percent, z=20 to 80 mole percent when a mole ratio
composition formula thereof is expressed by
xMgO.yAl.sub.2O.sub.3.zSiO.sub.2.
[0118] A composition of the main component of the ceramics
(dielectric ceramic composition) as the material of the dielectric
strip 103 according to the first embodiment is limited to the above
range for the following reason. Specifically, x representing mole
percent of the MgO is set at 10 to 40 mole percent because
satisfactory sintered matters cannot be obtained if x is below 10
mole percent and the relative dielectric constant increases if x
exceeds 40 mole percent. It is particularly desirable to set x at
15 to 35 mole percent since the Q-value is 2000 or larger at 60
GHz.
[0119] Further, y representing mole percent of the Al.sub.2O.sub.3
is set at 10 to 40 mole percent because satisfactory sintered
matters cannot be obtained if y is below 10 mole percent and the
relative dielectric constant increases if y exceeds 40 mole
percent. It is desirable to set y at 17 to 35 mole percent since
the Q-value is 2000 or larger at 60 GHz.
[0120] Furthermore, z representing mole percent of the SiO.sub.2 is
set at 20 to 80 mole percent because the relative dielectric
constant increases if z is below 20 mole percent and satisfactory
sintered matters cannot be obtained, and no satisfactory sintered
manner can be obtained and the Q-value decreases if z exceeds 80
mole percent. It is desirable to set z at 30 to 65 mole percent
since the Q-value is 2000 or larger at 60 GHz.
[0121] x, y, z representing mole percent of MgO, Al.sub.2O.sub.3,
SiO.sub.2 can be specified by an analytical method such as an EPMA
(electron probe micro analysis) method or an XRD (X-ray
diffraction) method.
[0122] The ceramics (dielectric ceramic composition) for the
dielectric strip 103 used in the first embodiment may be
precipitated into cordierite (2MgO.2Al.sub.2O.sub.3.5SiO.sub.2) as
a main crystal phase and mullite (3Al.sub.2O.sub.3.2SiO.sub.2),
spinel (MgO.Al.sub.2O.sub.3), protoenstatite (one kind of sturtite
containing magnesium metasilicate (MgO.SiO.sub.2) as a main
component), clinoenstatite (one kind of sturtite containing
magnesium silicate (MgO.SiO.sub.2) as a main component), forsterite
(2MgO.SiO.sub.2), cristobalite (one kind of silicate (SiO.sub.2)),
tridymite (one kind of silicate (SiO.sub.2), sapphirine (one kind
of silicate of Mg, Al), etc. as other crystal phases. However,
precipitation phases differ depending on the composition. It should
be noted that the dielectric ceramic composition of the first
embodiment may be a crystal phase comprised only of cordierite.
[0123] The dielectric ceramic composition for the dielectric strip
103 used in the first embodiment is produced as follows. For
example, a MgCO.sub.3 powder, an Al.sub.2O.sub.3 powder and a
SiO.sub.2 powder are used as a raw material powder, the weights
thereof are measured to have a specified weight ratio, and these
powders are dried after being mixed in a wet process. After being
provisionally burnt at 1100 to 1300.degree. C. in the air, this
mixture is crushed into powder. The obtained powder is molded by
adding a suitable amount of a resin binder, and the molded matter
is sintered at 1300 to 1450.degree. C. in the air to obtain the
dielectric ceramic composition.
[0124] The respective elements of Mg, Al, Si contained in the raw
material powder may be inorganic compounds such as oxides,
carbonates or acetates or organic compounds such as organic metals
provided that they become oxides by sintering.
[0125] The main component of the dielectric ceramic composition
used in the first-embodiment contains the multiple oxide of Mg, Al,
Si as a main component and may contain impurities of the crushed
balls and raw material powder in addition to the above elements
within such a range as not to impair the characteristic that the
Q-value is 1000 or larger at 50 to 90 GHz or may contain other
components for the purpose of controlling a sintering temperature
range and improving a mechanical characteristic. For example,
compounds of rare-earth elements, oxides of Ba, Sr, Ca, Ni, Co, In,
Ga, Ti, etc. and nonoxides such as nitrides including silicon
nitride may be contained. A single or plurality of kinds of these
compounds may be contained.
[0126] The NRD guide of the first embodiment is used in a wireless
LAN, a millimeter wave radar installed in an automotive vehicle,
etc. For example, a millimeter wave is projected to an obstacle and
other automotive vehicles present around an automotive vehicle, the
reflected wave is combined with the original millimeter wave to
obtain a beat signal (intermediate-frequency signal), and distances
to the obstacle and other automotive vehicles and their moving
speeds are measured by analyzing this beat signal.
[0127] Since the dielectric strip 103 is comprised of a plurality
of strip sections 103a, 103b, 103c in the first embodiment as
described above, it can be easily formed by linear section(s) and
curved section(s) even if it has a complicated shape formed and is
unlikely to be influenced by a stress created from a difference in
thermal expansion between the parallel plate conductors 101, 102
and the dielectric strip 103 resulting from an atmospheric
temperature change and a stress created by an external impact.
Accordingly, NRD guides which have a higher degree of freedom and
are small and inexpensive can be constructed. Further, since the
dielectric strip 103 made of ceramics having a lower relative
dielectric constant than a conventionally used aluminaceramics or
like material is used, conversion of electromagnetic waves of the
LSM mode into those of the LSE mode can be reduced and a loss of
the high-frequency signal can be suppressed.
[0128] This embodiment is not limited to the above, and may be
modified.
EXAMPLE 1
[0129] The NRD guide S1 of FIG. 1 was constructed as follows. As a
material for the dielectric strip 103, various compositions of
ceramics containing the multiple oxide of Mg, Al, Si as a main
component were prepared. Relative dielectric constants and Q-values
of these compositions at a frequency of 60 GHz are shown in
TABLE-1.
1 TABLE 1 ADDITIVE DI- COMPOSITION (weight ELECTRIC Q-VALUE MgO
Al.sub.2O.sub.3 SiO.sub.2 percent) CONSTANT (at 60 GHz) 1 5 55 40
Yb.sub.2O.sub.3 10 6.8 520 2 10 10 80 Yb.sub.2O.sub.3 10 4.8 1400 3
10 30 60 Yb.sub.2O.sub.3 15 5.8 1820 4 10 40 50 Yb.sub.2O.sub.3 0.1
5.8 1850 5 15 35 50 Yb.sub.2O.sub.3 5 5.6 2121 6 17.5 17.5 65
Yb.sub.2O.sub.3 5 4.8 2040 7 20 40 40 Yb.sub.2O.sub.3 5 5.6 1010 8
22.2 22.2 55.6 -- -- 4.7 2810 9 25 17 58 Yb.sub.2O.sub.3 10 5.1
2490 10 25 27 48 Yb.sub.2O.sub.3 10 5.6 2770 11 25.5 30 44.5
Yb.sub.2O.sub.3 10 5.8 2120 12 30 10 60 Yb.sub.2O.sub.3 5 5.2 1500
13 30 30 40 Yb.sub.2O.sub.3 5 5.6 2500 14 35 20 45 Yb.sub.2O.sub.3
10 6.0 2060 15 35 35 30 Yb.sub.2O.sub.3 0.1 5.8 2080 16 40 10 50
Yb.sub.2O.sub.3 10 5.8 1990 17 40 20 40 Yb.sub.2O.sub.3 5 5.5 1020
18 40 40 20 Yb.sub.2O.sub.3 10 6.0 1470 19 40 50 10 Yb.sub.2O.sub.3
5 7.9 520 20 58 10 32 Yb.sub.2O.sub.3 5 7.5 1250 21 22.2 22.2 55.6
Yb.sub.2O.sub.3 0.1 4.8 2910 22 22.2 22.2 55.6 Yb.sub.2O.sub.3 1
4.8 2670 23 22.2 22.2 55.6 Yb.sub.2O.sub.3 5 4.8 2750 24 22.2 22.2
55.6 Yb.sub.2O.sub.3 7 4.9 3010 25 22.2 22.2 55.6 Yb.sub.2O.sub.3
10 5.0 3010 26 22.2 22.2 55.6 Yb.sub.2O.sub.3 15 5.4 2100 27 22.2
22.2 55.6 Y.sub.2O.sub.3 10 5.0 2900 28 22.2 22.2 55.6
La.sub.2O.sub.3 10 5.0 2930 29 22.2 22.2 55.6 Nd.sub.2O.sub.3 10
5.0 2870 30 22.2 22.2 55.6 Er.sub.2O.sub.3 10 5.0 2910 31 22.2 22.2
55.6 Lu.sub.2O.sub.3 10 5.0 2990 32 22.2 22.2 55.6 Sc.sub.2O.sub.3
10 5.0 2790 33 22.2 22.2 55.6 BaO 10 4.9 2500 34 22.2 22.2 55.6 SrO
10 4.9 2890 35 22.2 22.2 55.6 CaO 10 4.9 2470 36 22.2 22.2 55.6 NiO
10 5.0 2880 37 22.2 22.2 55.6 CoO 10 5.0 2790 38 22.2 22.2 55.6
In.sub.2O.sub.3 10 5.0 2960 39 22.2 22.2 55.6 GaO.sub.2 10 5.0 2850
40 22.2 22.2 55.6 TiO.sub.2 10 5.0 2760 41 22.2 22.2 55.6
Si.sub.3O.sub.4 10 4.9 2840
[0130] As a pair of parallel plate conductors 101, 102, two copper
plates of 80 mm (longitudinal dimension)x 80 mm (lateral
dimension).times.2 mm (thickness) were arranged at a spacing of 1.8
mm, and the dielectric strip 103 made of cordierite ceramics of No.
2 of TABLE-1 was arranged between the copper plates. The dielectric
strip 103 had a rectangular cross section having a height of about
1.8 mm and a width of 0.8 mm, and the three strip sections 103a,
103b, 103c were aligned at the spacing of L. A measurement result
of a frequency characteristic of the NRD guide S1 is shown in FIG.
2. FIG. 2 is a graph showing a transmission loss
(.vertline.S21.vertline.) in relation to the spacing L at a
frequency of 77 GHz. An insertion loss by the dielectric strip 103
was 1 dB or below when the spacing L between the strip sections
103a, 103b, 103c was .lambda./8 or shorter.
[0131] Since the parallel plate conductors are formed so that the
arithmetic average roughness Ra of their inner surfaces satisfies
0.1 .mu.m.ltoreq.Ra.ltoreq.50 .mu.m as described above, the NRD
guide Si according to the first embodiment has an excellent
durability and can effectively suppress the transmission loss of
the high-frequency signal because the dielectric strip is strongly
secured to the inner surfaces of the parallel plate conductors by
the adhesive.
[0132] Preferably, the end faces of a plurality of strip sections
are opposed to each other at a spacing equal to or shorter than 1/8
of the wavelength of the high-frequency signal to be transmitted.
This can reduce conversion of electromagnetic waves of the LSM mode
into those of the LSE mode and enables an easy fabrication of the
dielectric strip having a complicated shape formed by linear and
curved portions. Further, the dielectric strip can be made unlikely
to be influenced by a stress created from a difference in thermal
expansion between the parallel plate conductors 101, 102 and the
dielectric strip 103 resulting from an atmospheric temperature
change and a stress created by an external impact. Accordingly, NRD
guides which have a higher degree of freedom and are small and
inexpensive can be constructed. Furthermore, since the dielectric
strip can be miniaturized by providing a sharply curved portion,
the entire NRD guide can be miniaturized. Even if a supporting jig
for the dielectric strip, a circuit board, and the like are made of
a resin material and are provided in vicinity of the dielectric
strip, the dielectric strip is unlikely to be influenced
thereby.
[0133] Preferably, the dielectric strip is made of ceramics
containing the multiple oxide of Mg, Al, Si as a main component and
has a Q-value of 1000 or larger at a measurement frequency of 50 to
90 GHz. This can reduce conversion of electromagnetic waves of the
LSM mode into those of the LSE mode and suppress the transmission
loss of the high-frequency signal.
[0134] FIG. 3 is a schematic section showing an NRD guide according
to a second embodiment of the invention. An. NRD guide S2 according
to the second embodiment is mainly designed to solve the problems
in the prior art. In FIG. 3, the NRD guide S2 is constructed by
arranging a dielectric strip 203 between a pair of parallel plate
conductors 201, 202 vertically opposed to each other at a spacing
which is equal to or shorter than half the wavelength of a
high-frequency signal to be transmitted. It should be noted that
the wavelength here is a wavelength in the air (free space) at an
operating frequency. In the construction of FIG. 3, the parallel
plate conductors 201, 202 and the dielectric strip 203 are joined
using a solder 204.
[0135] The respective parallel plate conductors 201, 202 are formed
of conductive plates made of, e.g., Cu, Al, Fe, SUS (Stainless
Steel), Ag, Au, Pt since they need to have a high electric
conductivity and an excellent processability. Alternatively, they
may be formed of insulating plates made of ceramics, resin or like
material having a conductive layer made of the above metallic
materials formed on its outer surface. Further, the surfaces (inner
surfaces) of the parallel plate conductors 201, 202 facing the
dielectric strip 203 are ground so that an arithmetic average
roughness Ra thereof satisfies 0.1 .mu.m.ltoreq.Ra.ltoreq.50
.mu.m.
[0136] This arithmetic average roughness. Ra is the same as the one
defined in the first embodiment, and the range thereof is set as
above for the same reason mentioned in the first embodiment. The
arithmetic average roughness Ra satisfies preferably0.3 .mu.m s
Ra.ltoreq.25 .mu.m, and more preferably 0.4
.mu.m.ltoreq.Ra.ltoreq.10 .mu.m.
[0137] The parallel plate conductors 201, 202 may be in the formed
of simple flat plates, but may also be formed with grooves
(recesses) in positions facing the dielectric strip 203 like
parallel plate conductors 207, 208 of FIG. 4 to be described
later.
[0138] On the other hand, the dielectric strip 203 may be made of a
resin dielectric material such as Teflon, polystyrene or glass
epoxy or ceramic such as cordierite, alumina, glass ceramics or
forsterite. However, in view of heat resistance required when being
secured by the solder 204, the dielectric strip 203 is desirably
made of ceramics or a glass.
[0139] In view of a dielectric characteristic, processability,
strength, miniaturization and reliability, the dielectric strip 203
is desirably made of cordierite ceramics. Further, it is desirable
to contain at least one kind of element selected from Y, La, Ce,
Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu in the cordierite ceramics.
Content of such an element can improve electric characteristics
such as a Q-value and transmit signals with a low transmission
loss.
[0140] In the case that metallic layers 205 to be described later
are formed on the outer surfaces of the dielectric strip 203 by
deposition, the dielectric strip 203 is desirably made of glass
ceramics which can be simultaneously sintered with Cu, Ag or like
metal having a low resistance. Further, the glass ceramics is
desirably such that at least one kind of SiO.sub.2 crystal phases,
spinel type crystal phases such as MgAl.sub.2O.sub.4,
ZnAl.sub.2O.sub.4, diopside type oxide crystal phases such as
Ca(Mg, Al)(Si, Al).sub.2O.sub.6, and other similar crystal phases
such as Ca.sub.2MgSi.sub.2O.sub.7 (akermanite), CaMgSiO.sub.4
(monticellite), Ca.sub.3MgSi.sub.2O.sub.8 (merwinite), ilmenite
type crystal phases such as MgTiO.sub.3, SrTiO.sub.3, BaTiO.sub.3,
CaTiO.sub.3, (Mg, Zn)TiO.sub.3, willemite type crystal phases such
as Zn.sub.2SiO.sub.4, MgSiO.sub.3, 3Al.sub.2O.sub.3.2SiO.sub.2, and
Mg.sub.2Al.sub.4Si.sub.5O.sub.18 having a small dielectric loss is
precipitated therefrom. It is desirable that the glass ceramics
contains a silica having a small dielectric loss as a main
component beside the above crystal phases.
[0141] In order to enhance the strength of the dielectric strip
203, reduce the dielectric constant and dielectric loss thereof and
adjust a thermal expansion coefficient thereof, ZnO,
Al.sub.2O.sub.3, cordierite, MgAl.sub.2O.sub.4, MgO, TiO.sub.2,
ZrO.sub.2, CaZrO.sub.3 and the like may be dispersed as a filler in
the glass ceramics in addition to the aforementioned crystal
phases.
[0142] An essential feature of the second embodiment lies in that
the parallel plate conductors 201, 202 (or 207, 208) and the
dielectric strip 203 are joined using the solder 204. This enables
precise positioning of the dielectric strip 203, thereby reducing
the transmission loss of the signal in the NRD guide due to a
displacement of the dielectric strip 203 and enabling realization
of NRD guides having high heat resistance, durability and
reliability.
[0143] The solder 204 desirably contains at least one kind of
element selected from a group of Au, Ag, Ti, Sn, Pb. Particularly,
a Au--Sn solder, a Pb--Sn solder, a Ag--Ti solder material, a Ag
solder material can be used. It is most desirable to contain a
Au--Sn solder (durability temperature of up to 320.degree. C.) as a
main component. Further, in order to prevent deterioration of the
signal transmission characteristic in the NRD guide S2, a maximum
thickness (height) of the solder 204 is desirably, 1 mm or smaller,
preferably 0.5 mm or smaller and desirably has a smooth surface
state.
[0144] In order to enhance adhesion between the dielectric strip
203 and the solder 204, it is desirable to provide the metallic
layers 205 integrally formed with the dielectric strip 203 between
the dielectric strip 203 and the solder 204. The metallic layers
205 are desirably formed of metallic foils in order to enhance
precision of the width of the dielectric strip 203, prevent the
dielectric strip 203 from warping due to sintering and enhance
smoothness of their phase boundaries with the dielectric strip 203.
Further, plating of Au/Ni or Au or like metal may be applied to the
outer surfaces of the metallic layers 205.
[0145] Although the parallel plate conductors 201, 202 are in the
formed of simple flat plates in the NRD guide S2 of FIG. 3, the
second embodiment is not limited thereto. As in, an NRD guide S2a
shown in FIG. 4, grooves (recesses) 209, 210 may be formed in
positions of the facing surfaces of the parallel plate conductors
207, 208, the solder 204 and the metallic layers 205 may be filled
in the grooves 209, 210 to a specified depth, and the dielectric
strip 203 may be secured to the outer surface of the solder
204.
[0146] In such a case, the NRD guide S2a may be formed such that
the outer surfaces of the dielectric strip 203 lie in the same
planes as the opening planes of the grooves 209, 210 in the
parallel plate conductors 207, 208 (i.e., construction shown in
FIG. 4) or such that the dielectric strip 203 is buried in the
grooves 209, 210 to a specified depth.
[0147] Although the NRD guide S2 of FIG. 3 is constructed such that
the solder 204 is provided on the both surfaces of the dielectric
strip 203 in contact with the parallel plate conductors 201, 202,
the second embodiment is not limited thereto. The solder 204 may be
provided only on one outer surface.
[0148] Next, a method for fabricating the NRD guide S2 is described
with respect to an exemplary case where the dielectric strip 203 is
made of cordierite ceramics. First, a MgCO.sub.3 powder (purity of
99 percent or higher), an Al.sub.2O.sub.3 powder (purity of 99
percent or higher) and a SiO.sub.2 powder (purity of 99 percent or
higher) are measured to obtain a cordierite composition, and mixed.
A powder (purity of 99 percent or higher) of an oxide, carbonate,
nitride or the like of at least one kind of element selected from
Y, La, Ce, Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu is added to the
mixed powder. In this way, a sintering temperature range is
extended to make a resulting sintered material denser.
[0149] After being provisionally burnt at 1100 to 1300.degree. C.
in the air if necessary, this mixture is crushed into powder, a
suitable amount of an organic binder is added to the crushed powder
and a strip-shaped molded matter is formed by a press molding
method, a CIP molding method, a doctor blade method, a tape molding
method such as a rolling method, an excluding method, an injection
molding method or like known molding method. Thereafter, the molded
matter is treated to remove the binder therefrom at a specified
temperature in the air, sintered at 1300 to 1500.degree. C. in the
air, and has its outer surface ground if necessary. As a result,
strip-shaped ceramics, i.e., the dielectric strip can be
obtained.
[0150] If necessary, a metallic paste containing W (tungsten), Mo
(molybdenum), Cu, Ag, Pt, Au, or like metal as a main component and
obtained by adding a specified organic binder, a solvent, etc. to a
metal powder and kneading the resulting mixture is prepared for the
dielectric strip, applied to the upper and lower surfaces of the
dielectric strip by a known printing method such as a screen
printing method or a gravure printing method in such a manner as to
have a thickness of, e.g., 5 to 30 .mu.m, and is baked at a
temperature at or below 1200.degree. C.
[0151] After the dielectric strip coated with the metallic layers
is cut into a specified shape or has its metallic layers ground, it
is placed in a specified position of the parallel plate conductor
or held in a specified position between the parallel plate
conductors, and the aforementioned solder is heated to about 240 to
350.degree. C. to be melted, and is solidified to join the
dielectric strip and the parallel plate conductors. As a result,
the NRD guide can be fabricated. In the case that the metallic
layers are formed on the outer surfaces of the dielectric strip,
they are joined with the parallel plate conductors using the
solder. In order to control the spacing between the parallel plate
conductors to a specified value, the parallel plate conductors may
be pressurized during adhesion by the solder 204.
[0152] A method for forming the metallic layers is not limited to
the aforementioned so-called pressure film method. For instance, a
method for applying a metallic paste to the outer surface of the
molded matter and simultaneously sintering them, a method for
forming a metallic layer of, e.g., Ni/Cr, Au/Cr, Ag/Cu/Cr, Cu/Ti,
Ni/Ti or Pt/Ti on the outer surface of the dielectric strip by a
thin film forming method such as a deposition method, a spattering
method, or a CVD method, and a method for, after forming a metal
foil on the outer surface of a transfer film made of a resin,
transferring the metal foil onto the outer surface of the molded
matter may also be applicable. It should be noted that Ni/Cr,
Au/Cr, Ag/Cu/Cr, Cu/Ti, Ni/Ti or Pt/Ti means Cr layer formed on Ni
layer, Cr layer formed on Au layer, Cr layer formed on Cu layer
formed on Ag layer, Ti layer formed on Cu layer, Ti layer formed on
Ni layer, or Ti layer formed on Pt layer.
[0153] Next, an exemplary case where the dielectric strip is made
of glass ceramics is described. First, after a specified organic
binder, a solvent, etc. are added and mixed with ceramics powder
for forming the aforementioned filler and/or a glass powder
containing Si, Al, Mg, Zn, B, Ca or the like, a bar-shaped or
sheet-shaped matter is molded of this mixture by a press molding
method, a CIP (Cold Isostatic Press) molding method, a doctor blade
method, a tape molding method such as a rolling method, an
excluding method, an injection molding method or like known molding
method.
[0154] Further, a metallic layer having a thickness of 5 to 30
.mu.m is formed on the bar-shaped or sheet-shaped molded matter by
the aforementioned method. At this time, if the method for
transferring the metallic layer formed of a metal foil of Cu, Ag or
like metal onto the outer surface of the molded matter using the
transfer film is used, shrinkage of the molded matter in widthwise
direction can be suppressed to improve dimensional precision, a
time for grinding can be shortened, and the molded matter is
prevented from warping during sintering. As a result, dielectric
strips having a high dimensional precision can be
mass-produced.
[0155] After being treated to remove the binder, the molded matter
coated with the metallic layer is sintered at 800 to 1050.degree.
C., preferably at 830 to 950.degree. C. to obtain the dielectric
strip integrally formed with the metallic layer. The NRD guide can
be fabricated by arranging the thus obtained dielectric strip in a
specified position between the parallel plate conductors using the
solder similar to the above.
[0156] The NRD guide constructed as above can be suitably used in a
high-frequency band at or above 50 GHz, preferably at or above 60
GHz, and more preferably at or above 70 GHz.
EXAMPLE 2
[0157] A MgCO.sub.3 powder (purity of 99 percent or higher), an
Al.sub.2O.sub.3 powder (purity of 99 percent or higher) and a
SiO.sub.2 powder (purity of 99 percent or higher) were measured and
mixed. After being provisionally burnt at 1200.degree. C. for 2
hours in the air, this mixture was crushed, and granulates were
produced by adding a suitable amount of binder. These granulates
were press-molded at a pressure of 100 MPa to form a molded matter
having a diameter of 12 mm and a thickness of 8 mm. After being
treated to remove the binder at a specified temperature, the molded
matter was sintered at 1455.degree. C. for 2 hours.
[0158] A specified processing was applied to the thus obtained
sintered matter, and the dielectric constant and dielectric loss of
the sintered matter at 60 GHz were measured by a dielectric
resonator method using a network analyzer and a synthesized
sweeper. The measured dielectric constant and dielectric loss were
4.8, 2.times.10.sup.-4, respectively.
[0159] A molded matter was formed using the above granulates, and
treated to remove the binder at a specified temperature.
Thereafter, the molded matter was sintered at 1455.degree. C. for 2
hours. After the sintered matter was cut to form a dielectric strip
of 1.8 mm (height).times.0.8 mm (width).times.100 mm (length),
Pt/Ti metallic thin films were formed on the upper and lower
surfaces of the dielectric strip by forming a titanium film having
a thickness of 50 .mu.m and a platinum film having a thickness of
50 .mu.m thereon by spattering.
[0160] The dielectric strip was arranged in a specified position
between two parallel plate conductors made of copper and having a
longitudinal dimension of 80 mm, a lateral dimension of 80 mm and a
thickness of 2 mm. Spheres of a solder containing a Au--Sn alloy
were provided between the metallic thin films of the dielectric
strip and the parallel plate conductors and heated at 320.degree.
C. to form the NRD guide. As a result of a microscopic observation,
the solder had a maximum thickness of 0.1 mm and a smooth
surface.
[0161] The transmission loss of the obtained NRD guide at 76.5 GHz
measured by a network analyzer was 1 dB. The transmission loss
thereof was similarly measured after a heat cycle of -45 to
125.degree. C. was applied to it 1000 times. The measurement result
was 1 dB, and no adhesion problem such as peeling was found by
visual observation.
EXAMPLE 3
[0162] Glass ceramics material was prepared by adding ceramics
filler having an average particle diameter of 2 .mu.m to a glass
having an average particle diameter of 2 .mu.m and a composition as
defined below.
[0163] Glass: (44 weight percent of SiO.sub.2, 29 weight percent of
Al.sub.2O.sub.3, 11 weight percent of MgO, 7 weight percent of ZnO,
9 weight percent of B.sub.2O.sub.3)
[0164] Ceramic filler: 15 weight percent of SiO.sub.2, 10 weight
percent of ZnO in relative to 75 weight percent of glass.
[0165] A molded matter having a diameter of 12 mm and a thickness
of 8 mm was formed by adding a suitable amount of binder to the
mixed powder and press-molding the resulting powder at a pressure
of 100 MPa, and was treated to remove the binder at a specified
temperature. Thereafter, the molded matter was sintered at
1455.degree. C. for 2 hours to form glass ceramics. The dielectric
constant and dielectric loss of the sintered matter at 60 GHz were
similarly measured. The measured dielectric constant and dielectric
loss were 4.8, 8.times.10.sup.-4, respectively.
[0166] After a slurry was produced by adding an organic binder and
a solvent to the mixed powder and mixing them, a sheet-shaped
molded matter was formed by the doctor blade method.
[0167] On the other hand, after a transfer film coated with a
copper foil was placed such that the copper foil is adhered to the
outer surface of the sheet-shaped molded matter and was pressed at
40.degree. C. and 100 MPa, it is peeled off to obtain the molded
matter having a metallic layer made of the copper foil formed on
its outer surface.
[0168] After a treatment was made to remove the binder from the
molded matter coated with the copper foil, the molded matter was
sintered at 950.degree. C. and gold plating was applied to the
outer surface of the copper foil. Thereafter, the gold-plated
sintered matter was cut and ground to fabricate a dielectric strip
integrally formed with the metallic layer. The metallic layer of
the dielectric strip is connected in the same specified position of
the parallel plate conductors as in Example 2 using a solder, which
was then melted and solidified to secure the dielectric strip to
the parallel plate conductors as in Example 2, thereby fabricating
an NRD guide. The solder had a maximum thickness of 0.1 mm and a
smooth surface.
[0169] The obtained NRD guide was estimated substantially in the
similar manner as in Example 2. The estimation result showed that a
transmission loss was 2 dB, a transmission loss after application
of a heat cycle was 2 dB and no adhesion problem such as peeling
was found by visual observation.
EXAMPLE 4
[0170] A groove having a width of 0.8 mm, a depth of 0.2 mm and a
length of 100 mm was formed in a position of each parallel plate
conductor of Example 2 facing the dielectric strip, and the solder
of Example 2 was placed in the grooves. The dielectric strip of
Example 2 having a height of 1.8 mm was placed on the solder, and
an NRD guide was fabricated as in Example 2 except that the
parallel plate was formed with the groove.
[0171] The transmission loss of the obtained NRD guide was measured
substantially in the similar manner as in Example 2. The
measurement result showed that a transmission loss was 1 dB, a
transmission loss after application of a heat cycle as in Example 2
was 1 dB and no adhesion problem such as peeling was found by
visual observation.
COMPARATIVE EXAMPLE 1
[0172] An NRD guide was fabricated as in Example 2 except that a BT
resin was used instead of the solder of Example 2 and estimated.
Although a transmission loss was as low as 1 dB, peeling was found
between the adhesive and the dielectric strip by visual observation
after application of a heat cycle.
COMPARATIVE EXAMPLE 2
[0173] An NRD guide was fabricated as in Example 4 except that the
solder was not used. The depths of the grooves were adjusted such
that the spacing between the parallel plate conductors was equal to
the one of Example 3. A result of an estimation made as in Example
2 showed that a transmission loss was too high to be measured and
displacement had occurred during assembling.
[0174] Since the parallel plate conductors are formed so that the
arithmetic average roughness Ra of their inner surfaces satisfies
0.1 .mu.m.ltoreq.Ra.ltoreq.50 .mu.m as described above, the NRD
guides S2, S2a according to the second embodiment of the invention
have an excellent durability and can effectively suppress the
transmission loss of the high-frequency signal because the
dielectric strip is strongly secured to the inner surfaces of the
parallel plate conductors by the solder.
[0175] Further, since the parallel plate conductors and the
dielectric strip are joined using the solder in the NRD guides S2,
S2a, the dielectric strip can be precisely positioned. As a result,
the transmission loss of the signal can be reduced and excellent
heat resistance, durability and reliability can be ensured.
[0176] In the case that the dielectric strip 203 of the NRD guide
S2, S2a is made of, e.g., ceramics, it may be comprised of a
plurality of strip sections as in the first embodiment shown in
FIG. 1 and the end faces of the respective strip sections may be
opposed to each other at a spacing equal to or shorter than 1/8 of
the wavelength of the high-frequency signal to be transmitted. This
can reduce conversion of electromagnetic waves of the LSM mode into
those of the LSE mode and enables an easy fabrication of a
dielectric strip having a complicated shape formed by linear and
curved portions. In other words, if the dielectric strip 203 is
formed by a plurality of strip sections, a bend loss can be reduced
even if the dielectric strip 203 includes a curved portion.
[0177] FIG. 5 is a schematic section showing an NRD guide according
to a third embodiment of the invention. An NRD guide S3 according
to the third embodiment is mainly designed to solve the problems in
the prior art. In FIG. 5, the NRD guide S3 is constructed by
arranging a dielectric strip 303 as a waveguide strip and a
dielectric strip 304 as a suppressor strip forming a mode
suppressor between a pair of parallel plate conductors 301, 302
vertically opposed to each other at a spacing which is equal to or
shorter than half the wavelength of a high-frequency signal to be
transmitted. It should be noted that the wavelength here is a
wavelength in the air (free space) at an operating frequency.
[0178] The respective parallel plate conductors 301, 302 are formed
of conductive plates made of, e.g., Cu, Al, Fe, SUS (Stainless
Steel), Ag, Au, Pt since they need to have a high electric
conductivity and an excellent processability. Alternatively, they
may be formed of insulating plates made of ceramics, resin or like
material having a conductive layer made of the above metallic
materials formed on its outer surface. Further, the surfaces (inner
surfaces) of the parallel plate conductors 301, 302 facing the
dielectric strips 303, 304 are ground so that an arithmetic average
roughness Ra thereof satisfies 0.1 .mu.m.ltoreq.Ra.ltoreq.50
.mu.m.
[0179] This arithmetic average roughness Ra is the same as the one
defined in the first embodiment, and the range thereof is set as
above for the same reason mentioned in the first embodiment. The
arithmetic average roughness Ra satisfies preferably 0.3
.mu.m.ltoreq.Ra.ltoreq.25 .mu.m, and more preferably 0.4
.mu.m.ltoreq.Ra.ltoreq.10 .mu.m.
[0180] The dielectric strip 303 as a waveguide strip may be made of
a resin dielectric material such as Teflon, polystyrene or glass
epoxy or ceramic such as cordierite, alumina, glass ceramics or
forsterite. However, in view of a dielectric characteristic,
processability, strength, miniaturization, reliability, etc., the
dielectric strip 303 is desirably made of cordierite ceramics. By
containing at least one kind of element selected from Y, La, Ce,
Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu in the cordierite ceramics,
electric characteristics such as a Q-value can be improved and
signals can be transmitted with a low transmission loss.
[0181] The dielectric strip 304 as a suppressor strip forming a
mode suppressor is made of ceramics and is continuously arranged at
one end of the dielectric strip 303. In the following description,
the dielectric strip 304 is referred to as ceramics dielectric
strip 304. The ceramic dielectric strip 304 may be spaced apart
from one end of the dielectric strip 303 by a specified
distance.
[0182] A conductive layer 305 of a specified pattern is so formed
inside, particularly at the center of the ceramic dielectric strip
304 as to extend perpendicularly to the parallel plate conductors
301, 302. A mode suppressor (hereinafter, merely "suppressor") 306
for the NRD guide is formed by the ceramic dielectric strip 304 and
the conductive layer 305.
[0183] Although the conductive layer 305 is arranged to extend
perpendicularly to the parallel plate conductors 301, 302 to form
the suppressor for suppressing transmission of the LSE mode in FIG.
5, the third embodiment is not limited thereto. For example, the
suppressor may suppress transmission of the LSM mode by arranging
the conductive layer 305 parallel to the parallel plate conductors
301, 302.
[0184] An essential feature of the third embodiment lies in that
the ceramic dielectric strip 304 and the conductive layer 305
forming the suppressor 306 are integrally formed by simultaneously
sintering. This eliminates a possibility of creating a portion
having a different dielectric constant such as a clearance between
the ceramic dielectric strip 304 and the conductive layer 305 and
can improve the dimensional precision of the suppressor 306 and the
precision of positioning of the conductive layer 305. Therefore, an
NRD guide which stably operates within an operation band while
being only slightly variable from the one as designed can be
realized.
[0185] Cordierite, alumina, glass ceramics, forsterite or like
material can be used as the ceramic dielectric strip 304. Since the
conductive layer 305 is desirably made of a low-resistance metal
such as copper, silver or gold, the ceramic dielectric strip 304 is
desirably made of glass ceramics which enables simultaneous
sintering in the case that a low-resistance metal is used. Further,
the glass ceramics is desirably such that at least one kind of SiO2
crystal phases, spinel type crystal phases such as
MgAl.sub.2O.sub.4, ZnAl.sub.2O.sub.4, diopside type oxide crystal
phases such as Ca(Mg, Al) (Si, Al).sub.2O.sub.6, and other similar
crystal. phases such as Ca.sub.2MgSi.sub.2O.sub.7 (akermanite),
CaMgSiO.sub.4 (monticellite), Ca.sub.3MgSi.sub.2O8 (merwinite),
ilmenite type crystal phases such as MgTiO.sub.3, SrTiO.sub.3,
BaTiO.sub.3, CaTiO.sub.3 and (Mg, Zn)TiO.sub.3, willemite type
crystal phases such as Zn.sub.2SiO.sub.4, MgSiO.sub.3,
3Al.sub.2O.sub.3.2SiO.sub.2 and Mg.sub.2Al.sub.4Si.sub.5O.sub.18
having a small dielectric loss is precipitated therefrom. It is
also desirable that the glass ceramics contains a silica having a
small dielectric loss as a main component beside the above crystal
phases.
[0186] Further, ZnO, Al.sub.2O.sub.3, MgAl.sub.2O.sub.4, MgO,
TiO.sub.2, ZrO.sub.2, CaZrO.sub.3 and the like may be dispersed as
a filler in the glass ceramics in addition to the aforementioned
crystal phases.
[0187] It is also desirable that the dielectric constant of. the
ceramic dielectric strip 304 approximates to that of the dielectric
strip 303, particularly a difference thereof lies .+-.1. For
example, if the dielectric strip 303 is made of cordierite ceramics
having a dielectric constant of 4.8, the ceramic dielectric strip
304 is optimally made of glass ceramics containing a silica glass
phase or a ZnAl.sub.2O.sub.4 or MgSiO.sub.3 crystal phase or like
crystal phase and having a dielectric constant of 4.7 to 4.9.
[0188] The conductive layer 305 is arranged in a transmission
direction of a signal along the longitudinal center of the ceramic
dielectric strip 304, and a pattern in which two different sections
having widths W1, W2 (W1>W2) and a length L which is 1/4 of the
wavelength of a TEM wave are repeated as shown in FIG. 6 can be
suitably adopted as the shape of the conductive layer 305. It
should be noted that W denotes a width of the ceramic dielectric
strip 304.
[0189] An other end of the suppressor 306 is connected with a
device such as a circulator, an oscillator or a mode converter
(none of these devices is shown) where the LSE mode is created or
may be connected with a bent dielectric strip of NRD guide if
necessary.
[0190] Next, a method for fabricating the suppressor 306 is
described with respect to an exemplary case where the dielectric
strip 303 as a waveguide strip is made of cordierite ceramics and
the ceramic dielectric strip 304 as a suppressor strip is made of
glass ceramics. First, the dielectric strip 303 is fabricated, for
example, by the following method. A MgCO.sub.3 powder (purity of 99
percent or higher), an Al.sub.2O.sub.3 powder (purity of 99 percent
or higher) and a SiO.sub.2 powder (purity of 99 percent or higher)
are measured to obtain a cordierite composition, and mixed. A
powder (purity of 99 percent or higher) of an oxide, carbonate,
nitride or the like of at least one kind of element selected from
Y, La, Ce, Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu is added to the
mixed powder. In this way, a sintering temperature range is
extended to make a resulting sintered material denser.
[0191] After being provisionally burnt at 1100 to 1300.degree. C.
in the air if necessary, this mixture is crushed into powder, a
suitable amount of an organic binder is added to the crushed powder
and a strip-shaped molded matter is formed, for example, by a press
molding method, a CIP molding method, a doctor blade method, a tape
molding method such as a rolling method, an excluding method, an
injection molding method or like known molding method. Thereafter,
the molded matter is treated to remove the binder therefrom at a
specified temperature in the air, sintered at 1300 to 1500.degree.
C. in the air, and has its outer surface ground if necessary. As a
result, the dielectric strip 303 can be obtained.
[0192] Next, a method for fabricating the suppressor 306 is
described. First, after a specified organic binder, a solvent, etc.
are added and mixed with ceramics powder and/or a glass powder
containing Si, Al, Mg, Zn, B, Ca or the like for forming the
aforementioned filler, a column-shaped or sheet-shaped matter is
molded of this mixture, for example, by a press molding method, a
CIP molding method, a doctor blade method, a tape molding method
such as a rolling method, an excluding method, an injection molding
method or like known molding method.
[0193] On the other hand, a conductive paste obtained by mixing and
kneading a specified organic binder, a solvent and the like with a
conductive powder is prepared and applied to the outer surface of
the molded matter by a known printing method such as a screen
printing method or a gravure printing method in such a manner as to
have a thickness of, e.g., 5 to 30 .mu.m.
[0194] An other molded matter is formed similar to the above molded
matter and is so placed as to cover a pattern forming surface of
the molded matter to which the conductive paste was applied,
thereby obtaining a laminated matter. The laminated matter can also
be obtained by a known multiple layer method of ceramics green
sheet. Thereafter, the laminated matter is cut or ground into a
specified shape after being sintered at a specified temperature. In
this way, the ceramic dielectric strip having a conductive layer
inside, i.e., the suppressor 306 can be obtained.
[0195] A method for forming the conductive layer is not limited to
the aforementioned printing method. For example, if it is formed by
a thin film method such as a deposition method, a spattering method
or a CVD method using a mask of a specified pattern, the
dimensional precision of the conductive layer pattern can be
improved. Alternatively, a method for etching a metal foil in a
specified pattern after forming it on a transfer sheet made of a
resin, and transferring the metal foil pattern onto the outer
surface of the molded matter may also be applied. According to this
method, there can be formed a conductive layer pattern which is
hardly subject to any change in the dimensions of the conductive
layer even-by sintering of the molded matter and also having a high
dimensional precision.
[0196] By arranging the thus obtained ceramic dielectric strip, for
example, in a-position continuous with or spaced apart by a
specified distance from the dielectric strip between the pair of
parallel plate conductors, an NRD guide having excellent
characteristics can be easily obtained.
[0197] In the case that the ceramic dielectric strip is made of a
cordirite ceramics or aluminaceramics, the conductive layer may be
formed of a high-melting point metal such as tungsten (W),
molybdenum (Mo) or of a metal obtained by adding a high-melting
point metal such as tungsten (W), molybdenum (Mo) to copper (Cu).
The suppressor made of such a material can be suitably used in a
high-frequency band above 50 GHz, particularly above 60 GHz, and
further above 70 GHz.
EXAMPLE 5
[0198] A MgCO.sub.3 powder (purity of 99 percent or higher), an
Al.sub.2O.sub.3 powder (purity of 99 percent or higher) and a
SiO.sub.2 powder (purity of 99 percent or higher) were measured and
mixed. After being provisionally burnt at 1200.degree. C. for 2
hours in the air, this mixture was crushed, and granulates were
produced by adding a suitable amount of binder. These granulates
were press-molded at a pressure of 100 MPa to form a molded matter
having a diameter of 12 mm and a thickness of 8 mm. After being
treated to remove the binder at a specified temperature, the
molded-matter was sintered at 1455.degree. C. for 2 hours.
[0199] The dielectric constant and dielectric loss of the obtained
sintered matter at 60 GHz were measured by a dielectric resonator
method using a network analyzer and a synthesized sweeper. The
measurement result is shown in TABLE-2.
[0200] A molded matter having a width of 3 mm, a thickness of 2 mm
and a length of 120 mm was formed using the above granulates, and
treated to remove the binder at a specified temperature.
Thereafter, the molded matter was sintered at 1455.degree. C. for 2
hours, thereby forming a waveguide strip.
[0201] On the other hand, materials of glass ceramics A, B were
prepared by adding ceramics filler having an average particle
diameter of 1.5 to 2.5 .mu.m to a glass having an average particle
diameter of 1.5 to 2.5 .mu.m and a composition as defined
below.
[0202] Glass Ceramics A
[0203] Glass: 44 weight percent of SiO.sub.2, 29 weight percent of
Al.sub.2O.sub.3, 11 weight percent of MgO, 7 weight percent of ZnO,
9 weight percent of B.sub.20.sub.3
[0204] Ceramic filler: 15 weight percent of SiO.sub.2, 10 weight
percent of ZnO in relative to 75 weight percent of glass
[0205] Glass Ceramics B
[0206] Glass: 44 weight percent of SiO.sub.2, 29 weight percent of
Al.sub.2O.sub.3, 11 weight percent of MgO, 7 weight percent of ZnO,
9 weight percent of B.sub.2O3
[0207] Ceramic filler: 25 weight percent of ZnO in relative to 75
weight percent of glass
[0208] A molded matter having a diameter of 12 mm and a thickness
of 8 mm was formed by adding a suitable amount of binder to the
mixed powder and press-molding the resulting powder at a pressure
of 100 MPa, and was treated to remove the binder at a specified
temperature. Thereafter, the molded matter was sintered at 850 to
1000.degree. C. for 2 hours to form the glass ceramics A, B. The
dielectric constant and dielectric loss of the glass ceramics A, B
at 60 GHz were measured in a manner similar to the above. The
measurement result is shown in TABLE-2.
[0209] After a slurry was produced by adding an organic binder and
a solvent to the mixed powder and mixing them, a sheet was formed
by the doctor blade method. Thereafter, a conductive layer of a
specified pattern as shown in FIG. 6 having an attenuation
characteristic of 30 dB or higher at 76.5 GHz was formed on the
outer surface of the sheet by a technique listed in TABLE-2, and an
other sheet formed as above was placed on the outer surface of the
former sheet.
[0210] After being sintered at 850 to 1000.degree. C. in a
nonoxiding atmosphere, the obtained laminated matter was cut into a
specified shape, thereby forming the suppressor strip.
[0211] The obtained waveguide strip was cut to a height of 1.8 mm,
a width of 1 mm and a length of 100 mm, whereas the obtained
suppressor strip was cut to a height of 1.8 mm, a width of 1 mm and
a length of 10 mm. They were arranged between parallel plate
conductors made of two copper plates having a longitudinal
dimension of 100 mm, a lateral dimension of 100 mm and a thickness
of 8 mm, electromagnetic waves excited in the LSM mode were
inserted into the suppressor after being converted into those of
the LSE mode. An output strength (transmission loss at 76.5 GHz) of
the LSE mode outputted from the suppressor was measured by a
network analyzer to obtain an attenuation characteristic of the LSE
mode. The result is shown in TABLE-2.
EXAMPLE 6
[0212] An NRD guide was formed as in Example 5 except that the
dielectric strip was made of glass ceramics used for the suppressor
strip of Example 5 (sample No. 5) and the suppressor strip is made
of cordierite ceramics used for the waveguide strip in Example 5
and the conductive layer therein was formed of tungsten (W) (sample
No. 6), and estimated. The result is shown in TABLE-2.
COMPARATIVE EXAMPLE 3
[0213] An NRD guide was fabricated as in Example 5 except that two
sintered matters having substantially the same shape which would be
obtained by vertically dividing the suppressor strip made of
cordierite ceramics of the sample No. 6 of Example 6 were formed,
and were so arranged in parallel to each other as to cover a copper
conductive layer formed on one outer surface of one sintered matter
by deposition or were adhered to each other by a polyvinyl alcohol
adhesive, and estimated (samples No. 7, 8). In this case, the
conductive layer was arranged to be located in the middle. The
result is shown in TABLE-2.
COMPARATIVE EXAMPLE 4
[0214] An NRD guide was fabricated similar to the sample No. 8
except that the suppressor strip of the sample No. 8 of Comparative
Example 3 was made of a glass-epoxy resin composite material and
half pieces were adhered by an adhesive, and estimated (sample No.
9). The result is shown in TABLE-2.
2 TABLE 2 NRD Guide Strip Suppressor Strip Conductive Layer
Suppressor LSE Mode Material D.C. D.L. Material D.C. D.L. Material
F.M. F.M. A.C. (dB) 1 Cordierite 4.8 3.6 .times. 10.sup.-4 Glass
4.8 8 .times. 10.sup.-4 Cu Printing Simultaneous 30 Ceramics A
Sintering 2 Cordierite 4.8 3.6 .times. 10.sup.-4 Glass 4.8 8
.times. 10.sup.-4 Cu Deposition Simultaneous 35 Ceramics A
Sintering 3 Cordierite 4.8 3.6 .times. 10.sup.-4 Glass 4.8 8
.times. 10.sup.-4 Cu Transfer Simultaneous 35 Ceramics A Sintering
4 Cordierite 4.8 3.6 .times. 10.sup.-4 Glass 5.5 9.5 .times.
10.sup.-4 Cu Deposition Simultaneous 28 Ceramics B Sintering 5
Glass 4.8 8 .times. 10.sup.-4 Glass 4.8 8 .times. 10.sup.-4 Cu
Deposition Simultaneous 32 Ceramics Ceramics A Sintering A 6
Cordierite 4.8 3.6 .times. 10.sup.-4 Cordierite 4.8 3.6 .times.
10.sup.-4 W Printing Simultaneous 25 Sintering *7 Cordierite 4.8
3.6 .times. 10.sup.-4 Cordierite 4.8 3.6 .times. 10.sup.-4 Cu
Deposition Parallel 8 Arrangement *8 Cordierite 4.8 3.6 .times.
10.sup.-4 Cordierite 4.8 3.6 .times. 10.sup.-4 Cu Deposition With
Adhesive 13 *9 Cordierite 4.8 3.6 .times. 10.sup.-4 Glass-Epoxy 4.8
100 .times. 10.sup.-4 Cu Deposition With Adhesive 15
[0215] As is clear from the results shown in TABLE-2, the
suppressors formed by arranging the two sintered half pieces in
parallel to each other (sample No. 7) or adhering them by the
adhesive (samples Nos. 8 and 9) had a low performance as a
suppressor: a LSE mode attenuation characteristic of 10 dB or lower
because of a clearance formed between the two sintered half pieces
or the adhesive therebetween. Further, a microscopic observation
confirmed the presence of air bubbles in the adhesive.
[0216] Contrary to this, the inventive suppressors (samples Nos. 1
to 6) integrally formed by simultaneous sintering showed a
satisfactory suppressor characteristic: a LSE mode attenuation
characteristic of 25 dB or higher.
[0217] Since the parallel plate conductors are formed so that the
arithmetic average roughness Ra of their inner surfaces satisfies
0.1 .mu.m s Ra s 50 .mu.m as described above, the NRD guide S3
according to the third embodiment of the invention has an excellent
durability and can effectively suppress the transmission loss of
high-frequency signals because the dielectric strip is strongly
secured to the inner surfaces of the parallel plate conductors.
[0218] Further, since the suppressor is obtained by integrally
forming the ceramic dielectric strip and the conductive layer by
simultaneous sintering in the NRD guide S3, the dimensional
precision of the suppressor and the precision of positioning of the
conductive layer can be improved and the suppressor can be easily
formed and have a stable function.
[0219] In the case that the dielectric strip 303 of the NRD guide
S3 is made of, e.g., ceramics, it may be comprised of a plurality
of strip sections as in the first embodiment shown in FIG. 1 and
the end faces of the respective strip sections may be opposed to
each other at a spacing equal to or shorter than 1/8 of the
wavelength of the high-frequency signal to be transmitted. This can
reduce conversion of electromagnetic waves of the LSM mode into
those of the LSE mode and enables an easy fabrication of a
dielectric strip having even a complicated shape formed by linear
and curved portions. In other words, if the dielectric strip 303 is
formed by a plurality of strip sections, a bend loss can be reduced
even if the dielectric strip 303 includes a curved portion.
[0220] FIG. 7 is a schematic perspective view partly cut away and
partly in section showing an NRD guide according to a fourth
embodiment of the invention. An NRD guide S4 according to the
fourth embodiment is mainly designed to solve the problems in the
prior art. In FIG. 7, the NRD guide S4 is constructed by arranging
a dielectric strip 403 as a waveguide strip and a dielectric strip
404 as a suppressor strip forming a suppressor between a pair of
parallel plate conductors 401, 402 vertically opposed to each other
at a spacing which is equal to or shorter than half the wavelength
of a high-frequency signal to be transmitted. It should be noted
that the wavelength here is a wavelength in the air (free space) at
an operating frequency.
[0221] The respective parallel plate conductors 401, 402 are formed
of conductive plates made of, e.g., Cu, Al, Fe, SUS (Stainless
Steel), Ag, Au, Pt, brass (Cu--Zn alloy) since they need to have a
high electric conductivity and an excellent processability.
Alternatively, they may be formed of insulating plates made of
ceramics, resin or like material having a conductive layer made of
the above metallic materials formed on its outer surface. Further,
the surfaces (inner surfaces) of the parallel plate conductors 401,
402 facing the dielectric strips 403, 404 are ground so that an
arithmetic average roughness Ra thereof satisfies 0.1
.mu.m.ltoreq.Ra.ltoreq.50 .mu.m.
[0222] This arithmetic average roughness Ra is the same as the one
defined in the first embodiment, and the range thereof is set as
above for the same reason mentioned in the first-embodiment. The_
arithmetic average roughness Ra satisfies preferably 0.3
.mu.m.ltoreq.Ra.ltoreq.25 .mu.m, and more preferably 0.4
.mu.m.ltoreq.Ra.ltoreq.10 .mu.m.
[0223] The dielectric strip 403 as a waveguide strip may be made of
a resin dielectric material such as Teflon, polystyrene or glass
epoxy or a cordierite (2MgO.2Al.sub.2O.sub.3.5SiO.sub.2) ceramics,
alumina (Al.sub.2O.sub.3) ceramics, glass ceramics or forsterite
(2MgO.SiO.sub.2) ceramics or like ceramics having a low dielectric
constant. This is because these materials can suppress a
transmission loss in a high-frequency band. Particularly in view of
a dielectric characteristic, processability, strength,
miniaturization, reliability, etc., the dielectric strip 403 is
desirably made of cordierite ceramics. By containing at least one
kind of element selected from Y, La, Ce, Pr, Nd, Sm, Eu, Dy, Ho,
Er, Tm, Yb, Lu in the cordierite ceramics, electric characteristics
such as a Q-value can be improved and signals can be transmitted
with a low transmission loss.
[0224] The dielectric strip 404 as a suppressor strip forming a
suppressor is made of, e.g., the same material as the dielectric
strip 303, and is continuously arranged at one end of the
dielectric strip 403. The ceramic dielectric strip 404 may be
spaced apart from one end of the dielectric strip 403 by a
specified distance. Conductive layers 405 of a specified pattern to
be described later are formed inside, particularly at the center of
the ceramic dielectric strip 404, and a suppressor 406 for the NRD
guide is formed by the ceramic dielectric strip 404 and the
conductive layer 405.
[0225] The conductive layers 405 are made of Cu, Al, Fe, SUS
(stainless steel), Ag, Au, Pt or like material having a high
electric conductivity, and is arranged substantially in a widthwise
middle position of the dielectric strip 404 in a plane
perpendicular to the principle planes of the parallel plate
conductors 401, 402 and parallel to a transmission direction of
high-frequency signals. Although the suppressor for suppressing
transmission of the LSE mode is constructed in this manner, the
present invention is not limited thereto. For example, a suppressor
for suppressing transmission of the LSE mode may be formed by
arranging the conductive layers 405 parallel to the parallel plate
conductors 401, 402.
[0226] Each conductive layer 405 has a vertically long rectangular
shape, and a plurality of conductive layers 405 are arranged in the
transmission direction of the high-frequency signal. The conductive
layers 405 may take any other shape such as a square, circle or
ellipse, but are preferably vertically symmetrical. The number of
the conductive layers 405 (suppressing stages) is preferably
between 3 and 10 in order to effectively attenuate unnecessary
modes. If the number of the conductive layers 405 exceeds 10, the
suppressor 406 becomes too long, thereby making the NRD guide
larger and making the transmission loss of the high-frequency
signal likely to increase.
[0227] A dimension b (see FIG. 8) of each conductive layer 405 in
the transmission direction of the high-frequency signal is
preferably 1/2 or less of the wavelength of a TEM mode
electromagnetic wave of the high-frequency signal, and the
thickness thereof is preferably 0.1 mm or smaller. If the dimension
b of the conductive layer 405 exceeds half the wavelength of the
TEM mode electromagnetic wave of the high-frequency signal, it
becomes difficult to suppress the TEM mode by attenuation. A lower
limit of the dimension b of the conductive layer 405 is not
particularly limited, but is preferably 0.1 mm or longer for a
practical reason. If the thickness of the conductive layer 405
exceeds 0.1 mm, the electromagnetic waves of the LSE mode are
likely to be reflected, thereby increasing their transmission loss.
More preferably, the thickness of the conductive layer 405 is 0.05
.mu.m or larger. If it is below 0.05 .mu.m, it is difficult to form
the conductive layer 405 into a specified shape. An interval d (see
FIG. 8) between adjacent conductive layers 405 is desirably 1/4 or
shorter of the wavelength of the LSM mode in terms of transmission
characteristic, but the suppressor 406 is usable even if the
interval d exceeds 1/4 of the wavelength of the LSM mode.
[0228] The conductive layers 405 forming the suppressor 406 are
formed by a method for applying a metallic paste containing
metallic particles of, e.g., Cu by printing and sintering the
applied metallic paste or an other known thin film forming method
such as a deposition method, a spattering method or a CVD method.
Alternatively, the conductive layers 405 may be formed of thin
conductive plates and adhered to the inner surfaces of half pieces
of the dielectric strip 404 divided in a direction normal to the
transmission direction of the high-frequency signal or may be
inserted into a groove formed in the dielectric strip 404. The thus
formed dielectric strip 404 may be placed on the parallel plate
conductor 401 while being positioned with respect to the dielectric
strip 403 or may be placed on the parallel plate conductor 401
after being adhered to the dielectric strip 403 by an adhesive.
[0229] In the NRD guide in which the conductive layers 405 are
formed of thin conductive plates and inserted into the groove
formed in the dielectric strip 404, the dielectric strips 403, 404
may be integrally formed without being separated. In other words,
in either construction of the NRD guide, it is sufficient to form a
suppressor by providing a plurality of conductor layers at
specified intervals (repeating intervals) along the transmission
direction of the high-frequency signal in a plane parallel to the
transmission direction of the high-frequency signal inside the end
of the dielectric strip provided between the pair of parallel plate
conductors.
[0230] The suppressor 406 of the NRD guide S4 according to the
fourth embodiment is provided at a side of the dielectric strip 403
toward a mode converting device such as a circulator or an
oscillator at which side unnecessary modes including the LSE mode
are likely to be created. The high-frequency band in the present
invention corresponds to a microwave band and a millimeter wave
band ranging from in the order of 10 to in the order to 100 GHz,
and the NRD guide S4 according to the fourth embodiment is suitably
used in a high-frequency band, for example, above 30 GHz,
particularly above 50 GHz, and further above 70 GHz.
[0231] The NRD guide S4 according to the fourth embodiment is used
in a wireless LAN or a millimeter wave radar installed in an
automotive vehicle with a high-frequency diode such as a Gunn diode
incorporated thereinto as a high frequency generating device. In
such a millimeter wave radar, a millimeter wave is projected to an
obstacle and other automotive vehicles present around an automotive
vehicle in which this radar is installed, the reflected wave is
combined with the original millimeter wave to obtain a beat signal
(intermediate-frequency signal), and distances to the obstacle and
other automotive vehicles and their moving speeds are measured by
analyzing this beat signal.
[0232] The NRD guide S4 according to the fourth embodiment can
effectively attenuate unnecessary modes by suppressing the
resonance thereof since being provided with the suppressor 406 at
one end of the dielectric strip. Further, reflection by the
conductive layer of the LSM mode which is one of the transmission
modes is unlikely to occur in the NRD guide S4. Thus, the
transmission loss of the LSM mode can be reduced.
[0233] In the case that the dielectric strip 403 of the NRD guide
S4 is made of, e.g., ceramics, it may be comprised of a plurality
of strip sections as in the first embodiment shown in FIG. 1 and
the end faces of the respective strip sections may be opposed to
each other at a spacing equal to or shorter than .lambda./8
(.lambda. is a wavelength of a high-frequency signal to be
transmitted). This can reduce conversion of electromagnetic waves
of the LSM mode into those of the LSE mode and enables an easy
fabrication of a dielectric strip having even a complicated shape
formed by linear and curved portions. In other words, if the
dielectric strip 403 is formed by a plurality of strip sections, a
bend loss can be reduced even if the dielectric strip 403 includes
a curved portion.
[0234] A millimeter wave radar module as a millimeter wave
transmitting/receiving apparatus to which the NRD guide S4 is
applied is described below. FIGS. 9 to 12 show millimeter wave
radar modules according to the embodiment of the invention, wherein
FIG. 9A is a plan view of a millimeter wave radar module having an
integrated transmitting/receiving antenna, FIG. 10A is a plan view
of a millimeter wave radar module having independent transmitting
antenna and receiving antenna, FIG. 11 is a perspective view
showing a millimeter wave signal oscillator, and FIG. 12 is a
perspective view of a circuit board on which a variable-capacitance
diode (varactor diode) for the millimeter wave signal oscillator is
provided.
[0235] Identified by 410, 411 in FIG. 9A are a pair of vertically
arranged parallel plate conductors which are constructed similar to
the parallel plate conductors 401, 402 shown in FIG. 7. Various
devices to be described later are inserted between the pair of
parallel plate conductors 410, 411. It should be noted that the
upper parallel plate conductor 411 is partly cut away in order to
make an entire construction visible. Identified by 412 is a
millimeter wave oscillator of voltage control type which is
provided at one end of a first dielectric strip 413 to be described
later. The millimeter wave signal oscillator 412 outputs a
frequency-modulated millimeter wave signal to be transmitted by
cyclically controlling a bias voltage of the variable-capacitance
diode disposed in vicinity of the high-frequency diode
(high-frequency generating device) to have a triangular wave, a
sine wave or other wave such that a bias voltage applying direction
coincides with a direction of an electric field of a high-frequency
signal.
[0236] The first dielectric strip 413 is formed similar to the
dielectric strip 403 shown in FIG. 7 and is adapted to transmit the
millimeter wave signal obtained by modulating the high-frequency
signal outputted from the high-frequency diode such as a Gunn diode
as a high-frequency generating device. A first suppressor 414
formed similar to the suppressor 406 shown in FIG. 7 is connected
with one end of the dielectric strip 413. In other words, the NRD
guide S4 is substantially constructed by arranging the first
suppressor 414 at one end of the dielectric strip 413 provided
between the pair of parallel plate conductors 410, 411.
[0237] The first dielectric strip 413 has one end thereof connected
with the millimeter wave signal oscillator 412 via the first
suppressor 414 and the other end thereof connected with a mixer
415. Identified by 416 is a circulator made of two ferrite disks
which are ferromagnetic plates vertically opposed to each other and
having first, second and third connecting portions (none of them is
shown) each having one end thereof connected with a corresponding
one of second, third and fourth suppressors 417, 418, 419 formed
similar to the suppressor 406 shown in FIG. 7. In other words, the
second suppressor 417 is connected with the first connecting
portion of the circulator 416, the third suppressor 418 is
connected with the second connecting portion thereof and the fourth
suppressor 419 is connected with the third connecting portion
thereof.
[0238] Identified by 420 is a second dielectric strip having one
end thereof connected with the other end of the second suppressor
417. The second dielectric'strip 420 is adapted to transmit a
millimeter wave signal and is formed similar to the dielectric
strip 403 shown in FIG. 7. In other words, the NRD guide S4 is
substantially constructed by arranging the second suppressor 417 at
one end of the second dielectric strip 420 provided between the
pair of parallel plate conductors 410, 411. Identified by 421 is a
nonreflective termination (terminator) provided at the other end of
the second dielectric strip 420. The nonreflective termination 421
is provided with a resistance film 421a therein, as shown in FIG.
9B. The resistance film 421a is formed along a plane separating the
nonreflective termination 421 into an upper half and a lower half
and parallel with the pair of parallel plate conductors 410, 411.
Further, the resistance film 421a may be formed on side surfaces or
end surface of the nonreflective termination 421. The resistance
film 421a is made of an NiCr alloy or resin containing conductive
particles such as carbon particles. The nonreflective termination
421 provided with the resistance film 421a may be integrally formed
with the second dielectric strip 420 by simultaneous sintering.
[0239] Identified by 422 is a third dielectric strip having one end
thereof connected with the other end of the third suppressor 418.
The third dielectric strip 422 is adapted to transmit a millimeter
wave signal and is formed similar to the dielectric strip 403 shown
in FIG. 7. In other words, the NRD guide S4 is substantially
constructed by arranging the third suppressor 418 at one end of the
third dielectric strip 422 provided between the pair of parallel
plate conductors 410, 411. The leading end of the third dielectric
strip 422 is tapered to form a transmitting/receiving antenna
423.
[0240] Identified by 424 is a fourth dielectric strip having one
end thereof connected with the other end of the fourth suppressor
419. The fourth dielectric strip 424 is formed similar to the
dielectric strip 403 shown in FIG. 7. In other words, the NRD guide
S4 is substantially constructed by arranging the fourth suppressor
419 at one end of the fourth dielectric strip 424 provided between
the pair of parallel plate conductors 410, 411. The fourth
dielectric strip 424 transmits a radio wave received by the
transmitting/receiving antenna 423 and outputted from the third
connecting portion of the circulator 416 via the third dielectric
strip 422 to the mixer 415.
[0241] Here, part of the millimeter wave signal outputted from the
millimeter wave signal oscillator 412 is transmitted to the
circulator 416 by arranging one end of the first dielectric strip
413 toward the millimeter wave signal oscillator 412 and one end of
the second dielectric strip 420 close to each other for
electromagnetic coupling or joining one end of the first dielectric
strip 413 with one end of the second dielectric strip 420.
[0242] The mixer 415 mixes part of the millimeter wave signal
outputted from the millimeter wave signal oscillator 412 with the
received wave to generate an intermediate-frequency signal by
electromagnetically coupling an intermediate position of the first
dielectric strip 413 and that of the fourth dielectric strip 424 by
bringing them closer to each other or joining them.
[0243] In the construction of FIG. 9A, a pulsated millimeter wave
signal can be oscillated by providing a switch constructed similar
to the one shown in FIG. 12 in an intermediate position of the
first dielectric strip 413. A switch shown in FIG. 12 is
constructed such that a second choke-type bias supply strip 463 is
formed on one principle plane of a circuit board 461 and a PIN
diode or Schottky barrier diode of beam lead type is mounted, in an
intermediate position of the strip 463 by soldering.
[0244] Another embodiment of the millimeter wave radar module as an
inventive millimeter wave transmitting/receiving apparatus to which
the NRD guide S4 is applied is of the type shown in FIG. 10A having
independent transmitting antenna and receiving antenna. Identified
by 430, 431 in FIG. 10A are a pair of vertically arranged parallel
plate conductors which are constructed similar to the parallel
plate conductors 401, 402 shown in FIG. 7. It should be noted that
the, upper parallel plate conductor 431 is partly cut away in order
to make an entire construction visible.
[0245] Identified by 432 is a millimeter wave oscillator of voltage
control type which is provided at one end of a first dielectric
strip 433 to be described later. The millimeter wave signal
oscillator 432 outputs a frequency-modulated millimeter wave signal
to be transmitted by cyclically controlling a bias voltage of the
variable-capacitance diode disposed in vicinity of the
high-frequency diode (high-frequency, generating device) to have a
triangular wave, a sine wave or other wave such that a bias voltage
applying direction coincides with a direction of an electric field
of a high-frequency signal.
[0246] The first dielectric strip 433 is formed similar to the
dielectric strip 403 shown in FIG. 7 and is adapted to transmit the
millimeter wave signal obtained by modulating the high-frequency
signal outputted from the high-frequency diode such as a Gunn diode
as a high-frequency generating device. A first suppressor 434
formed similar to the suppressor 406 shown in FIG. 7 is connected
with the other end of the dielectric strip 433. In other words, the
NRD guide S4 is substantially constructed by arranging the first
suppressor 434 at one end of the first dielectric strip 433
provided between the pair of parallel plate conductors 430,
431.
[0247] The first dielectric strip 433 has one end thereof connected
with the millimeter wave signal oscillator 432 via the first
suppressor 434 and the other end thereof connected with a second
suppressor 436 to be described later. Identified by 435 is a
circulator made of two ferrite disks which are ferromagnetic plates
vertically opposed to each other and having first, second and third
connecting portions (none of them is shown) each having one end
thereof connected with a corresponding one of second, third and
fourth suppressors 436, 437, 438 formed similar to the suppressor
406 shown in FIG. 7. In other words, the second suppressor 436 is
connected with the first connecting portion of the circulator 435,
the third suppressor 437 is connected with the second connecting
portion thereof and the fourth suppressor 438 is connected with the
third connecting portion thereof.
[0248] Identified by 439 is a second dielectric strip having one
end thereof connected with the other end of the second suppressor
437. The second dielectric strip 439 is adapted to transmit a
millimeter wave signal and is formed similar to the dielectric
strip 403 shown in FIG. 7. In other words, the NRD guide S4 is
substantially constructed by arranging the second suppressor 437 at
one end of the second dielectric strip 439 provided between the
pair of parallel plate conductors 430, 431. The leading end of the
second dielectric strip 439 is tapered to form a transmitting
antenna 440.
[0249] Identified by 441 is a third dielectric strip having one end
thereof connected with the other end of the fourth suppressor 438.
The third dielectric strip 441 is adapted to transmit a millimeter
wave signal and is formed similar to the dielectric strip 403 shown
in FIG. 7. In other words, the NRD guide S4 is substantially
constructed by arranging the fourth suppressor 438 at one end of
the third dielectric strip 441 provided between the pair of
parallel plate conductors 430, 431. A nonreflective termination 442
for attenuating the millimeter wave signal received by the
transmitting antenna 440 is provided at the leading end of the
third dielectric strip 441.
[0250] Identified by 443 is a fourth dielectric strip for
transmitting part of the millimeter wave signal to a mixer 447 by
arranging one end thereof in vicinity of the first dielectric strip
433 for electromagnetic coupling or joining one end thereof with
the first dielectric strip 433. Identified by 444 is a
nonreflective termination provided at one end of the fourth
dielectric strip 443 opposite from the mixer 447 to be described
later. Identified by 445 is a fifth dielectric strip which is
formed at its leading end with a receiving antenna 446 by, e.g.,
tapering and is adapted to transmit a radio wave received by this
receiving antenna 446 to the mixer 447. The mixer 447 mixes part of
the millimeter wave signal with the received wave to generate an
intermediate-frequency signal by electromagnetically coupling an
intermediate position of the fourth dielectric strip 443 and, that
of the fifth dielectric strip 445 by bringing them closer to each
other or joining them.
[0251] The nonreflective termination 442 (444) is provided with a
resistance film 442a (444a) therein, as shown in FIG. 10B. The
resistance film 442a (444a) is formed along a plane separating the
nonreflective termination 442 (444) into an upper half and a lower
half and parallel with the pair of parallel plate conductors 430,
431. Further, the resistance film may be formed on side surfaces or
end surface of the nonreflective termination 442 (444). The
resistance film 442a (444a) is made of an NiCr alloy or resin
containing conductive particles such as carbon particles. The
nonreflective termination 442 (444) provided with the resistance
film 442a (444a) may be integrally formed with the third dielectric
strip 441 (443) by simultaneous sintering.
[0252] In the construction of FIG. 10A, the fourth dielectric strip
443 may be coupled by arranging one end thereof in vicinity of the
second dielectric strip 439 for electromagnetic coupling or joining
one end thereof with the second dielectric strip 439, so that part
of the millimeter wave signal can be transmitted to the mixer
447.
[0253] The millimeter wave signal oscillators 412, 432 used in the
millimeter wave radar module shown in FIGS. 9 and 10 are shown in
FIGS. 11 and 12. Identified by 452 in FIGS. 11 and 12 is a metallic
member such as a metallic block for mounting a Gunn diode 453. The
Gunn diode 453 is one type of the high-frequency diodes for
oscillating a millimeter wave signal and is mounted on one side
surface of the metallic member 452. Identified by 454 is a circuit
board on which a choke-type bias supply strip 455, functioning as a
low-pass filter, is formed to supply a bias voltage to the Gunn
diode 453 and prevent leak of a high-frequency signal. Identified
by 456 is a strip conductor such as a metallic foil ribbon for
connecting the choke-type bias supply strip 455 and an upper
conductor of the Gunn diode 453.
[0254] Identified by 457 is a metal strip resonator formed by
providing a metal strip 458 for resonance on a dielectric
substrate, and by 459 a dielectric waveguide for leading the
high-frequency signal resonated by the metal strip 457 to the
outside of the millimeter wave signal oscillator. A circuit board
461 carrying a varactor diode 460 which is used for frequency
modulation and is one type of the variable-capacitance diodes is
provided in an intermediate position of the dielectric waveguide
459. A bias voltage applying direction of the varactor diode 460 is
a direction (direction of electric field) perpendicular to the,
transmission direction of the high-frequency signal and parallel to
the principle planes of the parallel plate conductors 430, 431.
Further, the bias voltage applying direction of the varactor diode
460 coincides with a direction of an electric field of a
high-frequency signal of the LSMO, mode transmitting in the
dielectric waveguide 459, so that the bias voltage is controlled to
change an electrostatic capacitance of the varactor diode 460 by
electromagnetically coupling the high-frequency signal and the
varactor diode 460, thereby controlling the frequency of the
high-frequency signal. Identified by 462 is a dielectric plate
having a high relative dielectric constant used for the impedance
matching between the varactor diode 460 and the dielectric
waveguide 459.
[0255] As shown in FIG. 12, the second choke-type bias supply strip
463 having the varactor diode 460 of beam lead type mounted in its
intermediate position is formed on one principle plane of the
circuit board 461. Further, connection electrodes 464, 465 are
formed at portions of the second chock-type bias supply strip 463
connected with the varactor diode 460.
[0256] In this construction, the high-frequency signal oscillated
by the Gunn diode 453 is led to the dielectric waveguide 459 via
the metal strip resonator 457. Subsequently, part of the
high-frequency signal is reflected by the varactor diode 460 to
return to the Gunn diode 453. This reflection signal changes as the
electrostatic capacitance of the varactor diode 460 changes,
thereby changing an oscillating frequency.
[0257] FMCW (frequency modulation continuous waves) system, pulse
system or like system is applicable to the millimeter wave radar
module shown in FIGS. 9 and 10. In the case of the FMCW system, an
operation principle is as follows. An input signal representing a
change of voltage amplitude with time in the form of a triangular
wave, sine wave or other wave is inputted to a MODIN terminal for
modulated signal input of the millimeter wave signal oscillator,
and an output signal thereof is frequency-modulated so that
deviation of an output frequency of the millimeter wave signal
oscillator is represented by a triangular wave, sine wave or other
wave. In the case that the output signal (transmitted wave) is
radiated via the transmitting/receiving antenna 423 or the
transmitting antenna 440, a reflected wave (received wave) returns
with a time lag resulting from a time required for the radio wave
to propagate back and forth if a target is present in front of the
transmitting/receiving antenna 423 or the transmitting antenna 440.
At this time, a frequency difference between the transmitted wave
and the received wave is outputted to an IFOUT terminal at the
output side of the mixer 415 or 447.
[0258] A distance to the target can be calculated in accordance
with following equation by analyzing a frequency component of the
output frequency of the IFOUT terminal or the like:
Fif=4R.multidot.fm.multidot..DELTA.f/c
[0259] (Fif: IF (intermediate frequency) output frequency, R:
distance, fm: modulating frequency, .DELTA.f: frequency deviation
range, c: velocity of light).
[0260] In the millimeter wave signal oscillators 412, 432 of the
millimeter wave radar modules according to the embodiment of the
invention, the choke-type bias supply strip 455 and the strip
conductor 456 are made of, e.g., Cu, Al, Au, Ag, W, Ti, Ni, Cr, Pd,
Pt. Particularly, Cu, Ag are preferable because of a satisfactory
electric conductivity, a small transmission loss and a large
oscillation output.
[0261] The strip conductor 456 is electromagnetically coupled to
the metallic member 452 at a specified spacing from the outer
surface of the metallic member 452 and bridges the choke-type bias
supply strip 455 and the Gunn diode 453. More specifically, one end
of the strip conductor 456 is connected with one end of the
choke-type bias supply strip 455 by, e.g., soldering, the other end
thereof is connected with an upper conductor of the Gunn diode 453
by, e.g., soldering, and an intermediate portion thereof extends in
the air.
[0262] The metallic member 452 is sufficient to be a metallic
conductor since it also acts as an electric ground for the Gunn
diode 453, and the material therefor is not particularly restricted
provided that it is a metallic (including alloys) conductor. The
metallic member 452 may be made of, e.g., brass (Cu--Zn alloy), Al,
Cu, SUS (stainless steel), Ag, Au, Pt. Alternatively, the metallic
member 452 may be a metallic block entirely made of a metal,
ceramics or plastic block having its outer surfaces entirely or
partly coated with metal plating, or an insulating substrate having
its outer surfaces entirely or partly coated with a conductive
resin material.
[0263] The millimeter wave radar module as a millimeter wave
transmitting/receiving apparatus according to the embodiment of the
invention can effectively attenuate electromagnetic waves of
unnecessary modes such as LSE mode and TEM mode and reduce the
transmission loss of the LSM mode. Therefore, in the case that the
millimeter wave transmitting/receiving apparatus is applied to the
millimeter wave radar or the like, a detection distance can be
increased (type of FIG. 9A). Further, this millimeter wave radar
module can effectively attenuate electromagnetic waves of
unnecessary modes such as LSE mode and TEM mode and reduce the
transmission loss of the LSM mode, and the millimeter wave signal
to be transmitted is not introduced to the mixer via the
circulator. Therefore, in the case that the millimeter wave
transmitting/receiving apparatus is applied to the millimeter wave
radar or the like, this can bring about better transmission
characteristics of the millimeter wave signal, reduced noise of the
received signal, and an extended detection distance (type of FIG.
10A).
[0264] Examples of the NRD guide S4 provided with the suppressor is
described below.
EXAMPLE 7
[0265] The suppressor 406 shown in FIG. 7 and 8 was formed as
follows. A mixed powder was prepared by adding 15 weight parts of
SiO2 and 10 weight parts of ZnO to 75 weight parts of glass having
an average particle diameter of 1.5 to 2.5 .mu.m and containing 44
weight percent of SiO.sub.2, 29 weight percent of Al.sub.2O.sub.3,
11 weight percent of MgO, 7 weight percent of ZnO and 9 weight
percent of B.sub.2O.sub.3, and adding ceramics filler having an
average particle diameter of 1.5 to 2.5 .mu.m to the mixture. After
a slurry was prepared by adding and mixing an organic binder and a
solvent to and with the mixed powder, a sheet was formed of the
resulting mixed powder by the doctor blade method.
[0266] A Cu paste was applied to one outer surface of the sheet by
the screen printing method such that four conductive layers having
dimensions: a=1.5 mm, b=0.48 mm, d=0.40 mm and a thickness of 10
.mu.m were formed in such a pattern as shown in FIG. 8. A sheet
formed in a manner similar to the above sheet was placed on the
above sheet. The obtained laminated matter was cut to a height
(thickness) of 1.8 mm and a length of 3.5 mm to form a suppressor
406 after being sintered at 850 to 1000.degree. C. in a nonoxiding
atmosphere.
[0267] Two aluminum plates having a thickness of 6 mm as the
parallel plate conductors 401, 402 are arranged at a spacing of 1.8
mm, and the dielectric strip 403 having a rectangular cross section
of 1.8 mm (height).times.0.8 mm (width) and made of cordierite
ceramics having a relative dielectric constant of 4.8 and the
suppressor 406 connected with an end of the dielectric strip 403
were placed between the aluminum plates.
[0268] An LSE mode attenuation characteristic of the suppressor 406
was estimated. At this time, an NRD guide for converting
electromagnetic waves excited in the LSM mode into those of the LSE
mode or those of the LSM mode, e.g., the one constructed such that
electromagnetic waves of the LSM mode are converted into those of
the LSE mode by connecting a dielectric strip with, an end of an
other dielectric strip transmitting the electromagnetic waves of
the LSM mode at a right angle to the transmission direction, and
the converted electromagnetic waves of the LSE mode are converted
back to those of the LSM mode by connecting a still other
dielectric strip with the other end of the other dielectric strip
at a right angle to the transmission direction was fabricated. The
suppressor 406 was inserted in a portion where the electromagnetic
waves of the LSE mode were transmitted, and a transmission
characteristic at 75 to 85 GHz was measured using a network
analyzer. The measurement result is shown in FIG. 13.
[0269] As is clear from FIG. 13, an attenuation characteristic of
about 30 dB or higher was obtained in a frequency range of about 75
to 80 GHz, and an attenuation characteristic of about 20 dB or
higher was obtained in a frequency range of about 80 to 85 GHz. As
a whole, the attenuation characteristic was at maximum about 50 dB
and at minimum about 20 dB. An excellent characteristic was
obtained in a frequency band wider than an actual operating
frequency band at present of 76 to 77 GHz.
COMPARATIVE EXAMPLE 5
[0270] An NRD guide similar to Example 7 was fabricated except that
a conductive layer of a conventional pattern shown in FIG. 37 was
formed. The formed pattern was: L=0.5 mm, w1=1.5 mm, w2=0.2 mm,
thickness=10 .mu.m in FIG. 37. A result of a measurement conducted
as in Example 7 is shown in FIG. 14.
[0271] As is clear from FIG. 14, an attenuation characteristic of
about 24 to 40 dB was obtained in a frequency range of about 75 to
76 GHz, an attenuation characteristic of about 13 to 28 dB was
obtained in a frequency range of about 76 to 83 GHz, and an
attenuation characteristic of about 15 to 36 dB was obtained in a
frequency range of about 83 to 85 GHz. As a whole, the attenuation
characteristic was at maximum about 40 dB and at minimum about 13
dB.
[0272] Example 7 had better attenuation characteristic than
Comparative Example 5 over a wide range.
[0273] Since the parallel plate conductors are formed so that the
arithmetic average roughness Ra of their inner surfaces satisfies
0.1 .mu.m.ltoreq.Ra.ltoreq.50 .mu.m as described above, the NRD
guide S4 according to the fourth embodiment of the invention has an
excellent durability and can effectively suppress the transmission
loss of high-frequency signals because the dielectric strip is
strongly secured to the inner surfaces of the parallel plate
conductors.
[0274] Further, since the suppressor formed by a plurality of
conductive layers provided at specified intervals substantially in
a widthwise middle position of the dielectric strip in a plane
perpendicular to the principle planes of the parallel plate
conductors and parallel to the transmission direction of the
high-frequency signal is formed at the end of the dielectric strip
in the NRD guide S4, electromagnetic waves of unnecessary modes do
not resonate. As a result, electromagnetic waves of the LSE mode
which is an unnecessary mode can be effectively attenuated. Since
the conductive layers are thinner as compared with conductive pins,
reflection by the conductive layers of the LSM mode which is a
transmission mode are unlikely to occur, with the result that the
transmission loss thereof can be reduced.
[0275] Preferably, a dimension of each conductive layer in the
transmission direction is half the wavelength of the TEM
electromagnetic waves of the high-frequency signal and the
thickness thereof is 0.1 mm or smaller. With such conductive
layers, the electromagnetic waves of the LSE mode which is an
unnecessary mode can be effectively attenuated, and the
transmission loss by the conductive layers of the LSM mode can be
significantly reduced.
[0276] Further, in the millimeter wave transmitting/receiving
apparatus to which the NRD guide S4 is applied, the electromagnetic
waves of the LSE mode which is an unnecessary mode can be
effectively attenuated and the transmission loss of the
electromagnetic waves of the LSM mode which is a transmission mode
can be reduced by providing the suppressor similar to the above at
the end of the dielectric strip. The millimeter wave signal to be
transmitted is introduced to the mixer via the circulator to a
smaller degree. As a result, if the millimeter wave
transmitting/receiving apparatus is applied to a millimeter wave
radar or the like, this can bring about better transmission
characteristics of the millimeter wave signal, reduced noise of the
received signal, and an extended detection distance.
[0277] In the millimeter wave transmitting/receiving apparatus to
which the NRD guide S4 is applied and in which the transmitting
antenna and the receiving antenna are independently provided, the
electromagnetic waves of the LSE mode which is an unnecessary mode
can be effectively attenuated and the transmission loss of the
electromagnetic waves of the LSM mode which is a transmission mode
can be reduced by providing the suppressor similar to the above at
the end of the dielectric strip. Further, the millimeter wave
signal received by the transmitting antenna is not introduced to
the millimeter wave signal oscillator. Therefore, if the millimeter
wave transmitting/receiving apparatus is applied to a millimeter
wave radar module or the like, this can bring about better
transmission characteristics of the millimeter wave signal, reduced
oscillation noise, and an extended detection distance.
[0278] FIGS. 15 and 16 show an NRD guide according to a fifth
embodiment of the invention. FIG. 15 is a perspective view showing
an essential portion of the internal construction of the NRD guide
and FIG. 16 is a side view thereof. An NRD guide S5 according to
the fifth embodiment is mainly designed to solve the problems in
the prior art.
[0279] In FIGS. 15 and 16, the NRD guide S5 is comprised of a pair
of parallel plate conductors 501, 502 vertically opposed to each
other at a spacing which is equal to or shorter than half the
wavelength of a high-frequency signal to be transmitted, two
ferrite disks 503, 504 which are ferromagnetic plates vertically
opposed to each other to construct a circulator between the pair of
parallel plate conductors 501, 502, three dielectric strips 505,
506, 507 which are waveguide strips radially arranged around the
ferrite disks 503, 504 at intervals of 120.degree. C., and three
dielectric strips 508, 509, 510 which are suppressor strips for
constructing suppressors to block electromagnetic waves of the LSE
mode and arranged between the ferrite disks 503, 504 and the
dielectric strips 505, 506, 507. It should be noted that the
wavelength here is a wavelength in the air (free space) at an
operating frequency.
[0280] The respective parallel plate conductors 501, 502 are formed
of conductive plates made of, e.g., Cu, Al, Fe, Ag, Au, Pt,. SUS
(Stainless Steel), brass (Cu--Zn alloy) since they need to have a
high electric conductivity and an excellent processability.
Alternatively, they may be formed of insulating plates made of
ceramics, resin or like material having a conductive layer made of
the above metallic materials formed on its outer surface. Further,
the surfaces (inner surfaces) of the parallel plate conductors 501,
502 facing the dielectric strips 505 to 507, 508 to 510 are ground
so that an arithmetic average roughness Ra thereof satisfies 0.1
.mu.m.ltoreq.Ra.ltoreq.50 .mu.m.
[0281] This arithmetic average roughness Ra is the same as the one
defined in the first embodiment, and the range thereof is set as
above for the same reason mentioned in the first embodiment. The
arithmetic average roughness Ra satisfies preferably 0.3
.mu.m.ltoreq.Ra.ltoreq.25 .mu.m, and more preferably 0.4
.mu.m.ltoreq.Ra.ltoreq.10 .mu.m.
[0282] The ferrite disks 503, 504 have an identical shape and are
concentrically opposed to each other with their principle planes
held in contact with the inner surfaces of the parallel plate
conductors 501, 502. Depending on cases, they may be spaced apart
from the inner surfaces of the parallel plate conductors 501, 502
by a specified distance. In this embodiment, the principle planes
of the two ferrite disks 503, 504 are in flush with those of the
suppressors 518 to 520, realizing a construction preferable in
reducing a transmission loss of a high-frequency signal.
[0283] The thickness of the ferrite disks 503, 504 are preferably
0.15 to 0.03 mm if a ferrite having a relative dielectric constant
of 13 is used in a band of 77 GHz used for an automotive millimeter
wave radar. If the thickness is below 0.15 mm, it is difficult to
handle the ferrite disks 503, 504 due to their reduced strength. If
the thickness exceeds 0.03 mm, the diameter of the ferrite disks
503, 504 needs to be decreased in order to prevent a shift of a
pass band. A decreased diameter leads to a deteriorated isolation
of the circulator.
[0284] The diameter of the ferrite disks 503, 504 is preferably 1
to 3 mm. The isolation of the circulator is deteriorated if the
diameter is below 1 mm, whereas the thickness of the ferrite disks
503, 504 needs to be below 0.15 mm in order to prevent a shift of a
pass band, making it difficult to handle the ferrite disks 503,
504, if the diameter exceeds 3 mm.
[0285] Right polygonal ferrite plates may be used instead of the
ferrite disks 503, 504. In this case, if the number of the
dielectric strips to be connected is n (n is an integer of 2 or
larger), the plan shape of the ferrite plates is a right polygon
having m sides (m is an integer of 3 or larger, and m=n+1). The
ferrite disks 503, 504 function as a circulator by providing a
magnet, an electromagnet or the like for applying a d.c. (direct
current) magnetic field of about 355500 A/m to the principle planes
of the ferrite disks 503, 504 from the outside of the parallel
plate conductors 501, 502.
[0286] The dielectric strips 505 to 507 as waveguide strips may be
made of a resin dielectric material such as Teflon, polystyrene or
glass epoxy or a cordierite (2MgO.2Al.sub.2O.sub.3.5SiO.sub.2)
ceramics, alumina (Al.sub.2O.sub.3) ceramics, glass ceramics or
forsterite (2MgO.SiO.sub.2) ceramics or like ceramics having a
lower relative dielectric constant. This is because these materials
can suppress a transmission loss in a high-frequency band.
Particularly in view of a dielectric characteristic,
processability, strength, miniaturization, reliability, etc., the
dielectric strips 505 to 507 are desirably made of cordierite
ceramics.
[0287] The dielectric strips 508 to 510 as suppressor strips
forming suppressors are made of, for example, the same material as
the dielectric strips 505 to 507 and are arranged continuously with
one ends of the dielectric strips 505 to 507. Further, impedance
matching members 512, 513, 514 are provided on the end faces of the
dielectric strips 508 to 510. The dielectric strips 508 to 510 may
be spaced apart from the one ends of the dielectric strips 505 to
507 by a specified distance. Strip conductors 515, 516, 517 made of
copper foils or the like are formed inside, particularly at the
centers of the dielectric strips 508 to 510.
[0288] These strip conductors 515, 516, 517 are arranged in a plane
perpendicular to the principle planes of the parallel plate
conductors 501, 502 and parallel to the transmission direction of
the high-frequency signal, and adapted to block electromagnetic
waves of the LSE mode whose electric field propagates in a
direction (longitudinal direction in FIGS. 15, 16) perpendicular to
the principle planes of the parallel plate conductors 501, 502. A
.lambda./4 choke pattern is applied to the strip conductors 515,
516, 517 in order to remove the TEM mode. Suppressors for an NRD
guide 518, 519, 520 are formed by the corresponding dielectric
strips 508 to 510 and strip conductors 515, 516, 517.
[0289] In the NRD guide S5 thus constructed, an electromagnetic
wave having transmitted along the dielectric strip 505 are
transmitted to the dielectric strip 506 after its wavefront is
rotated counterclockwise, but not transmitted to the dielectric
strip 507. Likewise, an electromagnetic wave having transmitted
along the dielectric strip 506 is transmitted to the dielectric
strip 507. In this way, transmission paths of the electromagnetic
waves are changed. It should be appreciated that the rotating
direction of the wavefront of the high-frequency signal is reversed
if S-pole and N-pole of the d.c. (direct current) magnetic field
applied substantially perpendicularly to the principle planes of
the ferrite disks 503, 504 are reversed.
[0290] Although three dielectric strips 505 to 507 are arranged
such that the directions of transmission paths are spaced at even
intervals of 1200 in the NRD guide S5, two dielectric strips may be
arranged while being spaced apart by 120.degree.. In such a case,
the high-frequency signal has its transmission path changed only in
one direction. The above NRD guide S5 can convert the transmission
path of the high-frequency signal in three directions: from the
dielectric strip 505 to the dielectric strip 506, from the
dielectric strip 506 to the dielectric strip 507 and from
dielectric strip 507 to the dielectric strip 505. Alternatively,
four dielectric strips may be arranged while being spaced apart at
even intervals of 90.degree. or six dielectric strips may be
arranged while being spaced apart at even intervals of
60.degree..
[0291] The impedance matching members 512 to 514 have a relative
dielectric constant different from that of the dielectric strips
505 to 510 and preferably satisfies
-10.ltoreq..epsilon.r2-.epsilon.r1.ltoreq.20
(.epsilon.r2.noteq..epsilon.r1) if .epsilon.r1, .epsilon.r2 denote
the relative dielectric constant of the dielectric strips 505 to
510 and that of the impedance matching members 512 to 514,
respectively. If .epsilon.r2-.epsilon.r1<-10, it is difficult to
handle the impedance matching members 512 to 514 because the width
of the transmission paths thereof is reduced. Thus, positioning
precision thereof is reduced and the transmission loss is likely to
vary from product to product. If 20<.epsilon.r2-.epsilon.r1, the
dimension of the impedance matching members 512 to 514 in the
transmission direction needs to be shortened for impedance
matching, making it difficult to handle them and reducing their
geometric precision. As a result, the transmission loss is likely
to vary from product to product if .epsilon.r2=.epsilon.r1, it is
difficult to match impedances since reflection of the
high-frequency signal is large as shown in FIG. 22.
[0292] The thickness of the impedance matching members 512 to 514
in the transmission direction is preferably 0.05 to 0.5 mm. If the
thickness is below 0.05 mm, it is difficult to handle them and
their geometric precision is reduced, making the transmission loss
likely to vary from product to product. If the thickness exceeds
0.5 mm, an isolation characteristic is deteriorated.
[0293] The impedance matching members 512 to 514 are preferably
made of an aluminaceramics having a relatively high relative
dielectric constant of about 9.7, a forsterite (2MgO.SiO.sub.2)
ceramics having a relative dielectric constant of 7, a spinel
(MgO.Al.sub.2O.sub.3) ceramics having a relative dielectric
constant of about 8, a mullite (3Al.sub.2O.sub.3.2SiO.sub.2), a
silicon nitride (Si.sub.3N.sub.4) ceramics, or like ceramics. This
is because these materials have a small dielectric loss and an
excellent strength.
[0294] The impedance matching members 512 to 514 define stepped
portions 585 to 587 in positions corresponding to the upper and
lower surfaces of the dielectric strips 508 to 510 (or suppressors
518 to 520). A spacing between the upper and lower stepped portions
585 to 587 is set substantially equal to a spacing between the two
ferrite disks 503, 504. The impedance matching members 512 to 514
are connected with the two ferrite disks 503, 504 by arranging the
ferrite disks 503, 504 to hold the impedance matching members 512
to 514 at the stepped portions 585 to 587. In this case, the two
ferrite disks 503, 504 can be highly concentrically held by the
impedance matching members 512, 514 and it is not necessary to
provide a positioning member such as a dielectric spacer between
them. However, the connecting construction of the ferrite disks
503, 504 and the impedance matching members 512 to 514 is not
limited to the above. In FIGS. 15 and 16 the impedance matching
members 512 to 514 are in the form of a flat plate, thereby
defining two step portions 585 (586, 587) for each of the
dielectric strips 508 to 510. However, it may be appreciated to
provide an impedance matching member in the form of a plate having
two step portions at upper and lower sides or at right and left
sides, thereby defining four step portions for each of the
dielectric strips 508 to 510, specifically two step portions
between the end face of the dielectric strip 508 (509, 510) and the
impedance matching member, and another step portions which are
formed in the impedance matching member.
[0295] The high-frequency band in the present invention corresponds
to a microwave band and a millimeter wave band ranging from in the
order of 10 GHz to in the order to 100 GHz, and the NRD guide S5
according to the fifth embodiment is suitably used in a
high-frequency band, for example, above 30 GHz, particularly above
50 GHz, and further above 70 GHz.
[0296] The NRD guide S5 according to the fifth embodiment is used
in a wireless LAN or a millimeter wave radar installed in an
automotive vehicle with a high-frequency diode such as a Gunn diode
incorporated thereinto as a high frequency generating device. In
such a millimeter wave radar, a millimeter wave is projected to an
obstacle and other automotive vehicles present around an automotive
vehicle in which this radar is installed, the reflected wave is
combined with the original millimeter wave to obtain a beat signal
(intermediate-frequency signal), and distances to the obstacle and
other automotive vehicles and their moving speeds are measured by
analyzing this beat signal.
[0297] Since the electromagnetic waves are converged and, thus,
difficult to diffuse or radiate by arranging the impedance matching
members 512 to 514 at the end faces of the suppressors 518 to 520
in the NRD guide S5 according to the fifth embodiment, an insertion
loss and an isolation characteristic of a high-frequency signal are
further improved in a high-frequency band, and a band range is
significantly extended.
[0298] In the case that the dielectric strips 505 to 507 of the NRD
guide S5 are made of, e.g., ceramics, each of them may be comprised
of a plurality of strip sections as in the first embodiment shown
in FIG. 1 and the end faces of the respective strip sections may be
opposed to each other at a spacing equal to or shorter than
.lambda./8 (.lambda. is a wavelength of a high-frequency signal to
be transmitted). This can reduce conversion of electromagnetic
waves of the LSM mode into those of the LSE mode and enables an
easy fabrication of a dielectric strip having even a complicated
shape formed by linear and curved portions. In other words, if the
dielectric strips 505 to 507 are each formed by a plurality of
strip sections, the bend loss can be reduced even if the dielectric
strips 505 to 507 include curved portions.
[0299] Next, a millimeter wave radar module as a millimeter wave
transmitting/receiving apparatus to which the NRD guide S5 is
applied is described. FIGS. 17 to 20 show millimeter wave radar
modules according to the embodiment of the invention, wherein FIG.
17A is a plan view of a millimeter wave radar module having an
integrated transmitting/receiving antenna, FIG. 18A is a plan view
of a millimeter wave radar module having independent transmitting
antenna and receiving antenna, FIG. 19 is a perspective view
showing a millimeter wave signal oscillator, and FIG. 20 is a
perspective view of a circuit board on which a variable-capacitance
diode (varactor diode) for the millimeter wave signal oscillator is
provided.
[0300] Identified by 520, 521 in FIG. 17A are a pair of vertically
arranged parallel plate conductors which are constructed similar to
the parallel plate conductors 501, 502 shown in FIG. 16. Various
devices to be described later are inserted between the pair of
parallel plate conductors 520, 521. It should be noted that the
upper parallel plate conductor 521 is partly cut away in order to
make an entire construction visible.
[0301] Identified by 522 is a circulator made of two ferrite disks
which are ferromagnetic plates vertically opposed to each other and
having first, second and third connecting portions (none of them is
shown) each having one end thereof connected with a corresponding
one of first, second and third suppressors 523, 525 formed similar
to the suppressors 518 to 520 shown in FIG. 15. In other words, the
first suppressor 523 is connected with the first connecting portion
of the circulator 522, the second suppressor 524 is connected with
the second connecting portion thereof and the third suppressor 525
is connected with the third connecting portion thereof.
[0302] An impedance matching member 526 is provided at a side of
the first suppressor 523 toward the circulator 522; an impedance
matching member 527 is provided at a side of the second suppressor
524 toward the circulator 522; and an impedance matching member 528
is provided at a side of the third suppressor 525 toward the
circulator 522. The impedance matching members 526 to 528 are
formed similar to the impedance matching members 512 to 514 shown
in FIG. 15.
[0303] Identified by 529 is a first dielectric strip having one end
thereof connected with the other end of the first suppressor 523.
The first dielectric strip 529 is adapted to transmit a millimeter
wave signal and is formed similar to the dielectric strips 505 to
507 shown in FIG. 15. Identified by 530 is a millimeter wave
oscillator which is provided at the other end of the first
dielectric strip 529. The millimeter wave signal oscillator 530
outputs a frequency-modulated millimeter wave signal to be
transmitted by cyclically controlling the bias voltage of a
variable-capacitance diode disposed in vicinity of a high-frequency
diode (high-frequency generating device) to have a triangular wave,
a sine wave or other wave such that a bias voltage applying
direction coincides with a direction of an electric field of a
high-frequency signal.
[0304] Identified by 531 is a second dielectric strip having one
end thereof connected with the other end of the second suppressor
524. The second dielectric strip 531 is adapted to transmit a
millimeter wave signal and is formed similar to the dielectric
strips 505 to 507 shown in FIG. 15. The leading end of the second
dielectric strip 531 is tapered to form a transmitting/receiving
antenna 532.
[0305] Identified by 533 is a third dielectric strip having one end
thereof connected with the other end of the third suppressor 525.
The third dielectric strip 533 is formed similar to the dielectric
strips 505 to 507 shown in FIG. 15. The third dielectric strip 533
transmits a radio wave received by the transmitting/receiving
antenna 532 and outputted from the third connecting portion of the
circulator 522 via the second dielectric strip 531 to a mixer 536
to be described later.
[0306] Identified by 534 is a fourth dielectric strip for
transmitting part of the millimeter wave signal to the mixer 536 by
being coupled to the first dielectric strip 529 in such a manner
that one end thereof is arranged in vicinity of the first
dielectric strip 529 for electromagnetic coupling or one end
thereof is joined with the first dielectric strip 529. Identified
by 535 is a nonreflective termination (terminator) provided at one
end of the fourth dielectric strip 534 opposite from the mixer 536.
The mixer 536 mixes part of the millimeter wave signal with the
received wave to generate an intermediate-frequency signal by
electromagnetically coupling or joining an intermediate position of
the third dielectric strip 533 and that of the fourth dielectric
strip 534.
[0307] The nonreflective termination 535 is provided with a
resistance film 535a therein, as shown in FIG. 17B. The resistance
film 535a is formed along a plane separating the nonreflective
termination 535 into an upper half and a lower half and parallel
with the pair of parallel plate conductors 520, 521. Further, the
resistance film 535a may be formed on side surfaces or end surface
of the nonreflective termination 535. The resistance film 535a is
made of an NiCr alloy or resin containing conductive particles such
as carbon particles. The nonreflective termination 535 provided
with the resistance film 535a may be integrally formed with the
fourth dielectric strip 534 by simultaneous sintering.
[0308] As is clear from the above description, the NRD guide S5 is
substantially constructed by arranging the circulator 522, the
first to third suppressors 523, 524, 525, and the first to third
dielectric strips 529, 531, 533 between the pair of parallel plate
conductors 520, 521.
[0309] In the construction of FIG. 17A, a frequency control can be
executed by providing a switch constructed similar to the one shown
in FIG. 20 in an intermediate position of the first dielectric
strip 529. A switch shown in FIG. 20 is constructed such that a
second choke-type bias supply strip 573 is formed on one principle
plane of a circuit board 571 and a PIN diode or Schottky barrier
diode of beam lead type is mounted in an intermediate position of
the strip 573 by soldering.
[0310] Another embodiment of the millimeter wave radar module as an
inventive millimeter wave transmitting/receiving apparatus to which
the NRD guide S5 is applied is of the type shown in FIG. 18A having
independent transmitting antenna and receiving antenna. Identified
by 540, 541 in FIG. 18A are a pair of vertically arranged parallel
plate conductors which are constructed similar to the parallel
plate conductors 501, 502 shown in FIG. 16. It should be noted that
the upper parallel plate conductor 541 is partly cut away in order
to make an entire construction visible.
[0311] Identified by 542 is a circulator made of two ferrite disks
which are ferromagnetic plates vertically opposed to each other and
having first, second and third connecting portions (none of them is
shown) each having one end thereof connected with a corresponding
one of first, second and third suppressors 543, 545 formed similar
to the suppressors 518 to 520 shown in FIG. 15. In other words, the
first suppressor 543 is connected with the first connecting portion
of the circulator 542, the second suppressor 544 is connected with
the second connecting portion thereof and the third suppressor 545
is connected with the third connecting portion thereof.
[0312] An impedance matching member 546 is provided at a side of
the first suppressor 543 toward the circulator 542; an impedance
matching member 547 is provided at a side of the second suppressor
544 toward the circulator 542; and an impedance matching member 548
is provided at a side of the third suppressor 545 toward the
circulator 542. The impedance matching members 546 to 548 are
formed similar to the impedance matching members 512 to 514 shown
in FIG. 15.
[0313] Identified by 549 is a first dielectric strip having one end
thereof connected with the other end of the first suppressor 543.
The first dielectric strip 549 is adapted to transmit a millimeter
wave signal and is formed similar to the dielectric strips 505 to
507 shown in FIG. 15. Identified by 550 is a millimeter wave
oscillator which is provided at the other end of the first
dielectric strip 549. The millimeter wave signal oscillator 550
outputs a frequency-modulated millimeter wave signal to be
transmitted by cyclically controlling a bias voltage of a
variable-capacitance diode disposed in vicinity of a high-frequency
diode (high-frequency generating device) to have a triangular wave,
a sine wave or other wave such that a bias voltage applying
direction coincides with a direction of an electric field of a
high-frequency signal.
[0314] Identified by 551 is a second dielectric strip having one
end thereof connected with the other end of the second suppressor
544. The second dielectric strip 551 is adapted to transmit a
millimeter wave signal and is formed similar to the dielectric
strips 505 to 507 shown in FIG. 15. The leading end of the second
dielectric strip 551 is tapered to form a transmitting antenna
552.
[0315] Identified by 553 is a third dielectric strip having one end
thereof connected with the other end of the third suppressor 545.
The third dielectric strip 553 is adapted to transmit a millimeter
wave signal and is formed similar to the dielectric strips 505 to
507 shown in FIG. 15. At the leading end of the third dielectric
strip 553 is provided a nonreflective termination 554 for
attenuating a millimeter wave signal to be transmitted.
[0316] As is clear from the above description, the NRD guide S5 is
substantially constructed by arranging the circulator 542, the
first to third suppressors 543, 544, 545, and the first to third
dielectric strips 549, 551, 553 between the pair of parallel plate
conductors 540, 541.
[0317] Identified by 556 is a fourth dielectric strip for
transmitting part of the millimeter wave signal to a mixer 560 to
be described later by being coupled to the first dielectric strip
549 in such a manner that one end thereof is arranged in vicinity
of the first dielectric strip 549 for electromagnetic coupling or
one end thereof is joined with the first dielectric strip 549.
Identified by 557 is a nonreflective termination provided at one
end of the fourth dielectric strip 556 opposite from the mixer 560.
Identified by 558 is a fifth dielectric strip formed at its leading
end with a receiving antenna 559 by, e.g., tapering. The fifth
dielectric strip 558 transmits a radio wave received by the
receiving antenna 559 to the mixer 560. The mixer 560 mixes part of
the millimeter wave signal with the received wave to generate an
intermediate-frequency signal by electromagnetically coupling or
joining an intermediate position of the fourth dielectric strip 556
and that of the fifth dielectric strip 558.
[0318] The nonreflective termination 554 (557) is provided with a
resistance film 554a (557a) therein, as shown in FIG. 18B. The
resistance film 554a (557a) is formed along a plane separating the
nonreflective termination 554 (557) into an upper half and a lower
half and parallel with the pair of parallel plate conductors 540,
541. Further, the resistance film 554a (557a) may be formed on side
surfaces or end surface of the nonreflective termination 554 (557).
The resistance film 554a (557a) is made of an NiCr alloy or resin
containing conductive particles such as carbon particles. The
nonreflective termination 554 (557) provided with the resistance
film 554a (557a) may be integrally formed with the third dielectric
strip 553 (556) by simultaneous sintering.
[0319] In the construction of FIG. 18A, a frequency control can be
executed by providing a switch constructed similar to the one shown
in FIG. 20 in an intermediate position of the first dielectric
strip 549. The switch shown in FIG. 20 is constructed such that the
second choke-type bias supply strip 573 is formed on one principle
plane of the circuit board 571 and a PIN diode or Schottky barrier
diode of beam lead type is mounted in an intermediate position of
the strip 573 by soldering.
[0320] The construction of the millimeter wave signal oscillators
530, 550 used in the millimeter wave radar module shown in FIGS. 17
and 18 are shown in FIGS. 19 and 20. Identified by 562 in FIGS. 19
and 20 is a metallic member such as a metallic block for mounting a
Gunn diode 563. The Gunn diode 563 is one type of the
high-frequency diodes for oscillating a millimeter wave signal and
is mounted on one side surface of the metallic member 562.
Identified by 564 is a circuit board on which the choke-type bias
supply strip 565, which functions as a low-pass filter, is formed
to supply a bias voltage to the Gunn diode 563 and prevent leak of
a high-frequency signal. Identified by 566 is a strip conductor
such as a metallic foil ribbon for connecting the choke-type bias
supply strip 565 and an upper conductor of the Gunn diode 563.
[0321] Identified by 567 is a metal strip resonator formed by
providing a metal strip 568 for resonance on a dielectric
substrate, and by 569 a dielectric waveguide for leading the
high-frequency signal resonated by the metal strip 567 to the
outside of the millimeter wave signal oscillator. A circuit board
571 carrying a varactor diode 570 which is used for frequency
modulation and is one type of the variable-capacitance diodes is
provided in an intermediate position of the dielectric waveguide
569. A bias voltage applying direction of the varactor diode 570 is
a direction (direction of electric field) perpendicular to the
transmission direction of the high-frequency signal and parallel to
the principle planes of the parallel plate conductors 520, 521,
540, 541. Further, the bias voltage applying direction of the
varactor diode 570 coincides with a direction of an electric field
of a high-frequency signal of the LSMOL mode transmitting in the
dielectric waveguide 569, so that the bias voltage is controlled to
change an electrostatic capacitance of the varactor diode 570 by
electromagnetically coupling the high-frequency signal and the
varactor diode 570, thereby controlling the frequency of the
high-frequency signal. Identified by 572 is a dielectric plate
having a high relative dielectric constant used for the impedance
matching between the varactor diode 570 and the dielectric
waveguide 569.
[0322] As shown in FIG. 20, a second choke-type bias supply strip
573 having the varactor diode 570 of beam lead type mounted in its
intermediate position is formed on one principle plane of the
circuit board 571. Further, connection electrodes 574, 575 are
formed at portions of the second chock-type bias supply strip 573
connected with the varactor diode 570.
[0323] In this construction, the high-frequency signal oscillated
by the Gunn diode 563 is led to the dielectric waveguide 569 via
the metal strip resonator 567. Subsequently, part of the
high-frequency signal is reflected by the varactor diode 570 to
return to the Gunn diode 563. This reflection signal changes as the
electrostatic capacitance of the varactor diode 570 changes,
thereby changing an oscillating frequency.
[0324] The millimeter wave radar modules shown in FIGS. 17 and 18
adopt the FMCW (frequency modulation continuous waves) system,
whose operation principle is as follows. An input signal
representing a change of voltage amplitude with time in the form of
a triangular wave, sine wave or other wave is inputted to a MODIN
terminal for modulated signal input of the millimeter wave signal
oscillator, and an output signal thereof is frequency-modulated so
that deviation of an output frequency of the millimeter wave signal
oscillator is represented by a triangular wave, sine wave or other
wave. In the case that the output signal (transmitted wave) is
radiated via the transmitting/receiving antenna 532 or the
transmitting antenna 552, a reflected wave (received wave) returns
with a time lag resulting from a time required for the radio to
propagate back and forth if a target is present in front of the
transmitting/receiving antenna 532 or the transmitting antenna 552.
At this time, a frequency difference between the transmitted wave
and the received wave is outputted to an IFOUT terminal at the
output side of the mixer 536 or 560.
[0325] A distance to the target can be calculated in accordance
with following equation by analyzing a frequency component of the
output frequency of the IFOUT terminal or the like:
Fif=4R.multidot.fm.multidot..DELTA.f/c
[0326] (Fif: IF output frequency, R: distance, fm: modulating
frequency, .DELTA.f: frequency deviation range, c: velocity of
light).
[0327] In the millimeter wave signal oscillators 530, 550 of the
millimeter wave radar modules according to the embodiment of the
invention, the choke-type bias supply strip 565 and the strip
conductor 566 are made of, e.g., Cu, Al, Au, Ag, W, Ti, Ni, Cr, Pd,
Pt. Particularly, Cu, Ag are preferable because of a satisfactory
electric conductivity, a small transmission loss and a large
oscillation output.
[0328] The strip conductor 566 is electromagnetically coupled to
the metallic member 562 at a specified spacing from the outer
surface of the metallic member 562 and bridges the choke-type bias
supply strip 565 and the Gunn diode 563. More specifically, one end
of the strip conductor 566 is connected with one end of the
choke-type bias supply strip 565 by, e.g., soldering, the other end
thereof is connected with an upper conductor of the Gunn diode 563
by, e.g., soldering, and an intermediate portion thereof extends in
the air.
[0329] The metallic member 562 is sufficient to be a metallic
conductor since it also acts as an electric ground for the Gunn
diode 563, and the material therefor is not particularly restricted
provided that it is a metallic (including alloys) conductor. The
metallic member 562 may be made of, e.g., brass (Cu--Zn alloy), Al,
Cu, SUS (stainless steel), Ag, Au, Pt. Alternatively, the metallic
member 562 may be a metallic block entirely made of a metal,
ceramics or plastic block having its outer surfaces entirely or
partly coated with metal plating, or an insulating substrate having
its outer surfaces entirely or partly coated with a conductive
resin material.
[0330] The millimeter wave radar module as a millimeter wave
transmitting/receiving apparatus according to the embodiment of the
invention has further improved transmission loss and isolation
characteristic of a millimeter wave signal in a high-frequency band
having a wider range. As a result, in the case that this millimeter
wave transmitting/receiving apparatus is applied to a millimeter
wave radar, a detection distance can be increased (type of FIG.
17A). Further, the transmission loss and isolation characteristic
of a high-frequency signal are further improved in a high-frequency
band having a wider range, and the millimeter wave signal to be
transmitted is not introduced to the mixer via the circulator. As a
result, noise of the received signal is reduced and a detection
distance is increased. Thus, the detection distance of the
millimeter wave radar can be further increased (type of FIG.
18A).
[0331] Examples of the inventive NRD guide S5 provided with the
circulator are described below.
EXAMPLE 8
[0332] The NRD guide S5 provided with the circulator shown in FIGS.
15 and 16 was constructed as follows. Two aluminum plates having a
thickness of 6 mm as parallel plate conductors were arranged at a
spacing of 1.8 mm, and three dielectric strips 505 to 507 having a
rectangular cross section of 1.8 mm (height).times.0.8 mm (width)
and made of cordierite ceramics having a relative dielectric
constant of 4.8 were radially arranged at even intervals of
120.degree. such that the suppressors 518 to 520 at the leading
ends of the dielectric strips 505 to 507 were connected with two
ferrite disks 503, 504. It should be noted that the suppressors 518
to 520 were formed by providing the strip conductors 515 to 517
made of a copper foil and having a .lambda./4 choke pattern inside
the suppressors 518 to 520.
[0333] At this time, the dielectric strips 505 to 507 were arranged
such that upper and lower surfaces of the suppressors 518 to 520
were in flush with the principle planes of the two ferrite disks
503, 504. More specifically, the two ferrite disks 503, 504 were
arranged to face the inner surfaces of the respective parallel
plate conductors; the stepped portions 585 to 587 were so formed at
the upper and lower ends of the impedance matching members 512 to
514 as to correspond to the upper and lower surfaces of the
suppressors 518 to 520 (stepped portions 585 to 587 have a height
corresponding to the thickness of the ferrite disks 503, 504); the
impedance matching members 512 to 514 were held between the two
ferrite disks 503, 504 by engaging the two ferrite disks 503, 504
with the stepped portions 585 to 587. Further, the upper and lower
principle planes of the ferrite disks 503, 504 and those of the
dielectric strips 505 to 507 were held in contact with the inner
surfaces of the parallel plate conductors.
[0334] The ferrite disks 503, 504 had a diameter of 2.0 mm and a
thickness of 0.25 mm, and magnets were provided above and below the
ferrite disks 503, 504 for applying a d.c. (direct current)
magnetic field of about 355500 A/m. Specifically, a round recess
having a diameter of 12.5 mm and a depth of 5 mm was formed in a
position of each parallel plate conductor corresponding to the
ferrite disk 503, 504 outside concentrically with the ferrite disk
503, 504, and a magnet having a diameter of 12.5 mm and a thickness
of 5 mm was placed in each recess. Further, the impedance matching
members 512 to 514 were made of an aluminaceramics having a
relative dielectric constant of 9.7, a cross section thereof along
a plane perpendicular to a transmission direction had a height of
1.3 mm and a width of 0.8 mm, and a dimension (thickness) thereof
in the transmission direction was 0.1 mm. Therefore, the height of
the stepped portions 585 to 587 was 0.25 mm.
[0335] A transmission characteristic .vertline.S21.vertline. and an
isolation characteristic .vertline.S31.vertline. of a
high-frequency signal in the NRD guide S5 thus constructed were
measured in a high-frequency band of 75 to 80 GHz using a spectrum
analyzer. The measurement result is shown in FIG. 21. Further, a
conventional NRD guide shown in FIG. 39 was fabricated as in
Example 7 except that the stepped portions 732 to 734 were formed
by cutting off the upper and lower ends of the leading end of the
suppressors 724 to 726, and a transmission characteristic
.vertline.S21.vertline. and an isolation characteristic
.vertline.S31.vertline. thereof were similarly measured. The
measurement result is shown in FIG. 22.
[0336] As is clear from FIGS. 21 and 22, the transmission
characteristic .vertline.S21.vertline. in FIG. 21 shows a small
loss of about -1 to -1.5 dB over the entire band and the isolation
characteristic .vertline.S31.vertline. in FIG. 21 is satisfactory
over a wide range while being at highest about -35 dB and at lowest
about -25 dB in the NRD guide S5. On the other hand, the
transmission characteristic .vertline.S21.vertline. in FIG. 22 is
about -2 to -2.5 dB over the entire band and the isolation
characteristic .vertline.S31.vertline. in FIG. 22 is at highest
about -20 dB and at lowest about -19 dB: i.e., both characteristics
were poor in the comparative example shown in FIG. 22.
[0337] Since the parallel plate conductors are formed so that the
arithmetic average roughness Ra of their inner surfaces satisfies
0.1 .mu.m.ltoreq.Ra.ltoreq.50 .mu.m as described above, the NRD
guide S5 according to the fifth embodiment of the invention has an
excellent durability and can effectively suppress the transmission
loss of high-frequency signals because the dielectric strip is
strongly secured to the inner surfaces of the parallel plate
conductors.
[0338] Further, in the NRD guide S5, the two ferrite plates are
opposed to inner surfaces of the parallel plate conductors, and a
plurality of dielectric strips for transmitting a high-frequency
signal which are substantially radially arranged around the two
ferrite plates are connected with the suppressors provided at the
leading ends of the respective dielectric strips for blocking
electromagnetic waves of the LSE mode via the impedance matching
members having a relative dielectric constant different from that
of the dielectric strips and provided at the leading ends of the
suppressors. Accordingly, the electromagnetic waves are converged
by the impedance matching members having a relative dielectric
constant larger than that of the dielectric strip and become
difficult to reflect. Thus, the insertion loss and isolation loss
of the high-frequency signal in a high-frequency band having a
wider range can be further improved. Further, since it is not
necessary to control the width of the dielectric waveguide in order
to reduce a transmission loss, and the transmission characteristic
can be improved by the impedance matching members, the NRD guide S5
can be easily fabricated with an excellent operability and suitable
for mass production.
[0339] Preferably, the stepped portions having a height
substantially equal to the thickness of the two ferrite plates are
formed at the upper and lower ends of the impedance matching
members, and the two ferrite plates are connected with the
impedance matching members at the stepped portions while holding
the impedance matching members therebetween. Then, it is not
necessary to provide a dielectric spacer or the like for holding
the ferrite plates, the suppressors and the ferrite plates can be
positioned with an improved precision. Thus, the circulator can be
assembled with an improved repeatability, making it difficult for
the two ferrite plates to become eccentric with respect to each
other. As a result, a stable circulator characteristic can be
repeatedly obtained. Further, the NRD guide S5 can be easily
fabricated and suitable for mass production.
[0340] The millimeter wave radar module as an inventive millimeter
wave transmitting/receiving apparatus can have improved
transmission loss and isolation characteristic of a high-frequency
signal in a high-frequency band having a wider range by applying
the construction of the NRD guide S5 thereto, with the result that
a detection distance can be increased in the case of application to
a millimeter wave radar or the like. Further, the millimeter wave
radar module having independent transmitting and receiving antennas
as an inventive millimeter wave transmitting/receiving apparatus
can have improved transmission loss and isolation characteristic of
a high-frequency signal in a high-frequency band having a wider
range and eliminate a possibility of introducing the millimeter
wave signal to be transmitted into the mixer via the circulator by
applying the construction of the NRD guide S5 thereto. Accordingly,
in the case of application to a millimeter wave radar, noise of the
received signal is reduced and a detection distance is increased.
This results in an excellent transmission characteristic of a
millimeter wave signal, which further increases a detection
distance.
[0341] FIG. 23 is a perspective view showing an NRD guide according
to a sixth embodiment of the invention. An NRD guide S6 according
to the sixth embodiment is mainly designed to solve the problems in
the prior art. In FIG. 23, the NRD guide S6 is constructed by
arranging a dielectric strip 603 having a rectangular cross section
of a.times.b between a pair of parallel plate conductors 601, 602
vertically opposed to each other at a spacing which is equal to or
shorter than half the wavelength of a high-frequency signal to be
transmitted, and connecting a metallic waveguide 604 with the
dielectric strip 603. An open termination 605 is formed at one end
of the dielectric strip 603. In the NRD guide thus constructed,
electric fields of standing waves of the LSM mode as shown in FIG.
24 are created. It should be noted that the wavelength here is a
wavelength in the air (free space) at an operating frequency.
[0342] The respective parallel plate conductors 601, 602 are formed
of conductive plates made of, e.g., Cu, Al, Fe, Ag, Au, Pt, SUS
(Stainless Steel), brass (Cu--Zn alloy) since they need to have a
high electric conductivity and an excellent processability.
Alternatively, they may be formed of insulating plates made of
ceramics, resin or like material having a conductive layer made of
the above metallic materials formed on its outer surface. Further,
the surfaces (inner surfaces) of the parallel plate conductors 601,
602 facing the dielectric strip 603 are ground so that an
arithmetic average roughness Ra thereof satisfies 0.1
.mu.m.ltoreq.Ra.ltoreq.50 .mu.m.
[0343] This arithmetic average roughness Ra is the same as the one
defined in the first embodiment, and the range thereof is set as
above for the same reason mentioned in the first embodiment. The
arithmetic average roughness Ra satisfies preferably 0.3
.mu.m.ltoreq.Ra.ltoreq.25 .mu.m, and more preferably 0.4
.mu.m.ltoreq.Ra.ltoreq.10 .mu.m.
[0344] The upper parallel plate conductor 602 is formed with an
opening 606 in a position corresponding to any position where the
electric fields of standing waves are strong, i.e., E1, E2, E3, E4
of FIG. 24 in order to connect the dielectric strip 603 and the
metallic waveguide 604. Position E1 is located near the open
termination 605 of the dielectric strip 603, whereas positions
E2(m=1), E3(m=2), E4(m=3) are located in positions corresponding to
distances, which are m/2 (m is a positive integer) of a guide
wavelength, from the open termination 605. The opening 606 where
the dielectric strip 603 and the metallic waveguide 604 are
connected is preferably formed in position E2, E3 or E4 in view of
a transmission loss, and more preferably in position E2 in view of
a transmission loss and miniaturization.
[0345] The dielectric strip 603 and the metallic waveguide 604 of
the NRD guide S6 are connected via the opening 606 formed in the
parallel plate conductor 602, such that directions of these
electric fields coincide. Specifically, as shown in FIG. 23, an
open termination 607 at one end of the metallic waveguide 604 is
connected via the opening 606 such that a direction (L-direction)
of longer sides of the quadrilateral (rectangular) cross section of
the metallic waveguide 604 is parallel to a transmission direction
of a high-frequency signal in the dielectric strip 603. Another
connecting construction is, as in an NRD guide S6a shown in FIG.
25, such that a metallic waveguide 604 having a closed termination
608 at one end and an open termination 609 at the other end is
used, an opening 610 is formed in a position spaced from an end
face of the closed termination 608 by n/2+1/4 (n is zero or a
positive integer) of a guide wavelength of the metallic waveguide
604, and the metallic waveguide 604 and the dielectric strip 603
are connected such that the opening 606 of the parallel plate
conductor 602 and an opening 610 formed in the metallic waveguide
604 are substantially in agreement. It should be noted that the
openings 606, 610 have substantially the same shape.
[0346] In the construction of FIG. 25, the opening 610 of the
metallic waveguide 604 is preferably formed such that its center is
spaced by three fourths of the guide wavelength of the metallic
waveguide 604 from the end face of the termination 608 of the
metallic waveguide 604. In this case, a connection loss can be
minimized and electromagnetic waves propagate in the metallic
waveguide 604 only in a direction toward the open termination 609
to thereby minimize a transmission loss by connecting the metallic
waveguide 604.in a position close to its closed termination 608
where the intensity of the electric field is at maximum. It should
be noted that the electromagnetic field is likely to disturb in the
position spaced from the end face of the closed termination 608 by
a fourth of the guide wavelength of the metallic waveguide 604, and
is stable in the position spaced from the end face of the closed
termination 608 by three fourths of the guide wavelength of the
metallic waveguide 604.
[0347] The opening 606 formed in the parallel plate conductor 602
is preferably in the form of a quadrilateral such as a rectangle
having a length (L) equal to or shorter than half the guide
wavelength of the dielectric strip 603 and a width (W)
substantially same as that of the dielectric strip 603 as shown in
FIG. 23. The opening 606 having such a rectangular shape has a
small connection loss and a satisfactory processability. Instead of
being quadrilateral, the opening 606 may be circular or oblong.
[0348] Further, as in an NRD guide S6b shown in FIG. 26, the
dielectric strip 603 is preferably formed wider in an area
extending from a portion corresponding to the opening 606 of the
parallel plate conductor 602 to the open termination 605 than the
other portion. In this case, a guide wavelength is shortened in the
widened portion of the dielectric strip 603, with the result that a
portion where the intensity of the electric field is at maximum is
shifted in such a direction as to shorten the dielectric strip 603,
enabling miniaturization of the dielectric strip 603. Denoted at x,
x1 are the width of the widened portion and that of the narrow
portion of the dielectric strip 603, respectively. It is preferable
to satisfy 1.ltoreq.x/x1.ltoreq.2. If x/x1<1, the guide
wavelength of the dielectric strip 603 is elongated, leading to a
larger size of the NRD guide. If 2<x/x1, reflection of the
high-frequency signal or the like is likely to occur at the portion
where the width of the dielectric strip 603 is changed, thereby
increasing the transmission loss.
[0349] Even if the area extending from the portion corresponding to
the opening 606 to the open termination 605 is formed of a
dielectric having a larger dielectric constant instead of forming
the widened portion of the dielectric strip 603 as above, the same
effects can be obtained.
[0350] Further, as shown in FIG. 25, a horn antenna 611 having a
gradually widening opening may be preferably formed at the open
termination 609 at the other end of the metallic waveguide 604. By
taking such a construction, the open termination 609 of the
metallic waveguide 604 can be used also as antenna. As compared to
a case where another antenna member is provided, the connection
loss by a connecting portion with the antenna member is smaller.
Further, this construction can be applied to a millimeter wave
radar system installed in an automotive vehicle or the like having
a high-efficiency transmission characteristic by enabling
transmission and reception of a high-frequency signal to and from
the outside.
[0351] Further, as shown in FIG. 27, it is preferable to provide an
antenna member 614 such as a flat antenna at an open termination
613 at the other end of the metallic waveguide 604. In this case,
the connection loss of the antenna member 614 is slightly larger
than the case of FIG. 25. However, transmission and reception of a
high-frequency signal to and from the outside are enabled by
providing the antenna member at an open termination 613, and this
construction can be applied to a millimeter wave radar system
installed in an automotive vehicle or the like having a
high-efficiency transmission characteristic.
[0352] In this embodiment, open antennas which can be provided at
the metallic waveguide 604 include a horn antenna and a laminated
type open antenna, and flat antennas include a patch antenna, a
slot antenna, a print dipole antenna. Particularly, flat antennas
are preferable in view of miniaturization of a millimeter wave
integrated circuit in a millimeter wave band. Various other
antennas can be used for this purpose provided that they belong to
the above category.
[0353] The metallic waveguide 604 may be made of Cu, Al, Fe, Ag,
Au, Pt, SUS (Stainless Steel), brass (Cu--Zn alloy) or like
conductive material or formed of a conductive material obtained by
forming a conductive layer of the above metallic material on the
outer surface of an insulating material made of ceramics, a resin
or the like. These conducive materials are preferable in view of a
high electric conductivity and an excellent processability.
[0354] The dielectric strip 503 is preferably made of a resin
dielectric material such as Teflon, polystyrene or ceramic such as
a cordierite (2MgO.2Al.sub.2O.sub.3.5SiO.sub.2) ceramics, alumina
(Al.sub.2O.sub.3) ceramics, glass ceramics. This is because these
materials can suppress the transmission loss in a high-frequency
band.
[0355] The high-frequency band in this embodiment corresponds to a
microwave band and a millimeter wave band ranging from in the order
of 10 GHz to in the order to 100 GHz, for example, above 30 GHz,
particularly above 50 GHz, and further above 70 GHz.
[0356] The NRD guide S6 according to the sixth embodiment is used
in a wireless LAN or a millimeter wave radar installed in an
automotive vehicle with a high-frequency diode such as a Gunn diode
incorporated thereinto as a high frequency generating device. For
example, a millimeter wave is projected to an obstacle and other
automotive vehicles present around an automotive vehicle in which
this radar is installed, the reflected wave is combined with the
original millimeter wave to obtain a beat signal
(intermediate-frequency signal), and distances to the obstacle and
other automotive vehicles and their moving speeds are measured by
analyzing this beat signal.
[0357] According to the sixth embodiment, the dielectric strip and
the metallic waveguide can be connected with a small connection
loss, and the NRD guide and the millimeter wave integrated circuit
or the like into which the NRD guide is incorporated can be
miniaturized.
[0358] In the case that the dielectric strip 603 of the NRD guide
S6 is made of, e.g., ceramics, it may be comprised of a plurality
of strip sections as in the first embodiment shown in FIG. 1 and
the end faces of the respective strip sections may be opposed to
each other at a spacing equal to or shorter than .lambda./8
(.lambda. is a wavelength of a high-frequency signal to be
transmitted). This can reduce conversion of electromagnetic waves
of the LSM mode into those of the LSE mode and enables an easy
fabrication of a dielectric strip having even a complicated shape
formed by linear and curved portions. In other words, if the
dielectric strip 603 is formed by a plurality of strip sections, a
bend loss can be reduced even if the dielectric strip 603 includes
a curved portion.
[0359] Next, a millimeter wave radar module as a millimeter wave
transmitting/receiving apparatus to which the NRD guide S6 is
applied is described. FIGS. 28 to 31 show millimeter wave radar
modules according to the embodiment of the invention, wherein FIG.
28A is a plan view of a millimeter wave radar module having an
integrated transmitting/receiving antenna, FIG. 29A is a plan view
of a millimeter wave radar module having independent transmitting
antenna and receiving antenna, FIG. 30 is a perspective view
showing a millimeter wave signal oscillator, and FIG. 31 is a
perspective view of a circuit board on which a variable-capacitance
diode (varactor diode) for the millimeter wave signal oscillator is
provided.
[0360] Identified by 620, 621 in FIG. 28A are a pair of vertically
arranged parallel plate conductors which are constructed similar to
the parallel plate conductors 601, 602 shown in FIG. 23. It should
be noted that the upper parallel plate conductor 621 is partly cut
away in order to make an entire construction visible.
[0361] Identified by 622 is a circulator made of two ferrite disks
which are ferromagnetic plates vertically opposed to each other
while being held in contact with the inner surfaces of the parallel
plate conductors 601, 602 and having first, second and third
connecting portions (none of them is shown).
[0362] Identified by 623 is a first dielectric strip having one end
thereof connected with the first connecting portion of the
circulator 622. The first dielectric strip 623 is adapted to
transmit a millimeter wave signal and is formed similar to the
dielectric strip 603 shown in FIG. 23. Identified by 624 is a
millimeter wave oscillator which is provided at the other end of
the first dielectric strip 623. The millimeter wave signal
oscillator 624 outputs a frequency-modulated millimeter wave signal
to be transmitted by cyclically controlling a bias voltage of a
variable-capacitance diode disposed in vicinity of a high-frequency
diode (high-frequency generating device) to have a triangular wave,
a sine wave or other wave such that a bias voltage applying
direction coincides with a direction of an electric field of a
high-frequency signal.
[0363] Identified by 625 is a second dielectric strip having one
end thereof connected with the second connecting portion of the
circulator 622. The second dielectric strip 625 is adapted to
transmit a millimeter wave signal and is formed similar to the
dielectric strip 603 shown in FIG. 23. The second dielectric strip
625 has a transmitting/receiving antenna 626 at its leading end.
This transmitting/receiving antenna 626 is to be connected with an
open termination of a metallic: waveguide similar to the metallic
waveguide 604 shown in FIG. 23 as described later.
[0364] Identified by 627 is a third dielectric strip having one end
thereof connected with the third connecting portion of the
circulator 622. The third dielectric strip 627 is formed similar to
the dielectric strip 603 shown in FIG. 23. The third dielectric
strip 627 transmits a radio wave received by the
transmitting/receiving antenna 626 and outputted from the third
connecting portion of the circulator 622 via the second dielectric
strip 625 to a mixer 630 to be described later.
[0365] Identified by 628 is a fourth dielectric strip for
transmitting part of the millimeter wave signal to the mixer 630 by
being coupled to the first dielectric strip 623 in such a manner
that one end thereof is arranged in vicinity of the first
dielectric strip 623 for electromagnetic coupling or one end
thereof is joined with the first dielectric strip 623. Identified
by 629 is a nonreflective termination (terminator) provided at one
end of the fourth dielectric strip 628 opposite from the mixer 630.
The mixer 630 mixes part of the millimeter wave signal with the
received wave to generate an intermediate-frequency signal by
electromagnetically coupling or joining an intermediate position of
the third dielectric strip 627 and that of the fourth dielectric
strip 628. It may be appreciated to provide a suppressor between
the circulator 622 and each of the dielectric strips 623, 625, and
627.
[0366] The nonreflective termination 629 is provided with a
resistance film 629a therein, as shown in FIG. 28B. The resistance
film 629a is formed along a plane separating the nonreflective
termination 629 into an upper half and a lower half and parallel
with the pair of parallel plate conductors 620, 621. Further, the
resistance film 629a may be formed on side surfaces or end surface
of the nonreflective termination 629. The resistance film 629a is
made of an NiCr alloy or resin containing conductive particles such
as carbon particles. The nonreflective termination 629 provided
with the resistance film 629a may be integrally formed with the
fourth dielectric strip 628 by simultaneous sintering.
[0367] The above various parts are arranged between the parallel
plate conductors 620, 621 spaced apart by a distance equal to or
shorter than half the wavelength of the millimeter wave signal. At
least one of the parallel plate conductors 620, 621 is formed with
an opening in a position corresponding to a position where the
electric field of a standing wave of the LSM mode is at maximum.
The open termination at the other end of the metallic waveguide
formed similar to the metallic waveguide 604 shown in FIG. 23 and
having the transmitting/receiving antenna 626 provided at one end
thereof is connected with this opening. The constructions of the
metallic waveguide and the transmitting/receiving antenna and the
connecting construction of the metallic waveguide and the
transmitting/receiving antenna are similar to those described
above. In other words, the NRD guide S6 is substantially
constructed by arranging the second dielectric strip 625 and the
transmitting/receiving antenna 626 between the pair of parallel
plate conductors 620, 621.
[0368] In the construction of FIG. 28A, a frequency control can be
executed by providing a switch constructed similar to the one shown
in FIG. 31 in an intermediate position of the first dielectric
strip 623. A switch shown in FIG. 31 is constructed such that a
choke-type bias supply strip 673 is formed on one principle plane
of a circuit board 671 and a PIN diode or Schottky barrier diode of
beam lead type is mounted in an intermediate position of the strip
673 by soldering.
[0369] Another embodiment of the millimeter wave radar module as an
inventive millimeter wave transmitting/receiving apparatus to which
the NRD guide S6 is applied is of the type shown in FIG. 29A having
independent transmitting antenna and receiving antenna. Identified
by 640, 641 in FIG. 29A are a pair of vertically arranged parallel
plate conductors which are constructed similar to the parallel
plate conductors 601, 602 shown in FIG. 23. It should be noted that
the upper parallel plate conductor 641 is partly cut away in order
to make an entire construction visible.
[0370] Identified by 642 is a circulator made of two ferrite disks
which are ferromagnetic plates vertically opposed to each other and
having first, second and third connecting portions (none of them is
shown).
[0371] Identified by 643 is a first dielectric strip having one end
thereof connected with the first connecting portion of the
circulator 642. The first dielectric strip 643 is adapted to
transmit a millimeter wave signal and is formed similar to the
dielectric strip 603 shown in FIG. 23. Identified by 644 is a
millimeter wave oscillator which is provided at the other end of
the first dielectric strip 643. The millimeter wave signal
oscillator 644 outputs a frequency-modulated millimeter wave signal
to be transmitted by cyclically controlling a bias voltage of a
variable-capacitance diode disposed in vicinity of a high-frequency
diode (high-frequency generating device) to have a triangular wave,
a sine wave or other wave such that a bias voltage applying
direction coincides with a direction of an electric field of a
high-frequency signal.
[0372] Identified by 645 is a second dielectric strip having one
end thereof connected with the second connecting portion of the
circulator 642. The second dielectric strip 645 is adapted to
transmit a millimeter wave signal and is formed similar to the
dielectric strip 603 shown in FIG. 23. The second dielectric strip
645 has a transmitting/receiving antenna 646 at its leading end.
This transmitting/receiving antenna 646 is to be connected with an
open termination of a metallic waveguide similar to the metallic
waveguide 604 shown in FIG. 23 as described later.
[0373] Identified by 647 is a third dielectric strip having one end
thereof connected with the third connecting portion of the
circulator 642. The third dielectric strip 647 is formed similar to
the dielectric strip 603 shown in FIG. 23. The third dielectric
strip 647 transmits a radio wave received by the
transmitting/receiving antenna 646 is provided at its leading end
with a nonreflective termination 648 for attenuating a millimeter
wave signal to be transmitted.
[0374] Identified by 650 is a fourth dielectric strip for
transmitting part of the millimeter wave signal to the mixer 654 by
being coupled to the first dielectric strip 643 in such a manner
that one end thereof is arranged in vicinity of the first
dielectric strip 643 for electromagnetic coupling or one end
thereof is joined with the first dielectric strip 643. Identified
by 651 is a nonreflective termination provided at one end of the
fourth, dielectric strip 650 opposite from the mixer 654.
Identified by 652 is a fifth dielectric strip formed at its leading
end with a receiving antenna 653. The fifth dielectric strip 652
transmits a radio wave received by the receiving antenna 653 to the
mixer 654. The receiving antenna 653 is to be connected with an
open termination of a metallic waveguide similar to the metallic
waveguide 604 shown in FIG. 23 as described later.
[0375] The nonreflective termination 648 (651) is provided with a
resistance film 648a (651a) therein, as shown in FIG. 29B. The
resistance film 648a (651a) is formed along a plane separating the
nonreflective termination 648 (651) into an upper half and a lower
half and parallel with the pair of parallel plate conductors 640,
641. Further, the resistance film 648a (651a) may be formed on side
surfaces or end surface of the nonreflective termination 648 (651).
The resistance film 648a (651a) is made of an NiCr alloy or resin
containing conductive particles such as carbon particles. The
nonreflective termination 648 (651) provided with the resistance
film 648a (651a) may be integrally formed with the third dielectric
strip 647 (650) by simultaneous sintering.
[0376] The mixer 654 mixes part of the millimeter wave signal with
the received wave to generate an intermediate-frequency signal by
electromagnetically coupling or joining an intermediate position of
the fourth dielectric strip 650 and that of the fifth dielectric
strip 652. It may be appreciated to provide a suppressor between
the circulator 642 and each of the dielectric strips 643, 645, and
647.
[0377] The above various parts are arranged between the parallel
plate conductors 640, 641 spaced apart by a distance equal to or
shorter than half the wavelength of the millimeter wave signal. At
least one of the parallel plate conductors 640, 641 is formed with
openings in positions corresponding to a position where the
electric field of a standing wave of the LSM mode transmitting in
the second dielectric strip 645 is at maximum and a position where
the electric field of a standing wave of the LSM mode transmitting
in the fifth dielectric strip 652 is at maximum. The open
termination at the other end of the metallic waveguide formed
similar to the metallic waveguide 604 shown in FIG. 23 and having
the transmitting antenna 646 or the receiving antenna 653 provided
at one end thereof is connected with these openings. The
constructions of the metallic waveguide and the transmitting and
receiving antennas and the connecting construction of the metallic
waveguide and the second and fifth dielectric strips are similar to
those described above. In other words, the NRD guide S6 is
substantially constructed by arranging the second and fifth
dielectric strips 645, 652 and the transmitting and receiving
antennas 646, 653 between the pair of parallel plate conductors
640, 641.
[0378] In the construction of FIG. 29A, the transmitting antenna
646 may be connected with the leading end of the first dielectric
strip 643 by deleting the circulator 642. In this case, part of the
received wave is likely to enter the millimeter wave signal
oscillator, thereby causing a noise although the construction can
be made smaller. Thus, the construction of FIG. 29A is more
preferable. In the construction of FIG. 29A, a frequency control
can be executed by providing a switch constructed similar to the
one shown in FIG. 31 in an intermediate position of the first
dielectric strip 643. The switch shown in FIG. 31 is constructed
such that the second choke-type bias supply strip 673 is formed on
one principle plane of the circuit board 671 and a PIN diode or
Schottky barrier diode of beam lead type is mounted in an
intermediate position of the strip 673 by soldering.
[0379] The construction of the millimeter wave signal oscillators
624, 644 used in the-millimeter wave radar module shown in FIGS. 28
and 29 are shown in FIGS. 30 and 31. Identified by 662 in FIGS. 19
and 20 is a metallic member such as a metallic block for mounting a
Gunn diode 663. The Gunn diode 663 is one type of the
high-frequency diodes for oscillating a millimeter wave signal and
is mounted on one side surface of the metallic member 662.
Identified by 664 is a circuit board on which the choke-type bias
supply strip 665, which functions as a low-pass filter is formed to
supply a bias voltage to the Gunn diode 663 and prevent leak of a
high-frequency signal. Identified by 666 is a strip conductor such
as a metallic foil ribbon for connecting the choke-type bias supply
strip 665 and an upper conductor of the Gunn diode 663.
[0380] Identified by 667 is a metal strip resonator formed by
providing a metal strip 668 for resonance on a dielectric
substrate, and by 669 a dielectric waveguide for leading the
high-frequency signal resonated by the metal strip 667 to the
outside of the millimeter wave signal oscillator. The circuit board
671 carrying a varactor diode 670 which is used for frequency
modulation and is one type of the variable-capacitance diodes is
provided in an intermediate position of the dielectric waveguide
669. A bias voltage applying direction of the varactor diode 670 is
a direction (direction of electric field) perpendicular to the
transmission direction of the high-frequency signal and parallel to
the principle planes of the parallel plate conductors 620, 621,
640, 641. Further, the bias voltage applying direction of the
varactor diode 670 coincides with a direction of an electric field
of a high-frequency signal of the LSMO.sub.1 mode transmitting in
the dielectric waveguide 669, so that the bias voltage is
controlled to change an electrostatic capacitance of the varactor
diode 670 by electromagnetically coupling the high-frequency signal
and the varactor diode 670, thereby controlling the frequency of
the high-frequency signal. Identified by 672 is a dielectric plate
having a high relative dielectric constant used for the impedance
matching between the varactor diode 670 and the dielectric
waveguide 669.
[0381] As shown in FIG. 31, the second choke-type bias supply strip
673 having the varactor diode 670 of beam lead type mounted in its
intermediate position is formed on one principle plane of the
circuit board 671. Further, connection electrodes 674, 675 are
formed at portions of the second chock-type bias supply strip 673
connected with the varactor diode 670.
[0382] In this construction, the high-frequency signal oscillated
by the Gunn diode 663 is led to the dielectric waveguide 669 via
the metal strip resonator 667. Subsequently, part of the
high-frequency signal is reflected by the varactor diode 670 to
return to the Gunn diode 663. This reflection signal changes as the
electrostatic capacitance of the varactor diode 670 changes,
thereby changing an oscillating frequency.
[0383] The millimeter wave radar modules shown in FIGS. 28 and 29
adopt the FMCW (frequency modulation continuous waves) system,
whose operation principle is as follows. An input signal
representing a change of voltage amplitude with time in the form of
a triangular wave, sine wave or other wave is inputted to a MODIN
terminal for modulated signal input of the millimeter wave signal
oscillator, and an output signal thereof is frequency-modulated so
that deviation of an output frequency of the millimeter wave signal
oscillator is represented by a triangular wave, sine wave or other
wave. In the case that the output signal (transmitted wave) is
radiated via the transmitting/receiving antenna 626 or the
transmitting antenna 646, a reflected wave (received wave) returns
with a time lag resulting from a time required for the radio wave
to propagate back and forth if a target is present in front of the
transmitting/receiving antenna 626 or the transmitting antenna 646.
At this time, a frequency difference between the transmitted wave
and the received wave is outputted to an IFOUT terminal at the
output side of the mixer 630 or 654.
[0384] A distance to the target can be calculated in accordance
with following equation by analyzing a frequency component of the
output frequency of the IFOUT terminal or the like:
Fif=4R.multidot.fm.multidot..DELTA.f/c
[0385] (Fif: IF output frequency, R: distance, fm: modulating
frequency, .DELTA.f: frequency deviation range, c: velocity of
light).
[0386] In the millimeter wave signal oscillators 624, 644 of the
millimeter wave radar modules according to the embodiment of the
invention, the choke-type bias supply strip 665 and the strip
conductor 666 are made of, e.g., Cu, Al, Au, Ag, W, Ti, Ni, Cr, Pd,
Pt. Particularly, Cu, Ag are preferable because of a satisfactory
electric conductivity, a small transmission loss and a large
oscillation output.
[0387] The strip conductor 666 is electromagnetically coupled to
the metallic member 662 at a specified spacing from the outer
surface of the metallic member 662 and bridges the choke-type bias
supply strip 665 and the Gunn diode 663. More specifically, one end
of the strip conductor 666 is connected with one end of the
choke-type bias supply strip 665 by, e.g., soldering, the other end
thereof is connected with an upper conductor of the Gunn diode 663
by, e.g., soldering, and an intermediate portion thereof extends in
the air.
[0388] The metallic member 662 is sufficient to be a metallic
conductor since it also acts as an electric ground for the Gunn
diode 663, and the material therefor is not particularly restricted
provided that it is a metallic (including alloys) conductor. The
metallic member 662 may be made of, e.g., brass (Cu--Zn alloy), Al,
Cu, SUS (stainless steel), Ag, Au, Pt. Alternatively, the metallic
member 662 may be a metallic block entirely made of a metal,
ceramics or plastic block having its outer surfaces entirely or
partly coated with metal plating, or an insulating substrate having
its outer surfaces entirely or partly coated with a conductive
resin material.
[0389] The millimeter wave radar module as a millimeter wave
transmitting/receiving apparatus according to the embodiment of the
invention has an improved transmission, and can increase a
detection distance when being applied to a millimeter wave radar
(type of FIG. 28A). Further, the millimeter wave signal to be
transmitted is not introduced to the mixer via the circulator. As a
result, noise of the received signal is reduced and a detection
distance is increased. Thus, the detection distance of the
millimeter wave radar can be further increased (type of FIG.
29A).
[0390] Examples of the inventive NRD guide S6 provided with a
circulator are described below.
EXAMPLE 9
[0391] The NRD guide S6 provided with a metallic waveguide shown in
FIG. 23 was constructed as follows. Two aluminum plates having a
thickness of 6 mm as parallel plate conductors 601, 602 were
arranged at a spacing of 1.8 mm, and the dielectric strip 603
having a rectangular cross section of 1.8 mm (height).times.0.8 mm
(width) and made of cordierite ceramics having a relative
dielectric constant of 4.8 was arranged between the aluminum
plates, thereby fabricating a main body of the NRD guide S6. The
rectangular opening 606 having a width (w) of 1.27 mm and a length
(L) of 2.54 mm and having a center located in a position distanced
from the open termination 605 of the dielectric strip 603 by 2.5 mm
was formed in one of the aluminum plates.
[0392] Subsequently, the metallic waveguide 604 having the same
cross section as the shape of the opening 606 and made of a
gold-plated brass was connected with the opening 606. A conversion
loss (connection loss; S21) from the LSE mode to the TE mode was
measured for this connecting construction using a network analyzer.
At this time, the connection loss S21 was also measured for an NRD
guide in which the open termination 605 of the dielectric strip 603
was gradually widened toward the end, the widened portion was
caused to project out from the parallel plate conductors 601, 602
to spatially couple and transmit a high-frequency signal to the
metallic waveguide having a rectangular horn and provided outside.
The measurement result is shown in FIG. 32. As is clear from a
graph of FIG. 32, it was found out that a satisfactory conversion
characteristic having a transmission characteristic of about -2 dB
or higher at about 75 to 80 GHz was exhibited, and Example 9
enables a connection with low connection loss and insertion
loss.
EXAMPLE 10
[0393] The open termination 605 of the dielectric strip 603 was
widened as shown in FIG. 26. Assuming that x=1.0 mm, y=3.2 mm, the
rectangular opening 606 having a width (w) of 1.27 mm and a length
(L) of 2.54 mm and having a center located in a position distanced
from the open termination 605 by 1.9 mm in the longitudinal
direction (transmission direction of a high-frequency signal) of
the dielectric strip 603 was formed in the parallel plate conductor
602.
[0394] A conversion characteristic was estimated as in Example 9,
and the estimation result is shown in FIG. 33. As shown in FIG. 33,
it was found out that a satisfactory conversion characteristic
having a transmission characteristic of about -2 dB or higher at
about 75 to 80 GHz was exhibited, a connection with low connection
loss and insertion loss was possible, and the NRD guide S6 can be
made smaller by shortening the dielectric strip 603.
[0395] Since the parallel plate conductors are formed so that the
arithmetic average roughness Ra of their inner surfaces satisfies
0.1 .mu.m.ltoreq.Ra.ltoreq.50 .mu.m as described above, the NRD
guides S6, S6a, S6b according to the sixth embodiment of the
invention have an excellent durability and can effectively suppress
the transmission loss of high-frequency signals because the
dielectric strip is strongly secured to the inner surfaces of the
parallel plate conductors.
[0396] Further, in the NRD guide S6, at least one of the parallel
plate conductors is formed with the opening in a position
corresponding where the electric field of the standing wave of the
LSM mode transmitting in the dielectric strip is at maximum, and
the open termination at one end of the metallic waveguide is
connected with this opening. Accordingly, the dielectric strip and
the metallic waveguide can be connected with a small connection
loss, and the NRD guide and a millimeter wave integrated circuit or
the like into which the NRD guide is incorporated can be
miniaturized.
[0397] Further, in the NRD guide S6a, at least one of the parallel
plate conductors formed with the opening in a position
corresponding to where the electric field of the standing wave of
the LSM mode transmitting in the dielectric strip is at maximum,
and the metallic waveguide having the closed termination at one end
and the open termination at the other end and formed with an
opening in a position which is distanced from the closed
termination by n/2+1/4 (n is zero or a positive integer) of a guide
wavelength are so connected as to join the opening of the parallel
plate conductor with that of the metallic waveguide. Thus, the
metallic waveguide can be firmly arranged by improving its
connection strength, and the entire NRD guide can be thinned so as
to be used in a narrow space by being vertically placed. Further, a
connection loss can be minimized, and electromagnetic waves
propagate only in a direction toward the open termination in the
metallic waveguide, resulting in a minimized transmission loss.
[0398] Further, in the NRD guide S6b, the dielectric strip is
widened in an area extending from the portion corresponding to the
opening of the parallel plate conductor to the open termination
than the other portion. Accordingly, the NRD guide S6b can be made
smaller by shortening the dielectric strip, and the guide
wavelength is shortened at the widened portion of the dielectric
strip, with the result that a portion where the intensity of the
electric field is at maximum is shifted in such a direction as to
shorten the dielectric strip 603, enabling miniaturization of the
dielectric strip 603.
[0399] Further preferably, transmission and reception of a
high-frequency signal as a radio wave are enabled by providing the
open antenna or flat antenna at the open termination at the other
end of the metallic waveguide. Thus, the NRD guide can be applied
to a millimeter wave radar system installed in an automotive
vehicle or the like having a high-efficiency transmission
characteristic. In the case of forming the open termination into a
horn antenna whose opening gradually widens, the open termination
at the other end of the metallic waveguide can be also used as an
antenna, and a connection loss by a connecting portion with the
antenna member is smaller as compared to a case where another
antenna member is provided.
[0400] The millimeter wave radar module as an inventive millimeter
wave transmitting/receiving apparatus can have an improved
transmission loss by applying the construction of the NRD guide S6
thereto, with the result that a detection distance of the
millimeter wave radar can be increased. Further, the millimeter
wave radar module having independent transmitting and receiving
antennas according to the embodiment of the invention has no
possibility that a millimeter wave signal to be transmitted should
be introduced to the mixer via the circulator. Accordingly, noise
of the received signal is reduced and a detection distance is
increased. This results in an excellent transmission characteristic
of a millimeter wave signal, which further increases a detection
distance.
[0401] As described above, an inventive NRD guide comprises the
pair of parallel plate conductors opposed to each other at a
spacing equal to or shorter than half the wavelength of the
high-frequency signal to be transmitted and having opposing inner
surfaces whose arithmetic average roughness Ra satisfies 0.1
.mu.m.ltoreq.Ra.ltoreq.50 .mu.m, and the dielectric strip arranged
between the pair of parallel plate conductors while being held in
contact with the respective inner surfaces of the parallel plate
conductors.
[0402] In the NRD guide, since the inner surfaces have a suitable
unevenness, the dielectric strip is strongly secured to the inner
surfaces by the anchor effect to exhibit an excellent durability.
Further, current paths on the inner surfaces can be shortened to
reduce a surface resistance, with the result that the transmission
loss of the high-frequency signal can be effectively
suppressed.
[0403] Preferably, the dielectric strip may include a plurality of
strip unit sections and formed by connecting the plurality of strip
unit sections one after another such that end faces thereof are
opposed to each other at a spacing equal to or shorter than 1/8 of
the wavelength of the high-frequency signal.
[0404] By successively connecting the plurality of strip unit
members (strip sections) at specified intervals, a dielectric strip
having a complicated shape can be easily formed by linear and
curved portions. Further, the dielectric strip is unlikely to be
influenced by a stress created from a difference in thermal
expansion between the parallel plate conductors and the dielectric
strip resulting from an atmospheric temperature change and a stress
created by an external impact. Thus, an NRD guide which has a
higher degree of freedom and a smaller size and is inexpensive can
be constructed.
[0405] Preferably, the dielectric strip may be made of ceramics
containing a multiple oxide of Mg, Al, Si as a main component and
having a Q-value of 1000 or larger in a frequency range of 50 to 90
GHz.
[0406] Since the dielectric strip made of ceramics having a
relative dielectric constant lower than a conventionally used
aluminaceramics or like material is used, conversion of the
electromagnetic waves of the LSM mode into those of the LSE mode
can be reduced to suppress a loss of the high-frequency signal.
Thus, using the ceramics containing a multiple oxide of Mg, Al, Si
as a main component, a dielectric strip which has a smaller
transmission loss and a high geometry precision and is inexpensive
can be formed. Since the relative dielectric constant of the
dielectric strip is higher than those of resin materials such as
Teflon, even if a supporting jig, a circuit board, and the like are
made of these resin material and are provided in vicinity of the
dielectric strip, the dielectric strip is unlikely to be influenced
thereby.
[0407] Preferably, a mole ratio composition formula of the multiple
oxide may be expressed by xMgO.yAl.sub.2O.sub.3z.zSiO.sub.2 where
x=10 to 40 mole percent, y=10 to 40 mole percent, z=20 to 80 mole
percent, and x+y+z=100 mole percent.
[0408] With such a multiple oxide, a NRD guide which has an even
smaller transmission loss and a higher geometry precision and is
more inexpensive can be fabricated.
[0409] Preferably, the dielectric strip may be joined with at least
one of the parallel plate conductors by a solder.
[0410] The pair of parallel plate conductors and the dielectric
strip can be more precisely positioned by joining them by the
solder, thereby improving the heat resistance and durability
reliability of the NRD guide.
[0411] Preferably, the dielectric strip may be made of ceramics, a
glass or glass ceramics. This enables joining by the solder,
thereby improving the heat resistance and durability reliability of
the NRD guide.
[0412] Preferably, the dielectric strip may have a metallic layer
formed on its outer surface to be joined with the parallel plate
conductor by the solder. This facilitates joining of the dielectric
strip by the solder.
[0413] Preferably, the solder may contain at one element selected
from the group consisting of Au, Ti, Sn, Pb. This facilitates
joining of the dielectric strip by the solder.
[0414] Preferably, the metallic layer may be formed of a metallic
foil. This facilitates formation of the metallic layer and joining
of the dielectric strip by the solder.
[0415] Preferably, the suppressor for attenuating electromagnetic
waves of unnecessary modes which is obtained by integrally forming
a conductive layer inside the ceramics dielectric strip by
simultaneous sintering may be connected with one end of the
dielectric strip between the pair of parallel plate conductors.
With such a construction, the dimensional precision and positional
precision of the conductive layers can be improved, and the
suppressor having a stable function can be constructed.
[0416] Preferably, the ceramic dielectric strip may be made of
glass ceramics and the conductive layer is made of a low-resistance
metallic conductor. This facilitates formation of the metallic
layer and can construct the suppressor having a stable
function.
[0417] Preferably, the suppressor for attenuating electromagnetic
waves of unnecessary modes may be provided at one end of the
dielectric strip between the pair of parallel plate conductors, and
formed by providing a plurality of conducive layers at specified
intervals in a plane parallel to a transmission direction of the
high-frequency signal inside the end of the dielectric strip.
[0418] With this construction, resonance of the unnecessary modes
do not occur by separating the conductive layers from each other.
As a result, the unnecessary modes such as the LSE mode can be
effectively attenuated. Further, since the conductive layers are
formed thinner as compared with conductive pins or the like,
reflection by the conductive layers of the LSM mode or the like
which is a transmission mode is unlikely to occur and, therefore,
the transmission loss can be reduced.
[0419] Preferably, a dimension of each conductive layer along the
transmission direction may be equal to or shorter than half the
wavelength of a TEM mode electromagnetic wave of the high-frequency
signal, and a thickness thereof is 0.1 mm or smaller.
[0420] With such conductive layers, electromagnetic waves of the
LSE mode and other unnecessary modes can be effectively attenuated,
and a transmission loss by the conductive layers of the LSM mode
which is a transmission mode can be significantly reduced.
[0421] Preferably a circulator made of two ferromagnetic plates
opposed to each other in the same direction as the pair of parallel
plate conductors being spaced apart may be provided between the
pair of parallel plate conductors, the dielectric strips includes a
plurality of dielectric strips substantially radially arranged with
respect to the circulator, suppressors for blocking electromagnetic
waves of unnecessary modes are provided at the leading ends of the
respective dielectric strips toward the circulator, and impedance
matching members having a relative dielectric constant different
from that of the respective dielectric strips are arranged at the
leading ends of the respective suppressors toward the
circulator.
[0422] With this construction, by providing the impedance matching
members having a relative dielectric constant different from that
of the dielectric strip, electromagnetic waves are becoming
difficult to reflect. As a result, the insertion loss and isolation
characteristic of the high-frequency signal in a high-frequency
band are further improved to significantly widen a range of the
band.
[0423] Preferably, the impedance matching members may be formed at
their sides toward the respective parallel plate conductors with
stepped portions having a height substantially equal to the
thickness of the respective ferromagnetic plates forming the
circulator, and the impedance matching members and the circulator
are connected by holding the impedance matching members by the two
ferromagnetic plates at the stepped portions.
[0424] With this construction, the suppressor and the ferromagnetic
plates are positioned with an improved precision, the circulator
can be assembled with an improved repeatability, and the two
ferromagnetic plates are unlikely to become eccentric with respect
to each other. This enables a circulator characteristic to be
stably obtained with a good repeatability and simplifies
production, presenting a suitable mass-productivity.
[0425] Preferably, there may be further provided a metallic
waveguide connected with the dielectric strip by having an open
termination connected with an opening formed in at least one of
parallel plate conductors in a position corresponding to where an
electric field of a standing wave of LSM mode transmitting in the
dielectric strip is at maximum. With this arrangement, the
dielectric strip and the metallic waveguide can be connected to
reduce a connection loss and a transmission loss, and can be made
smaller.
[0426] Preferably, at least one of the pair of parallel plate
conductors may be formed with an opening in a position
corresponding to where an electric field of a standing wave of LSM
mode transmitting in the dielectric strip is at maximum, and a
metallic waveguide having a closed termination at one end and an
open termination at the other end and formed with an opening in a
position which is distanced from the closed termination by n/2+1/4
(n is zero or a positive integer) of a guide wavelength is
connected with the dielectric strip by coupling the opening of the
parallel plate conductor to that of the metallic waveguide.
[0427] With this construction, the side surfaces of the metallic
waveguide can be placed in parallel to the surfaces of the parallel
plate conductors, with the result that the metallic waveguide can
be firmly placed by improving its connection strength, and the
entire NRD guide can be made thinner. Thus, the NRD guide can be
arranged in a narrow space by being vertically placed. Further, by
connecting the metallic waveguide in a position closest to its
closed termination where the intensity of the electric field is at
maximum, a connection loss can be minimized, and electromagnetic
waves propagate only in a direction toward the open termination in
the metallic waveguide. As a result, a transmission loss can also
be minimized.
[0428] Preferably, the dielectric strip may be widened in an area
extending from a portion corresponding to the opening of the
parallel plate conductor to the open termination than an other
portion.
[0429] Then, the dielectric strip can be made smaller by shortening
its length. Further, since a guide wavelength is shortened in the
widened portion of the dielectric strip, a portion where the
intensity of the electric field is at maximum is shifted in such a
direction as to shorten the dielectric strip, enabling further
miniaturization of the dielectric strip.
[0430] Preferably, an open antenna or flat antenna may be provided
at the open termination of the metallic waveguide which is not
coupled to the opening of the parallel plate conductor. Such an
antenna enables transmission and reception of the high-frequency
signal as a radio wave to and from the outside. Thus, the NRD guide
can be applied to a millimeter wave radar system installed in an
automotive vehicle or the like having a high-efficiency
transmission characteristic.
[0431] An inventive millimeter wave transmitting/receiving
apparatus comprises a pair of parallel plate conductors opposed to
each other at a spacing equal to or shorter than half the
wavelength of the high-frequency signal to be transmitted; the
circulator made of two ferromagnetic plates provided between the
pair of parallel plate conductors and opposed to each other in the
same direction as the pair of parallel plate conductors are spaced
apart; the first dielectric strip arranged between the pair of
parallel plate conductors; the millimeter wave signal oscillator
provided at one end of the first dielectric strip for outputting a
millimeter wave signal to be transmitted; the second dielectric
strip connected with the one end of the first dielectric strip and
radially arranged with respect to the circulator between the pair
of parallel plate conductors; the third dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors and having the transmitting/receiving
antenna at its leading end; the fourth dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; the first, second, third and fourth
suppressors arranged between the one end of the first dielectric
strip and the millimeter wave signal oscillator and between the
second, third and fourth dielectric strips and the circulator, and
formed by arranging a plurality of conductive layers at specified
intervals in a plane parallel to the transmission direction of the
high-frequency signal inside the ends of the respective dielectric
strips; and the mixer for mixing part of the millimeter wave signal
outputted from the millimeter wave signal oscillator and a radio
wave received by the transmitting/receiving antenna to generate an
intermediate-frequency signal by coupling the intermediate position
of the first dielectric strip and that of the fourth dielectric
strip to each other.
[0432] With this construction, the electromagnetic waves of the LSE
mode or the like which is an unnecessary mode can be effectively
attenuated, and the transmission loss of the electromagnetic waves
of the LSM mode which is a transmission mode is reduced. Further,
since part of the transmitted wave is introduced to the mixer via
the circulator to a reduced degree, an excellent transmission
characteristic of the millimeter wave signal is obtained and noise
of the received wave is reduced to increase a detection distance in
the case that this millimeter wave transmitting/receiving apparatus
is applied to a millimeter wave radar or the like.
[0433] Preferably, in the above millimeter wave
transmitting/receiving apparatus, the dimension of each conductive
layer of the suppressor along the transmission direction may be
equal to or shorter than half-the wavelength of the TEM mode
electromagnetic wave of the high-frequency signal, and the
thickness thereof is 0.1 mm or smaller.
[0434] With such conductive layers, electromagnetic waves of the
unnecessary modes such as the LSE mode can be effectively
attenuated, and the transmission loss by the conductive layers of
the LSM mode which is a transmission mode can be significantly
reduced.
[0435] Another inventive millimeter wave transmitting/receiving
apparatus comprises a pair of parallel plate conductors opposed to
each other at a spacing equal to or shorter than half the
wavelength of the high-frequency signal to be transmitted; the
circulator made of two ferromagnetic plates provided between the
pair of parallel plate conductors and opposed to each other in the
same direction as the pair of parallel plate conductors are spaced
apart; the first dielectric strip radially arranged with respect to
the circulator between the pair of parallel plate conductors; the
millimeter wave signal oscillator provided at one end of the first
dielectric strip for outputting a millimeter wave signal to be
transmitted; a second dielectric strip radially arranged with
respect to the circulator between the pair of parallel plate
conductors and having a transmitting antenna at its leading end;
the third dielectric strip radially arranged with respect to the
circulator between the pair of parallel plate conductors; first,
second, third and fourth suppressors arranged between one end of
the first dielectric strip and the millimeter wave signal
oscillator and between the first, second and third dielectric
strips and the circulator, and formed by arranging a plurality of
conductive layers at specified intervals in a plane parallel to the
transmission direction of the high-frequency signal inside the ends
of the respective dielectric strips; the fourth dielectric strip
having one end connected with the first or second dielectric strip
between the pair of parallel plate conductors for transmitting part
of the millimeter wave signal outputted from the millimeter wave
signal oscillator; the fifth dielectric strip arranged between the
pair of parallel plate conductors and having the receiving antenna
at its leading end; and the mixer for mixing part of the millimeter
wave signal outputted from the millimeter wave signal oscillator
and a radio wave received by the receiving antenna to generate an
intermediate-frequency signal by coupling the intermediate position
of the fourth dielectric strip and that of the fifth dielectric
strip to each other.
[0436] With this construction, the electromagnetic waves of the LSE
mode or the like which is an unnecessary mode can be effectively
attenuated, and the transmission loss of the electromagnetic waves
of the LSM mode or the like is reduced. Further, the millimeter
wave signal received by the transmitting antenna is not introduced
to the millimeter wave signal oscillator. Accordingly, an excellent
transmission characteristic of the millimeter wave signal is
obtained and noise caused by oscillation is reduced to increase a
detection distance in the case that this millimeter wave
transmitting/receiving apparatus is applied to a millimeter wave
radar module.
[0437] Preferably, in the above millimeter wave
transmitting/receiving apparatus, the dimension of each conductive
layer of the suppressor along the transmission direction may be
equal to or shorter than half the wavelength of the TEM mode
electromagnetic wave of the high-frequency signal, and the
thickness thereof is 0.1 mm or smaller. With such conductive
layers, electromagnetic waves of the unnecessary modes such as the
LSE mode can be effectively attenuated, and the transmission loss
by the conductive layers of the LSM mode which is a transmission
mode can be significantly reduced.
[0438] Further another inventive millimeter wave
transmitting/receiving apparatus comprises a pair of parallel plate
conductors opposed to each other at a spacing equal to or shorter
than half the wavelength of a millimeter wave signal to be
transmitted; a circulator made of two ferromagnetic plates provided
between the pair of parallel plate conductors and opposed to each
other in the same direction as the pair of parallel plate
conductors being spaced apart; a first dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; a millimeter wave signal oscillator
provided at one end of the second dielectric strip for outputting
the millimeter wave signal to be transmitted; a second dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors, and having a
transmitting/receiving antenna at it leading end; a third
dielectric strip radially arranged with respect to the circulator
between the pair of parallel plate conductors; a fourth dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors, and having one end connected
with the first dielectric strip; first, second and third
suppressors arranged between the first, second and third dielectric
strips and the circulator for suppressing electromagnetic waves of
unnecessary modes; first, second and third impedance matching
members arranged at the end faces of the first, second and third
suppressors toward the circulator and having a relative dielectric
constant different from that of the first, second and third
dielectric strips; and a mixer for mixing part of the millimeter
wave signal outputted from the millimeter wave signal oscillator
and having transmitted in the fourth dielectric strip and a radio
wave received by the transmitting/receiving antenna to generate an
intermediate-frequency signal and transmitted in the third
dielectric strip by coupling an intermediate position of the third
dielectric strip and that of the fourth dielectric strip to each
other.
[0439] With this construction, the transmission loss and isolation
characteristic of the millimeter wave signal in a high-frequency
band having a wide range are further improved, with the result that
a detection distance can be increased in the case that this
millimeter wave transmitting/receiving apparatus is applied to a
millimeter wave radar or the like.
[0440] Preferably, in the above millimeter wave
transmitting/receiving apparatus, the impedance matching members
may be formed at their sides toward the respective parallel plate
conductors with stepped portions having a height substantially
equal to the thickness of the respective ferromagnetic plates
forming the circulator, and the impedance matching members and the
circulator are connected by holding the impedance matching members
by the two ferromagnetic plates at the stepped portions.
[0441] With this construction, the suppressor and the ferromagnetic
plates are positioned with an improved precision, the circulator
can be assembled with an improved repeatability, and the two
ferromagnetic plates are unlikely to become eccentric with respect
to each other. This enables a circulator characteristic to be
stably obtained with a good repeatability and simplifies
production, presenting a suitable mass-productivity.
[0442] Still another inventive millimeter wave
transmitting/receiving apparatus comprises a pair of parallel plate
conductors opposed to each other at a spacing equal to or shorter
than half the wavelength of the millimeter wave signal to be
transmitted; the circulator made of two ferromagnetic plates
provided between the pair of parallel plate conductors and opposed
to each other in the same direction as the pair of parallel plate
conductors are spaced apart; the first dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; the millimeter wave signal oscillator
provided at one end of the first dielectric strip for outputting
the millimeter wave signal to be transmitted; the second dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors and having the transmitting
antenna at its leading end; the third dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; the first, second and third suppressors
arranged between the first, second, and third dielectric strips and
the circulator for suppressing electromagnetic waves of unnecessary
modes; the first, second and third impedance matching members
arranged at the end faces of the first, second and third
suppressors toward the circulator and having a relative dielectric
constant different from that of the second, third and fourth
dielectric strips; the fourth dielectric strip having one end
connected with the first dielectric strip between the pair of
parallel plate conductors for transmitting part of the millimeter
wave signal outputted from the millimeter wave signal oscillator;
the fifth dielectric strip arranged between the pair of parallel
plate conductors and having the receiving antenna at its leading
end; and the mixer for mixing part of the millimeter wave signal
outputted from the millimeter wave signal oscillator and a radio
wave received by the receiving antenna to generate an
intermediate-frequency signal by coupling the intermediate position
of the fourth dielectric strip and that of the fifth dielectric
strip to each other.
[0443] With this construction, the transmission loss and isolation
characteristic of the millimeter wave signal in a high-frequency
band having a wide range are further improved. Further, the
millimeter wave signal to be transmitted is not introduced to the
mixer via the circulator. Accordingly, noise of the received signal
is reduced to increase a detection distance, and an excellent
transmission characteristic of the millimeter wave signal further
increases the detection distance of a millimeter wave radar in the
case that this millimeter wave transmitting/receiving apparatus is
applied to a millimeter wave radar module.
[0444] Preferably, in the above millimeter wave
transmitting/receiving apparatus, the impedance matching members
may be formed at their sides toward the respective parallel plate
conductors with stepped portions having a height substantially
equal to the thickness of the respective ferromagnetic plates
forming the circulator, and the impedance matching members and the
circulator are connected by holding the impedance matching members
by the two ferromagnetic plates at the stepped portions.
[0445] With this construction, the suppressor and the ferromagnetic
plates are positioned with an improved precision, the circulator
can be assembled with an improved repeatability, and the two
ferromagnetic plates are unlikely to become eccentric with respect
to each other. This enables a circulator characteristic to be
stably obtained with a good repeatability and simplifies
production, presenting a suitable mass-productivity.
[0446] Further another inventive millimeter wave
transmitting/receiving apparatus comprises a pair of parallel plate
conductors opposed to each other at a spacing equal to or shorter
than half the wavelength of a millimeter wave signal to be
transmitted; a circulator made of two ferromagnetic plates provided
between the pair of parallel plate conductors and opposed to each
other in the same direction as the pair of parallel plate
conductors being spaced apart; a first dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; a millimeter wave signal oscillator
provided at one end of the first dielectric strip for outputting
the millimeter wave signal to be transmitted; a second dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors; a third dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors; a fourth dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; a metallic waveguide having an open
termination at one end connected with an opening formed in at least
one of the pair of parallel plate conductors in a position
corresponding to where the electric field of a standing wave of LSM
mode transmitting in the third dielectric strip is at maximum while
having an open termination at the other end provided with a
transmitting/receiving antenna; a mixer for mixing part of the
millimeter wave signal from the millimeter wave signal oscillator
having transmitted in the fourth dielectric strip and a radio wave
having transmitted in the third dielectric strip and received by
the transmitting/receiving antenna to generate an
intermediate-frequency signal by coupling an intermediate position
of the third dielectric strip and that of the fourth dielectric
strip to each other.
[0447] With this construction, an excellent transmission
characteristic of the millimeter wave signal can be obtained, which
in turn increases a detection distance of a millimeter wave
radar.
[0448] Still further inventive millimeter wave
transmitting/receiving apparatus comprises a pair of parallel plate
conductors opposed to each other at a spacing equal to or shorter
than half the wavelength of a millimeter wave signal to be
transmitted; a circulator made of two ferromagnetic plates provided
between the pair of parallel plate conductors and opposed to each
other in the same direction as the pair of parallel plate
conductors being spaced apart; a first dielectric strip radially
arranged with respect to the circulator between the pair of
parallel plate conductors; a millimeter wave signal oscillator
provided at one end of the second dielectric strip for outputting
the millimeter wave signal to be transmitted; a second dielectric
strip radially arranged with respect to the circulator between the
pair of parallel plate conductors; a third dielectric strip
radially arranged with respect to the circulator between the pair
of parallel plate conductors; a fourth dielectric strip having one
end connected with the first dielectric strip between the pair of
parallel plate conductors for transmitting part of the millimeter
wave signal outputted from the millimeter wave signal oscillator; a
fifth dielectric strip arranged between the pair of parallel plate
conductors; a first metallic waveguide having an open termination
at one end connected with an opening formed in at least one of the
pair of parallel plate conductors in a position corresponding to
where the electric field of a standing wave of LSM mode
transmitting in the second dielectric strip is at maximum while
having an open termination at the other end provided with a
transmitting antenna; a second metallic waveguide having an open
termination at one end connected with an opening formed in at least
one of the pair of parallel plate conductors in a position
corresponding to where the electric field of a standing wave of LSM
mode transmitting in the fifth dielectric strip is at maximum while
having an open termination at the other end provided with a
receiving antenna; and a mixer for mixing part of the millimeter
wave signal outputted from the millimeter wave signal oscillator
and a radio wave received by the receiving antenna to generate an
intermediate-frequency signal by coupling an intermediate position
of the fourth dielectric strip and that of the fifth dielectric
strip to each other.
[0449] With this construction, the millimeter wave signal to be
transmitted is not introduced to the mixer via the circulator. As a
result, noise of the received signal is reduced to increase a
detection distance, and an excellent transmission characteristic of
the millimeter wave signal further increases the detection distance
of a millimeter wave.
[0450] As this invention may be embodied in several forms without
departing from the spirit of essential characteristics thereof, the
present embodiment is therefore illustrative and not restrictive,
since the scope of the invention is defined by the appended claims
rather than by the description preceding them, and all changes that
fall within metes and bounds of the claims, or equivalence of such
metes and bounds are therefore intended to embraced by the
claims.
* * * * *