U.S. patent application number 09/729038 was filed with the patent office on 2001-09-27 for dielectric waveguide resonator, dielectric waveguide filter, and method of adjusting the characteristics thereof.
This patent application is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Arakawa, Shigeji, Tsunoda, Kikuo.
Application Number | 20010024147 09/729038 |
Document ID | / |
Family ID | 27318001 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024147 |
Kind Code |
A1 |
Arakawa, Shigeji ; et
al. |
September 27, 2001 |
Dielectric waveguide resonator, dielectric waveguide filter, and
method of adjusting the characteristics thereof
Abstract
A dielectric duplexer or multiplexer in which a conducting film
is formed on a dielectric block in a dielectric waveguide
resonator, and a through-hole is formed in the dielectric block.
The unloaded Q is set by selecting the outside dimensions of the
dielectric block. The resonance frequency is set by selecting the
size and location of the through-hole as well as the outside
dimensions of the dielectric block. A terminal electrode is formed
on the outer surface of the dielectric block. A coupling hole is
formed in the dielectric block and a coupling electrode is formed
on the inner surface of the coupling hole. One end of the coupling
electrode is connected to the terminal electrode and the other end
of the coupling electrode is either connected to the conducting
film formed on the outer surface of the dielectric block or
terminated inside the dielectric block. The above structure allows
an increase in the degree of freedom in the design of the
characteristics including the resonance frequency and unloaded Q of
the dielectric waveguide resonator. The invention also provides a
dielectric waveguide filter with a simple coupling mechanism
whereby it is possible to couple to an external circuit without
having to use an additional member and without electromagnetic
leakage.
Inventors: |
Arakawa, Shigeji;
(Kanazawa-shi, JP) ; Tsunoda, Kikuo; (Nomi-gun,
JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Assignee: |
Murata Manufacturing Co.,
Ltd.
|
Family ID: |
27318001 |
Appl. No.: |
09/729038 |
Filed: |
December 4, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09729038 |
Dec 4, 2000 |
|
|
|
09464154 |
Dec 16, 1999 |
|
|
|
09464154 |
Dec 16, 1999 |
|
|
|
08871333 |
Jun 9, 1997 |
|
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|
6020800 |
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|
Current U.S.
Class: |
333/135 ;
333/208 |
Current CPC
Class: |
H01P 7/06 20130101; Y02B
20/22 20130101; H01P 7/04 20130101; H01P 7/10 20130101; H01P 1/2056
20130101; Y02B 20/00 20130101; H01P 1/2088 20130101 |
Class at
Publication: |
333/135 ;
333/208 |
International
Class: |
H01P 001/213; H01P
001/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 1996 |
JP |
8-147112 |
Jul 23, 1996 |
JP |
8-193178 |
May 29, 1997 |
JP |
9-140116 |
Claims
What is claimed is:
1. A multi-terminal dielectric waveguide filter comprising: a
dielectric block having an outer surface covered with a conductive
film, a pair of end surfaces, first and second opposing side
surfaces extending between said end surfaces, and third and fourth
opposing side surfaces extending between said first and second side
surfaces; a plurality of resonance holes formed in said dielectric
block extending between said first and second side surfaces, inner
surfaces of said resonance holes being substantially free of
conductive material, each said resonance hole defining a resonator;
a plurality of slots formed respectively in said third and fourth
side surfaces, at locations along said dielectric block between
respective pairs of said resonance holes, and covered by said
conductive film; a plurality of coupling holes formed in said
dielectric block extending from said first side surface and
comprising a conductive material so as to provide coupling
electrodes which are electromagnetically coupled to respective ones
of said resonance holes; and a plurality of terminals connected
respectively to said plurality of coupling holes.
2. A multi-terminal dielectric waveguide filter according to claim
1, wherein said conductive material in said coupling holes is
provided by conductive films on respective inner surfaces of said
coupling holes.
3. A multi-terminal dielectric waveguide filter according to claim
2, wherein said coupling holes extend between said first and second
side surfaces and generally parallel to said resonance holes.
4. A multi-terminal dielectric waveguide filter according to claim
2, wherein said coupling electrodes are connected to respective
terminal electrodes on said first side surface.
5. A multi-terminal dielectric waveguide filter according to claim
4, wherein said coupling holes extend between said first and second
side surfaces and generally parallel to said resonance holes.
6. A multi-terminal dielectric waveguide filter according to claim
1, wherein said multi-terminal dielectric waveguide filter has TE
mode resonance.
7. A multi-terminal dielectric waveguide filter according to claim
6, wherein said TE mode is TE101 mode
8. A dielectric waveguide filter according to claim 1, wherein said
dielectric waveguide filter has TE-mode resonance with magnetic
coupling via a coupling loop defined by said coupling electrodes
and by said conducting film on said dielectric block.
9. A dielectric waveguide filter according to claim 8, wherein said
TE mode is TE101 mode.
10. A dielectric waveguide duplexer comprising: a dielectric block
having an outer surface covered with a conductive film, a pair of
end surfaces, first and second opposing side surfaces extending
between said end surfaces, and third and fourth opposing side
surfaces extending between said first and second side surfaces; a
plurality of resonance holes formed in said dielectric block
extending between said first and second side surfaces, inner
surfaces of said resonance holes being substantially free of
conductive material, each said resonance hole defining a resonator;
a plurality of slots formed respectively in said third and fourth
side surfaces, at locations along said dielectric block between
respective pairs of said resonance holes, and covered by said
conductive film; wherein a first group of said resonators define a
first filter and a second group of said resonators define a second
filter; a plurality of coupling holes formed in said dielectric
block extending from said first side surface and comprising a
conductive material so as to provide coupling electrodes which are
electromagnetically coupled to respective ones of said resonators;
wherein a first one of said coupling holes is coupled to a
respective resonator of said first filter, a second one of said
coupling holes is coupled to a respective resonator of said second
filter, and a third one of said coupling holes is coupled in common
to respective resonators of both of said first and second filters;
and first, second and third terminals connected respectively to
said first, second and third coupling holes.
11. A multi-terminal dielectric waveguide filter according to claim
10, wherein said conductive material in said coupling holes is
provided by conductive films on respective inner surfaces of said
coupling holes.
12. A multi-terminal dielectric waveguide filter according to claim
11, wherein said coupling holes extend between said first and
second side surfaces and generally parallel to said resonance
holes.
13. A multi-terminal dielectric waveguide filter according to claim
11, wherein said coupling electrodes are connected to respective
terminal electrodes on said first side surface.
14. A multi-terminal dielectric waveguide filter according to claim
13, wherein said coupling holes extend between said first and
second side surfaces and generally parallel to said resonance
holes.
15. A multi-terminal dielectric waveguide filter according to claim
10, wherein said multi-terminal dielectric waveguide filter has TE
mode resonance.
16. A multi-terminal dielectric waveguide filter according to claim
15, wherein said TE mode is TE101 mode
17. A dielectric waveguide filter according to claim 10, wherein
said dielectric waveguide filter has TE-mode resonance with
magnetic coupling via a coupling loop defined by said coupling
electrodes and by said conducting film on said dielectric
block.
18. A dielectric waveguide filter according to claim 17, wherein
said TE mode is TE101 mode.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a division of Ser. No. 09/464,154 filed Dec. 16,
1999, allowed, which is a division of Ser. No. 08/871,333 filed
Jun. 9, 1997, now U.S. Pat. No. 6,020,800, the disclosures of which
are incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a dielectric waveguide
resonator and a dielectric waveguide filter for use particularly in
a microwave or millimeter wave range, and to a method of adjusting
the characteristics thereof.
[0004] 2. Description of the Related Art
[0005] There are various types of dielectric resonators known for
use in the microwave range. They include: a TE01.delta.-mode
dielectric resonator consisting of a dielectric in the form of a
solid circular cylinder or a hollow circular cylinder placed in a
shield case; a TM110-mode dielectric resonator consisting of a
prism-shaped dielectric which is placed in a metallic case or a
case covered with a conducting film in such a manner that the
dielectric extends from the upper to the lower faces of the case;
and a TEM-mode dielectric resonator consisting of a dielectric
wherein an inner conductor is disposed in the dielectric and the
outer surface of the dielectric is covered with an outer conductor.
These dielectric resonators have their own features and advantages
and are used as microwave devices in various applications depending
on particular purposes.
[0006] The size of these dielectric resonators can be reduced by
confining the majority of resonating energy into a dielectric
member and furthermore by forming a magnetic wall at a location
close to a boundary plane between the dielectric member and air in
such a manner that the magnetic wall is coincident with the
even-mode symmetric plane. In these dielectric resonators, the
resonance frequency and unloaded Q are determined by the size,
shape, and dielectric constant of the dielectric resonator and the
metallic case, and also by the location of the dielectric member in
the metallic case.
[0007] In the case of a dielectric waveguide resonator consisting
of a dielectric material such as a ceramic dielectric whose outer
surface is covered with a conducting film, its size can be reduced
by a factor of 1/{square root}{square root over (.epsilon..sub.r)}
relative to the size of a resonator in the form of a waveguide
cavity where .epsilon..sub.r is the dielectric constant of the
dielectric material. Thus, the dielectric waveguide resonator is
expected to find applications in small-sized low-loss filters in
the microwave and millimeter wave ranges. When a dielectric
waveguide filter of such a type is combined with a microstrip line
or a similar circuit element, the coupling between the dielectric
waveguide filter and the external circuit is achieved by means of a
structure such as those shown in FIGS. 33-35. In the example shown
in FIG. 33, a conducting film 2 is formed on the outer surface of a
dielectric block I so that the middle part of the dielectric block
1 serves as a waveguide system with a high Q, and coaxial TEM
resonators are formed at either end of the dielectric block 1. In
the example shown in FIG. 34, a conducting film 2 and stubs 9 are
formed on the outer surface of a dielectric block wherein the
coupling to the waveguide resonator system and the coupling to an
external microstrip line are achieved via the stubs 9. In the
example shown in FIG. 35, a hole is formed in a particular side of
a dielectric block 1, and a probe 10 is inserted into the hole
thereby achieving coupling to a waveguide resonance mode.
[0008] In the above-described conventional structures of dielectric
resonators which operate in the TE01.delta., TM110, or TEM mode,
the resonance frequency and unloaded Q can be rather easily set to
desired values by properly selecting the external dimensions.
However, these dielectric resonators have problems in design and
production arising from their structure. That is, in the
TE01.delta.-mode dielectric resonator, a complicated structure is
required to dispose a dielectric resonator at a particular fixed
location in a shield case. In the case of the TM110-mode dielectric
resonator, it is not easy to connect a prism-shaped dielectric to a
metallic case or a case covered with a conducting film through
which a current flows. When the prism-shaped dielectric and the
outer conductor are combined in an integral fashion, a complicated
and difficult molding technique is required. Furthermore, it is
required that an end of the case be open so as to process the
prism-shaped dielectric in the case. When the resonator is used, it
is required to cover the open end with a conductor. This causes an
increase in the cost of the production and assembly process. On the
other hand, in the case of a TEM-mode dielectric resonator, the
outside dimensions should be great enough to obtain a high unloaded
Q. However, if the outside dimensions are increased, the resonance
frequency in a high-order resonance mode becomes close to the
primary resonance frequency in the TEM mode to be used. Since only
a certain number of dielectric materials are available in practical
production, the unloaded Q is limited within a certain range. In
the case where a band-pass filter is constructed of a dielectric
block having a plurality of inner conductor holes and having a
coupling hole formed in the middle of each inner conductor hole
wherein the coupling between resonators is adjusted by properly
selecting the effective dielectric constant between resonators, it
is required that only the inner surface of each inner conductor
hole be covered with an inner conductor while the inner surface of
the coupling holes should remain uncovered. However, this requires
a complicated production process.
[0009] It is also known in the art to construct a dielectric
waveguide resonator by forming a conducting film on the outer
surface of a ceramic dielectric. This structure is equivalent to a
cavity resonator filled with a dielectric. If a dielectric with a
dielectric constant of .epsilon..sub.r is employed, a reduction in
wavelength occurs and thus it is possible to reduce the total size
of the resonator by a factor equal to 1/{square root}{square root
over (.epsilon..sub.r)}. FIG. 31 illustrates the structure of a
TE101-mode dielectric waveguide resonator. The wavelength inside
the resonator is given by .lambda.g=2ac/{square root}{square root
over (a.sup.2+c.sup.2)}, and this wavelength determines the
resonance frequency. The unloaded Q is determined by the wavelength
.lambda.g, the skin depth .delta. of the conducting film formed on
the surface of the dielectric, and the dimensions a, b, and c of
the dielectric block wherein the unloaded Q increases with the
dimensions a, b, and c. Although this type of dielectric waveguide
resonator requires a greater size for the same resonance frequency
than a coaxial dielectric resonator, it is easy to produce a
resonator having a high unloaded Q. However, in this type of
dielectric waveguide resonator, when the dielectric constant
.epsilon..sub.r of the ceramic dielectric used and the main
resonance frequency as well as adjacent resonance frequency are
given, the dimensions a, b, and c of the resonator are determined
by the given parameters, and the unloaded Q is determined by the
dimensions a, b, and c. This requires the dielectric constant
.epsilon..sub.r of the dielectric material to be within the range
around 20, from 30 to 35, or around 90. In practice, it is
difficult to freely select the dielectric constant. Therefore, when
a desired resonance frequency is achieved using a given dielectric
material, the only parameter allowed to vary to adjust the unloaded
Q is the dimension b. In this case, it is required to properly
select the dimension b while taking into account the effect of the
adjacent resonance frequency on the main resonance frequency. Thus,
this type of resonator is difficult to design and adjust.
[0010] In view of the above, it is an object of the present
invention to provide a dielectric waveguide resonator whose
resonance frequency and unloaded Q can be designed in a more
flexible fashion, and can be easily adjusted to desired values.
[0011] FIG. 33 illustrates the structure of a conventional
dielectric waveguide filter. Although this type of dielectric
waveguide filter can be easily coupled to a microstrip line, the
coaxial resonator portions have a low unloaded Q relative to that
of the waveguide resonator, and thus the overall unloaded Q becomes
low. On the other hand, in the case of the structure shown in FIG.
34, it is required that the length of the stub 9 should be large
enough to achieve strong coupling. However, the long stub 9 can
cause leakage of electromagnetic waves via the gap between the stub
9 and the conducting film 2. The leakage of electromagnetic wave
can cause interference in an external circuit. In the structure
shown in FIG. 35, it is required that a probe 10 should be prepared
separately from the resonator. Furthermore, it is also required to
securely fix the probe 10 relative to the dielectric block 1.
[0012] Thus, it is another object of the present invention to
provide a dielectric waveguide resonator having a simple coupling
circuit element by which coupling to an external circuit can be
achieved without having to use an additional special member and
without causing a great amount of leakage of electromagnetic waves
toward the outside.
SUMMARY OF THE INVENTION
[0013] According to an aspect of the present invention, there is
provided a dielectric waveguide resonator including a dielectric
block whose outer surface is covered with a conducting film, the
dielectric waveguide resonator being characterized in that a
through-hole whose inner surface is not covered with a conducting
film is formed in the dielectric block in such a manner that the
through-hole extends from one face to another face of the
dielectric block or a recess whose inner surface is not covered
with a conducing film is formed on a particular face of the
dielectric block thereby adjusting the resonance frequency and the
unloaded Q. As a result of the formation of the through-hole or
recess whose inner surface is not covered with a conducting film in
the dielectric block, the dielectric constant in the through-hole
or recess becomes different from that of the dielectric block and
resultant perturbation effect on the electric field causes an
increase in the resonance frequency. Therefore, this technique
makes it possible to adjust the resonance frequency by properly
selecting the size and/or location of the through-hole or recess
while keeping the outside dimensions of the dielectric block
constant. Thus, it is possible to set the resonance frequency and
unloaded Q to desired values over wide ranges by properly designing
the outside dimensions of the dielectric block and the size or
location of the through-hole or recess. This makes it possible to
design the unloaded Q in a more flexible fashion.
[0014] In the case of a dielectric waveguide resonator consisting
of a rectangular dielectric block whose outer surface is covered
with a conducting film, such as that shown in FIGS. 32A-32B, if the
dielectric block has a dielectric constant .epsilon..sub.r of 21,
and the size thereof is given by a=23 mm, b=9 mm, and c=18 mm, then
the resonance frequency fo becomes about 2.5 GHz. Although it is
also possible to adjust the resonance frequency fo by removing a
particular portion over an area of for example 2 mm square from the
conducting film on a side face of the dielectric block as shown in
FIG. 32B, a change in the resonance frequency fo as great as about
1000 ppm will occur when a metallic element is placed near the
above removed portion of the conducting film. Such a great change
of 1000 ppm in fo will result in a great change in the
characteristics of the multi-stage filter. In contrast, in the case
where a through-hole whose inner surface is not covered with a
conducting film is formed in a dielectric block as shown in FIG.
32A, only a small change of about 100 ppm occurs in fo when a
metallic element is placed near the open plane of the through-hole.
Furthermore, in the case of the structure shown in FIG. 32B in
which the conducting film on a side face is partially removed,
about a 10% reduction occurs in the unloaded Q. In contrast,
substantially no change in the unloaded Q occurs in the case of the
structure shown in FIG. 32A in which the through-hole whose inner
surface is not covered with a conducting film is formed in the
dielectric block.
[0015] According to another aspect of the present invention, the
through-hole or recess is formed at a location at which the
electric field distribution has a high electric strength in a
particular resonance mode. This makes it possible to produce a
relatively great change in the resonance frequency by forming a
small through-hole or recess. This technique also makes it possible
to design the unloaded Q within an expanded range.
[0016] When a resonator can have a plurality of resonance modes, it
is possible to construct a plurality of dielectric resonators with
a single dielectric block by utilizing the individual resonance
modes, and it is also possible to combine these resonance modes to
realize a filter. For example, when the dielectric resonator has
first and second resonance modes, if the through-hole or recess is
formed at a location at which the electric field strength in the
second resonance mode is greater than that in the first resonance
mode, it is possible to adjust selectively only the resonance
frequency in the second resonance mode relative to the resonance
frequency in the first resonance mode even in the case where the
resonance frequencies in the first and second resonance modes are
close to each other. Thus, this technique makes it easy to adjust
the difference in resonance frequency between two resonance modes.
According to another aspect of the present invention, the
through-hole or recess is preferably formed at a location at which
the electric field strength in the first resonance mode is nearly
equal to that in the second resonance mode. In this case, the
resonance frequencies in the first and second resonance modes are
equally affected by the through-hole or recess and thus it is
possible to simultaneously set the resonance frequencies in the two
resonance modes to desired values simply by adjusting the single
through-hole or recess.
[0017] In still another aspect of the present invention, the two
resonance modes may be degenerated by forming the dielectric block
into a rectangular block shape in which at least two opposite side
faces are squares, or into a solid circular cylinder or hollow
circular cylinder.
[0018] If the through-hole or recess is formed in a direction along
the electric field in a particular resonance mode, it is possible
to enhance the perturbation effect on the electric field.
Furthermore, if the through-hole or recess is formed into a tapered
shape or a stepped shape, it becomes easy to make coarse and fine
adjustments on the resonance frequency by properly forming the
through-hole or recess.
[0019] Although the through-hole or recess may be hollow (that is
filled with air), a dielectric material having a dielectric
constant different from that of the dielectric block may also be
placed in the through-hole or recess.
[0020] In a further aspect of the invention, the opening end of the
through-hole or recess is covered with a conductor thereby ensuring
that leakage of electromagnetic waves toward the outside or
unwanted electromagnetic coupling with an external circuit is
prevented.
[0021] According to another aspect of the present invention, there
is provided a dielectric waveguide filter including a dielectric
block whose outer surface is covered with a conducting film, the
dielectric waveguide filter being characterized in that a terminal
electrode isolated from the conducting film is formed on the outer
surface of the dielectric block and a hole is formed in the
dielectric block wherein a coupling electrode is formed on the
inner surface of the hole in such a manner that one end of the
coupling electrode is connected to the terminal electrode and the
other end of the coupling electrode is connected to the conducting
film. This makes it possible to reduce the leakage of
electromagnetic waves toward the outside without having to use an
additional special member. In this structure a coupling loop is
formed by the coupling electrode and the conducing film disposed on
the outer surface of the dielectric block, thereby providing
magnetic coupling to a resonance mode of the dielectric waveguide
resonator occurs.
[0022] According to another aspect of the invention, a terminal
electrode isolated from the conducting film is formed on the outer
surface of the dielectric block and a hole is formed in the
dielectric block wherein a coupling electrode is formed on the
inner surface of the hole in such a manner that one end of the
coupling electrode is connected to the terminal electrode and the
other end of the coupling electrode is electrically open-circuited
in the hole. In this structure, the coupling electrode serves to
provide coupling to the electric field in a resonance mode of the
dielectric waveguide resonator. In any of these structures
described above, a connection to an external circuit element such
as a microstrip line can be made via the terminal electrode formed
on the outer surface of the dielectric block wherein the terminal
electrode is connected to one end of the coupling electrode. The
above connection can be achieved without having to insert an
additional special member such as a probe into the hole from the
outside. Furthermore, this structure provides excellent coupling to
the external circuit element without producing leakage of
electromagnetic waves toward the outside.
[0023] According to still another aspect of the invention, the
above-described hole includes a hole extending in a substantially
straight line and a hole intersecting the former hole. This makes
it possible to form a coupling electrode in a flexible fashion in
the dielectric block.
[0024] According to another aspect of the invention, a hole whose
inner surface is not covered with a conducting film is formed in
the dielectric block and a pin-shaped conductor covered with an
insulating material is inserted in the above hole so that coupling
with an external circuit is achieved via the pin-shaped conductor.
Thus, this technique allows a simplification of the structure of
the dielectric block and also allows easier coupling to the
external circuit.
[0025] According to still another aspect of the invention, a slot
whose inner surface is covered with a conducting film is formed in
the dielectric block so that the slot acts as a node by which the
dielectric block is divided along the direction of its length. This
technique makes it possible to realize a multi-stage dielectric
waveguide filter with a single dielectric block.
[0026] According to another aspect of the invention, there is
provided a method of adjusting the characteristics of dielectric
waveguide filter, including the step of partially removing the
coupling electrode, which is formed on the inner surface of the
hole, thereby adjusting the amount of coupling to an external
circuit. In this method, it is possible to easily adjust the amount
of coupling to the external circuit simply by partially removing
the coupling electrode without having to use an additional special
adjustment member and without producing leakage of electromagnetic
waves toward the outside.
[0027] According to still another aspect of the invention, there is
provided a method of adjusting the characteristics of dielectric
waveguide filter, including the step of partially removing the
inner surface of the through-hole or recess.
[0028] Other features and advantages of the invention will be
understood from the following detailed description of embodiments
thereof and the accompanying drawings, in which like references
illustrate like elements and parts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIGS. 1A and 1B are respectively a perspective view and a
cross-sectional view illustrating the construction of a dielectric
resonator according to a 1st embodiment of the invention;
[0030] FIG. 2 is a perspective view illustrating the construction
of a dielectric resonator according to a 2nd embodiment of the
invention;
[0031] FIG. 3 is a cross-sectional view illustrating the
construction of a dielectric resonator according to a 3rd
embodiment of the invention;
[0032] FIG. 4 is a perspective view illustrating the construction
of a dielectric resonator according to a 4th embodiment of the
invention;
[0033] FIG. 5 is a perspective view illustrating the construction
of a dielectric resonator according to a 5th embodiment of the
invention;
[0034] FIG. 6 is a perspective view illustrating the construction
of a dielectric resonator according to a 6th embodiment of the
invention;
[0035] FIGS. 7A and 7B are respectively perspective views
illustrating the construction of a dielectric resonator according
to a 7th embodiment of the invention and a modification
thereof;
[0036] FIG. 8 is a perspective view illustrating the construction
of a dielectric resonator according to an 8th embodiment of the
invention;
[0037] FIG. 9 is a perspective view illustrating the construction
of a dielectric resonator according to a 9th embodiment of the
invention;
[0038] FIG. 10 is a perspective view of a dielectric resonator
according to a 10th embodiment of the invention;
[0039] FIGS. 11A and 11B are respectively cross-sectional views of
a dielectric resonator according to a 11th embodiment of the
invention and a modification thereof;
[0040] FIGS. 12A and 12B are respectively cross-sectional views of
a dielectric resonator according to a 12th embodiment of the
invention and a modification thereof;
[0041] FIG. 13 is a cross-sectional view of a dielectric resonator
according to a 13th embodiment of the invention;
[0042] FIG. 14 is a cross-sectional view of a dielectric resonator
according to a 14th embodiment of the invention;
[0043] FIGS. 15A and 15B are perspective views of a dielectric
waveguide filter according to a 15th embodiment of the
invention;
[0044] FIG. 16 is a cross-sectional of the dielectric waveguide
filter according to the 15th embodiment of the invention;
[0045] FIGS. 17A, 17B and 17C are schematic diagrams illustrating
an example of a resonance mode which can occur in the dielectric
waveguide filter according to the 15th embodiment of the
invention;
[0046] FIG. 18 is a perspective view of a dielectric waveguide
filter according to a 16th embodiment of the invention;
[0047] FIGS. 19A and 19B are perspective views of a dielectric
waveguide filter according to a 17th embodiment of the
invention;
[0048] FIGS. 20A and 20B are respectively a perspective view and a
cross-sectional view of a dielectric waveguide filter according to
an 18th embodiment of the invention;
[0049] FIGS. 21A and 21B are cross-sectional views illustrating the
structure of a dielectric waveguide filter and a method of
adjusting the characteristics thereof, according to a 19th
embodiment of the invention;
[0050] FIGS. 22A and 22B are cross-sectional views illustrating the
structure of a dielectric waveguide filter and a method of
adjusting the characteristics thereof, according to a 20th
embodiment of the invention;
[0051] FIG. 23 is a cross-sectional view illustrating the structure
of a dielectric waveguide filter and a method of adjusting the
characteristics thereof, according to a 21st embodiment of the
invention;
[0052] FIG. 24 is a perspective view of a dielectric waveguide
filter according to a 22nd embodiment of the invention;
[0053] FIG. 25 is a cross-sectional view of the dielectric
waveguide filter according to the 22nd embodiment of the
invention;
[0054] FIG. 26 is a perspective view of a dielectric waveguide
filter according to a 23rd embodiment of the invention;
[0055] FIG. 27 is a cross-sectional view of the dielectric
waveguide filter according to the 23rd embodiment of the
invention;
[0056] FIG. 28 is a cross-sectional view of a dielectric waveguide
filter according to a 24th embodiment of the invention;
[0057] FIG. 29 is a cross-sectional view of a dielectric waveguide
filter according to a 25th embodiment of the invention;
[0058] FIG. 30 is a perspective view of a dielectric waveguide
filter according to a 26th embodiment of the invention;
[0059] FIG. 31 is a schematic diagram illustrating the structure of
a conventional dielectric waveguide resonator;
[0060] FIG. 32A and 32B are perspective views illustrating
respective examples of the structure of a dielectric waveguide
resonator;
[0061] FIG. 33 is a perspective view illustrating the structure of
a mechanism for coupling to an external circuit, provided on a
dielectric waveguide resonator according to a conventional
technique;
[0062] FIG. 34 is a perspective view illustrating the structure of
another mechanism for coupling to an external circuit, provided on
a dielectric waveguide resonator according to a conventional
technique; and
[0063] FIG. 35 is a partially cutaway perspective view illustrating
the structure of a mechanism for coupling to an external circuit,
provided on a dielectric waveguide resonator according to a
conventional technique.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0064] FIGS. 1A and 1B illustrate the construction of a dielectric
waveguide resonator (hereinafter referred to simply as a dielectric
resonator) according to a 1st embodiment of the present invention,
wherein FIG. 1A is a perspective view illustrating its external
appearance and FIG. 1B is a cross-sectional view thereof. Reference
numeral 1 denotes a dielectric block in a substantially rectangular
form. A circular through-hole 12 is formed in the center of the
dielectric block 1 and a conducting film 2 is formed on the outer
surface (six side faces) of the dielectric block 1. In FIG. 1A, the
arrows drawn on the sides of the dielectric block 1 represent the
projections of the electric field distribution inside the
dielectric block 1 (in the central portion or near the central
portion) onto the two sides of the dielectric block 1. The actual
internal electric field distribution is similar to that shown in
FIG. 31 wherein the energy of electric field in the vertical
direction in the figure increases with location toward the center
of the dielectric block 1 and decreases with location toward the
periphery of the dielectric block 1 (the electric field strength is
represented by the length of the arrows). In the specific example
shown in FIGS. 1A and 1B, however, the dielectric block 1 has the
through-hole 12 at its center, and thus the electric field strength
inside the through-hole 12 is reduced since the dielectric constant
inside the through-hole 12 is lower than that of the dielectric
block 1.
[0065] If the coordinate system is represented in a similar manner
to that in FIG. 31, the dielectric resonator shown in FIGS. 1A and
1B has a TE101 resonance mode. The outside dimensions a, b, and c
of the dielectric block 1 are selected so that the dielectric block
1 has a desired unloaded Q and has a resonance frequency which is
close to but lower than a desired value. The internal diameter of
the through-hole 12 is set so that the overall resonance frequency
becomes the desired value. The through-hole 12 may be formed when
the dielectric block 1 is molded, or may be formed by means of
drilling before firing the rectangular dielectric ceramic.
Otherwise, after firing the dielectric ceramic, the conducting film
2 is formed and then the through-hole 12 is formed by means of
cutting.
[0066] Although not shown in FIGS. 1A-1B, signal input/output means
may also be provided on the dielectric resonator in such a manner
that a hole is formed in the dielectric block 1 at a location
corresponding to a probe and the inner surface of the hole is
covered with a conducting film, or in such a manner that one end
face of the dielectric block is formed to serve as an electrically
open-circuited end and a driving microstrip line is formed on that
end face.
[0067] FIG. 2 is a perspective view illustrating the appearance of
a dielectric resonator according to a 2nd embodiment of the
invention. As shown in FIG. 2, the dielectric resonator has a
through-hole 12a, similar to the through-hole 12 shown in FIGS.
1A-1B, formed in the center of a dielectric block where the
electric field has a great value. The dielectric resonator further
has a through-hole 12b formed near an end of the dielectric block 1
where the electric field has a rather low value. The formation of
the through-hole 12b with a small inner diameter at a location
where the electric field has a low value makes it possible to
easily make a fine adjustment of the resonance frequency.
[0068] FIG. 3 is a cross-sectional view of a dielectric resonator
according to a 3rd embodiment of the invention. Unlike the
dielectric resonator shown in FIGS. 1A-1B, a recess 14 is formed in
a dielectric block 1 wherein the recess 14 does not extend filly
through the dielectric block 1. In this structure, the resonance
frequency may be adjusted not only by the inner diameter of the
recess 14 but also by the depth of the recess 14. In addition to
the recess 14 formed on the upper surface of the dielectric block
1, another recess may be formed on the lower surface of the
dielectric block 1 so as to form a ridge-type dielectric
resonator.
[0069] FIG. 4 is a perspective view of a dielectric resonator
according to a 4th embodiment of the invention. As is the case in
this 4th embodiment, the dielectric block 1 is not limited to a
rectangular structure but may also be constructed into the form of
a solid circular cylinder or a hollow circular cylinder, wherein
the unloaded Q and an approximate resonance frequency are
determined by the external dimensions of the circular cylinder and
the resonance frequency is adjusted to a final desired value by
forming a through-hole 12.
[0070] FIG. 5 is a schematic diagram illustrating the structure of
a dielectric resonator according to a 5th embodiment of the
invention. This dielectric resonator has two resonance modes
wherein the electric field in the first resonance mode has a
distribution such as that represented by the projection onto a side
of a dielectric block 1 while the projection of the electric field
in the second resonance mode onto the side of the dielectric block
1 is shown by another separate representation. Through-holes 12a
and 12b are formed at locations where the electric field strength
has a similar value and thus these through-holes 12a and 12b have a
similar perturbation effect on the two resonance mode. This means
that the resonance frequency can be adjusted at the same time for
both the first and second resonance modes. Although in the specific
example shown in FIG. 5 two through-holes are formed, only one
through-hole may be formed at either side.
[0071] In the dielectric resonator having two resonance modes shown
in FIG. 5, if a through-hole is formed in the center of the
dielectric block 1, then that through-hole will increase the
resonance frequency in the first mode. However, substantially no
change occurs in the resonance frequency in the second resonance
mode, because the through-hole in the center of the dielectric
block 1 has little perturbation effect on the resonance frequency
in the second resonance mode. Conversely, if a through-hole is
formed at a location where the electric field strength has a large
value for the second resonance mode while the electric field
strength has a low value for the first resonance mode, then the
through-hole has a greater perturbation effect on the electric
field in the second resonance mode and a smaller perturbation
effect on the electric field in the first resonance mode, and
therefore the formation of the through-hole results in an increase
in the resonance frequency in the second resonance mode with
substantially no increase in the resonance frequency in the first
resonance mode. As described above, it is possible to selectively
control the resonance frequency in a particular resonance mode of a
plurality of resonance modes by properly selecting the location of
a through-hole.
[0072] FIG. 6 is a schematic diagram illustrating the structure of
a dielectric resonator according to a 6th embodiment of the
invention. In FIG. 6, arrows drawn on a side of a dielectric block
1 represent the distribution of the electric field in a first
resonance mode while arrows drawn on the upper surface of the
dielectric block 1 represent the distribution of the electric field
in a second resonance mode. In FIG. 6, the representation of the
electric field distributions is given in a simplified fashion
wherein the first resonance mode is for example a TE111 mode and
the second resonance mode is for example a TM111 mode, and these
two resonance modes are degenerated. In this embodiment, a
through-hole 12 is formed at a properly selected location in a
properly-selected direction so that the resonance frequency is
selectively controlled for either first or second resonance mode,
or otherwise at the same time for both the first and second
resonance modes.
[0073] FIGS. 7A-7B illustrate the structure of a dielectric
resonator according to a 7th embodiment of the invention. The
dielectric resonator consists of a dielectric block 1 in the form
of a rectangular block having upper and lower square-shaped
surfaces. The six faces of the dielectric block 1 are all covered
with a conducting film. Arrows drawn on the upper surface of the
dielectric block 1 represent the directions of the electric field
for first and second resonance modes wherein both the first and
second resonance modes are in TE101 modes and thus these two
resonance modes are degenerated. Therefore, the resonance
frequencies in the above two modes are equal to each other. (In
FIGS. 7A-7B, the horizontal directions are defined as the x and y
directions and the vertical direction is defined as the z
direction.) When a through-hole 12 is formed in the center of the
dielectric block 1 along the z direction as shown in FIG. 7A, the
through-hole 12 has the same perturbation effect on the two
resonance modes, and thus the same change occurs in the resonance
frequency in both resonance modes. On the other hand, as shown in
FIG. 7B, if the through-hole 12 is formed at a location shifted
from the center, there will be a difference in the perturbation
effect on the electric field between the two resonance modes and
therefore there will be a difference in the resonance frequency
between the two resonance modes. As a result, the degeneracy is
resolved and the two resonance modes are coupled to each other.
[0074] FIG. 8 is a perspective view of a dielectric resonator
according to an 8th embodiment of the invention. In this 8th
embodiment, unlike the structure shown in FIGS. 7A-7B, a
through-hole 12 is formed in a direction crossing a pair of
rectangular surfaces. In this structure, the through-hole 12 has a
greater perturbation effect on a resonance mode in which the
electric field has a component in a direction parallel to the
through-hole 12 than on the other resonance mode, and the two
resonance modes are coupled to each other. The coupling strength
between the two resonance modes is set to a desired value by
properly selecting the size and the location of the through-hole
12.
[0075] FIG. 9 is a schematic diagram illustrating the structure of
a dielectric resonator according to a 9th embodiment of the
invention. If a conducting film is formed on the outer surface of a
dielectric block 1 in a circular cylinder form such as that shown
in FIG. 9, there will be two resonance modes (in a TE111 mode) in
which electric fields are distributed in such a manner as
represented by the projection of the lines of force onto the upper
surface of the dielectric block 1 (wherein both solid and broken
lines of force represent the distribution of the electric field).
If a through-hole 12 is formed in the dielectric block along the z
axis, the through-hole 12 has a greater perturbation effect on a
resonance mode in which the electric field has a component in a
direction along the through-hole 12 than on the other resonance
mode. This produces a difference in resonance frequency between the
two resonance modes, and the two resonance modes are coupled to
each other.
[0076] FIG. 10 is a schematic diagram illustrating the structure of
a dielectric resonator according to a 10th embodiment of the
invention. This dielectric resonator consists of a dielectric block
1 in the form of a cubic whose six faces are covered with a
conducting film. In this structure, there can be three resonance
modes each having an electric field component in a direction along
one of three axes denoted by arrows in FIG. 10 wherein these three
resonance modes are degenerated. If a through-hole 12 is formed in
the dielectric resonator having such the structure, the
through-hole 12 has a greater perturbation effect on a resonance
mode in which the electric field has a component in a direction
along the through-hole 12 than on the other two resonance modes. As
a result, the above resonance mode has a resonance frequency
different from that in the other two resonance modes.
[0077] FIGS. 11A-11B are cross-sectional views of a dielectric
resonator according to an 11th embodiment of the invention.
Although in the embodiments described above the through-hole of the
dielectric resonator is formed in a circular shape, the
through-hole 12 may also be formed in such a manner that the inner
diameter of the through-hole 12 varies in a stepping fashion with
the location along the depth direction as shown in FIG. 11A, or may
be formed in a tapered fashion in which the inner diameter of the
through-hole 12 gradually varies with the location along the depth
direction as shown in FIG. 11B. In this case, the resonance
frequency is roughly determined by a portion of the through-hole
having a greater inner diameter and is finely adjusted by a portion
having a smaller inner diameter.
[0078] FIGS. 12A-12B are cross-sectional views of a dielectric
resonator according to a 12th embodiment of the invention. In the
structure shown in FIG. 12A, the inside of the through-hole is
filled with a dielectric 15. Alternatively, as shown in FIG. 12B,
the inside of the through-hole may be partially filled with a
dielectric 15. When the dielectric constant of the dielectric 15
filled in the through-hole is greater than the dielectric constant
of the dielectric block 1, the filling of the dielectric 15 results
in a reduction in the resonance frequency. If the resonance
frequency is maintained at a fixed value, the dielectric 15 makes
it possible to reduce the total size of the dielectric resonator.
The resonance frequency of the resonator is determined by the
overall characteristics of the whole elements including the
dielectric 15. For example, if the dielectric 15 has a different
frequency-temperature characteristic from that of the dielectric
block 1, then the frequency-temperature characteristic of the
resonator is determined by the overall frequency-temperature
characteristic of the combination of the dielectric 15 and the
dielectric block 1. Therefore, it is possible to easily improve the
temperature characteristic by properly selecting the dielectric
materials so that the frequency-temperature characteristic of the
dielectric block 1 is compensated for by the frequency-temperature
characteristic of the dielectric 15.
[0079] FIG. 13 is a cross-sectional view of a dielectric resonator
according to a 13th embodiment of the invention. As shown in FIG.
13, the open ends of the through-holes 12 are covered with a
conductor such as copper foil 16 fixed and connected via soldering
to the conducting film 2. The conductors 16 serve to prevent
leakage of electric field from the inside to the outside of the
through-hole 12 and thus cutting off the electromagnetic coupling
to an external circuit.
[0080] FIG. 14 is a cross-sectional view of a dielectric resonator
according to a 14th embodiment of the invention. Unlike the
structure shown in FIG. 13 in which conductors are provided so that
only the open ends of the through-holes are covered with the
conductors, the dielectric resonator of the present embodiment is
placed, as shown in FIG. 14, in a case 17 so that the whole
dielectric resonator is shielded.
[0081] Now referring to FIGS. 15A-17C, the structure of a
dielectric waveguide filter according to a 15th embodiment of the
invention will be described below.
[0082] FIGS. 15A-15B are perspective views of the dielectric
waveguide filter wherein FIG. 15A is a perspective view of the
dielectric waveguide filter mounted on a circuit board and FIG. 15B
is a perspective view of the dielectric waveguide filter placed in
an upside-down fashion. Two through-holes 5 extending in slanted
directions are formed in a rectangular dielectric block 1 and a
coupling electrode 4 is formed on the inner surface of each
through-hole 5. The majority area of the outer surface of the
dielectric block 1 is covered with a conducting film 2 and two
terminal electrodes 3 are disposed on the outer surface of the
dielectric block 1 such that the two terminal electrodes 3 are
isolated from the conducting film 2. One end of the coupling
electrode 4 formed on the inner surface of each through-hole 5 is
connected to the corresponding terminal electrode 3 and the other
end of the coupling electrode is connected to the conducting film
2. FIG. 16 illustrates a cross section extending through the two
through-holes shown in FIG. 15A. FIGS. 17A, 17B and 17C
schematically illustrate a resonance mode wherein FIGS. 17A, 17B,
and 17C are a top view, front view, and side view thereof,
respectively. Arrows and dots denote electric fields and broken
lines denote magnetic fields. In this specific example, resonance
occurs in a TE101 mode in which coupling mainly to a magnetic
component in the resonance mode occurs via a coupling loop formed
by the coupling electrodes 4 and the conducting film 2 on the outer
surface of the dielectric block.
[0083] The through-holes 5 shown in FIGS. 15A-15B may be formed
when the dielectric ceramic is molded, or may be formed by means of
drilling after completion of the molding process or after firing
the dielectric ceramic. The conducting film 2, coupling electrodes
4, and terminal electrodes 3 may be formed by depositing a
conducting film over the entire surface of the dielectric ceramic
by means of a dipping or plating technique, and then patterning the
deposited conducting film by means of etching. Alternatively, the
patterns of the conducting film 2 and terminal electrodes 3 may
also be formed directly by means of screen printing using a
material such as silver paste.
[0084] FIG. 18 is a perspective view of a dielectric waveguide
filter according to a 16th embodiment of the invention. Unlike the
15th embodiment, two through-holes 5 extending in a vertical
direction are formed in a dielectric block and a coupling electrode
4 is formed on the inner surface of each through-hole 5 wherein one
end of each coupling electrode 4 is connected to a corresponding
terminal electrode 3 formed on the outer surface of the dielectric
block 1 and the other end of each coupling electrode 4 is connected
to a conducting film 2 formed on the outer surface of the
dielectric block 1. With this structure, a coupling loop is formed
by the coupling electrodes 4 and the conducting film 2 wherein the
coupling loop provides magnetic coupling with a TE101 resonance
mode.
[0085] FIGS. 19A-19B are perspective views of a dielectric
waveguide filter according to a 17th embodiment of the invention,
wherein FIG. 19A is a perspective view of the dielectric waveguide
filter mounted on a circuit board and FIG. 19B is a perspective
view of the dielectric waveguide placed in an upside-down fashion.
In this embodiment, L-shaped through-holes 5 are formed in a
dielectric block 1 and a coupling electrode 4 is formed on the
inner surface of each L-shaped through-hole 5. A conducting film 2
is formed on the outer surface of the dielectric block 1, and a
terminal electrode 3 is formed on each of two opposing end faces of
the dielectric block 1 in such a manner that each terminal
electrode 3 is isolated from the conducting film 2. One end of each
coupling electrode 4 is connected to the corresponding terminal
electrode 3 and the other end is connected to the conducting film
2. Also in this embodiment, a coupling loop is formed by the
coupling electrodes 2 and the conducting film 2 wherein the
coupling loop provides magnetic coupling with a TE101 resonance
mode.
[0086] The through-holes 5 shown in FIGS. 19A-19B may be formed by
means of so-called lost-wax technique in which after molding a
dielectric ceramic together with an L-shaped wax member, the
L-shaped wax member is removed during a firing process.
[0087] FIGS. 20A and 20B are a perspective view and a
cross-sectional view of a dielectric waveguide filter according to
an 18th embodiment of the invention. Two vertical through-holes 5
are formed in a dielectric block 1 wherein each vertical
through-hole 5 is connected to a horizontal hole 6 extending in a
direction perpendicular to the vertical through-holes 5. A
conducting film 2 and terminal electrodes 3 are formed on the outer
surface of the dielectric block 1. Coupling electrodes 4 are formed
on the inner surfaces of the respective through-holes 5 and holes
6. One end of each coupling electrode 4 formed on the inner surface
of each through-hole 5 is connected to the corresponding terminal
electrode 3, and the other end is connected to the conducting film
2. The outer end of each coupling electrode 4 formed on the inner
surface of each hole 6 is connected to the conducting film 2. In
this structure, the loop area of the coupling loop formed by the
coupling electrodes 4 and the conducting film 2 is determined by
the height at which the holes 6 are formed, and thus the amount of
coupling to an external circuit can be controlled by adjusting the
height at which the holes 6 are formed.
[0088] Now referring to FIGS. 21A, 21B, 22A, 22B and 23, other
possible structures of dielectric waveguide filters and methods of
adjusting the characteristics thereof will be described below.
[0089] FIGS. 21A and 21B are cross-sectional views illustrating the
structure of a dielectric waveguide filter and a method of
adjusting the characteristics thereof, according to a 19th
embodiment of the invention. As in the dielectric waveguide filter
shown in FIG. 18, two vertical through-holes 5 are formed in a
dielectric block 1 and a coupling electrode 4 is formed on the
inner surface of each vertical through-hole 5. One end of each
coupling electrode 4 is connected to a corresponding one of
terminal electrodes 3 formed on the outer surface of the dielectric
block 1. In a specific example shown in FIG. 21A, a hole with a
constant diameter is formed in each through-hole 5 of the
dielectric block by cutting the upper portion of each through-hole
5 down to a predetermined depth using a rotating grindstone or the
like. In the case of an example shown in FIG. 21B, cutting is
performed so that an inner portion of each through-hole 5 is
expanded in diameter. In the present embodiment, the upper ends of
the coupling electrodes 4 are isolated from the conducting film 2
by the above-described cutaway portions 7 formed in the respective
through-holes 5 so that the upper ends of the coupling electrodes 4
are electrically open-circuited and thus the coupling electrodes 4
serve as probes. In this structure, coupling mainly to the electric
field in a resonance mode occurs via the coupling electrodes 4.
Therefore, in this embodiment, the characteristics are adjusted by
properly controlling the cutting amount (depth) of the cutaway
portions 7 thereby controlling the length of the coupling
electrodes 4 thus adjusting the amount of coupling.
[0090] FIGS. 22A and 22B are cross-sectional views illustrating the
structure of a dielectric waveguide filter and a method of
adjusting the characteristics thereof, according to a 20th
embodiment of the invention. As in the dielectric waveguide filter
shown in FIGS. 20A-20B, two vertical through-holes 5 are formed in
a dielectric block 1 wherein each vertical through-hole 5 is
connected to a horizontal hole 6 extending in a direction
perpendicular to the vertical through-holes 5. A conducting film 2
and terminal electrodes 3 are formed on the outer surface of the
dielectric block 1. Coupling electrodes 4 are formed on the
respective inner surfaces of the through-holes 5 and the holes 6.
One end of each coupling electrode 4 formed on the inner surface of
each through-hole 5 is connected to the corresponding terminal
electrode 3, and the outer end of each coupling electrode 4 formed
on the inner surface of each hole 6 is connected to the conducting
film 2. In a specific example shown in FIG. 22A, a hole with a
constant diameter is formed in each through-hole 5 of the
dielectric block by cutting the upper portion of each through-hole
5 to a predetermined depth using a rotating grindstone or the like.
In the case of an example shown in FIG. 22B, cutting is performed
so that an inner portion of each through-hole 5 is expanded in
diameter. Thus, in this embodiment, a similar structure to that of
the dielectric waveguide filter shown in FIGS. 19A-19B is obtained
by forming a cutaway portion 7. The amount of electromagnetic
coupling with the resonance mode is controlled by properly
selecting the cutting amount of the cutaway portions 7 thereby
adjusting the amount of coupling with an external circuit.
[0091] FIG. 23 is a cross-sectional view illustrating a method of
adjusting the characteristics of a dielectric waveguide filter
according to a 21st embodiment of the invention. In this filter
structure, as in the structure shown in FIG. 18, two through-holes
5 are formed in a dielectric block so that the through-holes 5
extend in a direction parallel to a shorter axis of the dielectric
block, and a coupling electrode 4 is formed on the inner surface of
each through-hole 5 wherein one end of each coupling electrode 4 is
connected to a corresponding terminal electrode 3 formed on the
outer surface of the dielectric block 1 and the other end of each
coupling electrode 4 is connected to a conducting film 2 formed on
the outer surface of the dielectric block 1. In this specific
example, a cutaway portion 7 is formed by cutting the upper portion
of the through-hole 5 thereby partially removing the coupling
electrode 4 together with a part of the dielectric block 1. Since
the one end of each coupling electrode still remains connected to
the conducting film 2, a coupling loop is formed by the coupling
electrodes 4 and the conducting film. However, the partial removal
of the coupling electrode 4 causes a change in the shape of the
coupling electrode 4, which in turn causes a change in the amount
of electrical coupling to a resonance mode via the coupling
electrode 4. Thus, it is possible to adjust the amount of coupling
by controlling the shape and amount of the cutaway portion 7.
[0092] In addition to the above-described structures of dielectric
waveguide filters and the methods of adjusting the characteristics
thereof, further structures and methods are also possible. For
example, in the structure shown in FIGS. 19A-19B, L-shaped probes
may be formed by cutting the open end portions of the coupling
electrodes 4 (the portions connected to the conducting film) in
such a manner as to partially remove the open end portions or inner
portions of the coupling electrodes 4. Similarly, in the structure
shown in FIGS. 22A-22B, L-shaped probes may be formed by partially
removing the open end portions or inner portions of the coupling
electrodes 4. Since the amount of electromagnetic coupling to a
resonance mode varies with the removal amount, it is possible to
adjust the amount of coupling to an external circuit.
[0093] Although the TE101 resonance mode is used in the specific
examples described above, the above-described methods and
structures may also be employed when filters are operated in
higher-order resonance modes.
[0094] Now referring to FIGS. 24-30, some structures to realize a
dielectric waveguide filter consisting of a plurality of resonator
stages will be described below.
[0095] FIG. 24 is a perspective view of a dielectric waveguide
filter according to a 22nd embodiment of the invention wherein a
cross section thereof is shown in FIG. 25. As shown in these
figures, the dielectric waveguide filter is constructed of a
dielectric block in the form of a generally rectangular prism whose
outer surface is covered with a conducting film 2. In the middle of
the dielectric block 1 in the longitudinal direction, there are
slots 20 serving as a node by which the dielectric block 1 is
divided into a plurality of sections along the longitudinal
direction. The inner surface of each slot 20 is covered with the
conducting film 2. Each section separated by the slots 20 serves as
a resonator. A through-hole 12a or 12b is formed in each resonator
section in such a manner that the through-hole extends through the
dielectric block in a direction along the shortest axis. No
conducting film is formed on the inner surface of the through-holes
12a and 12b. Terminal electrodes 3a and 3b are formed on end faces
of the dielectric block. Through-holes 5a and 5b are formed in the
dielectric block in such a manner that they extend from the
corresponding terminal electrodes 3a and 3b on the end faces of the
dielectric block 1 to the conducting film on the bottom face of the
dielectric block 1. Furthermore, a coupling electrode 4a or 4b is
formed on the inner surface of each through-hole 5a and 5b. This
structure serves as a two-stage band-pass dielectric waveguide
filter wherein the two terminal electrodes 3a and 3b act as input
and output terminals, respectively. The characteristics of the
filter are determined by the resonance frequencies of the two
resonator stages wherein the resonance frequencies are determined
by the inner diameters of the through-holes 12a and 12b. The size
and location of each through-hole 12a and 12b may be determined at
the stage of design, or the inner surfaces of the through-holes 12a
and 12b may be partially removed by proper amounts at the stage of
adjustment.
[0096] FIG. 26 is a perspective view of a dielectric waveguide
filter according to a 23rd embodiment of the invention wherein its
cross section is shown in FIG. 27. This dielectric waveguide filter
has an input/output structure different from that shown in FIGS. 24
and 25. In this embodiment, through-holes 5a and 5b are formed in a
dielectric block 1 in such a manner that they extend along the
shortest axis, and coupling electrodes 4a and 4b are formed on the
inner surfaces of the respective through-holes 5a and 5b wherein
one end of each coupling electrode 4a and 4b is electrically
open-circuited inside the through-hole 5a or 5b. In this structure,
the through-holes 5a and 5b, on the inner surfaces of which the
coupling electrodes are formed, extend in the same direction as the
direction of the through-holes 12a and 12b for adjusting the
resonance frequency. This allows simplification in the structure of
a mold used to form the dielectric block.
[0097] FIG. 28 is a cross-sectional view of a dielectric waveguide
filter according to a 24th embodiment of the invention. As shown in
the figure, the dielectric waveguide filter includes a substrate 13
of an insulating material. Thus, this filter consists of two major
sections: a dielectric block section and an insulating substrate
section. The dielectric block section is similar to that shown in
FIGS. 26 and 27 except that no coupling electrodes 4a and 4b are
provided. Pin-shaped conductors 11a and 11b project from the
insulating substrate 13. The dielectric block section and the
insulating substrate are combined together in such a manner that
the pin-shaped conductors 11a and 11b are inserted into
through-holes 5a and 5b formed in the dielectric block.
Input/output electrodes 18a and 18b are formed on the insulating
substrate 13 in such a manner that they are electrically connected
to the respective pin-shaped conductors 11a and 11b thereby making
connections to an external circuit.
[0098] FIG. 29 is a cross-sectional view of a dielectric waveguide
filter according to a 25th embodiment of the invention. In this
embodiment, the filter includes a dielectric block 1 having similar
structure to that shown in FIGS. 26 and 27 except that no coupling
electrodes 4a and 4b are provided. The filter also includes
pin-shaped conductors 11a and 11b which are inserted together with
insulators 19a and 19b made of a material such as synthetic resin
into through-holes 5a and 5b. These pin-shaped conductors 11a and
11b are electrically isolated by the insulators 19a and 19b. The
dielectric waveguide filter is electrically connected to an
external circuit via these pin-shaped conductors 11a and 11b.
[0099] FIG. 30 is a perspective view of a dielectric waveguide
filter according to a 26th embodiment of the invention. In this
embodiment, the dielectric waveguide filter serves as an antenna
duplexer including a transmission filter and a reception filter
formed in an integral fashion wherein the transmission and
reception filters each consist of three resonator stages. As shown
in FIG. 30, the dielectric waveguide filter includes a dielectric
block in the form of a generally rectangular prism whose outer
surface is covered with a conducting film 2. Slots 20 are formed on
longer sides of the dielectric block so that the dielectric blocks
are divided by these slots into a plurality of sections along the
longitudinal direction. The inner surfaces of these slots 20 are
covered with the conducting film 2. Each section separated by the
slots 20 acts as a resonator. A through-hole 12a, 12b, 12c, 12d,
12e, or 12f is formed in each resonator section in such a manner
that each through-hole extends through the dielectric block in a
direction along the shortest axis. No conducting film is formed on
the inner surface of the through-holes 12a-12f. Coupling electrode
through-holes 5a, 5c, and 5b are formed in two resonator sections
located at either end and in the central resonator, respectively.
As in the structure shown in FIG. 27, a coupling electrode is
formed on the inner surface of each through-hole. The coupling
electrode formed on the inner surface of the through-hole 5a is
connected to a transmitting circuit, the coupling electrode formed
on the inner surface of the through-hole 5c is connected to a
receiving circuit, and the coupling electrode formed on the inner
surface of the through-hole 5b is connected to an antenna. In this
structure, the resonance frequencies of three resonator stages
forming the transmission filter are determined by the through-holes
12a, 12b, and 12c, and the resonance frequencies of three resonator
stages forming the reception filter are determined by the
through-holes 12d, 12e, and 12f. The desired characteristics of the
transmission and reception filters can be obtained by properly
determining the size and location of each through-hole 12a-12f at
the stage of design, or by partially removing the inner surfaces of
the through-holes 12a-12f at the stage of adjustment.
[0100] The present invention has various advantages as described
below.
[0101] According to an aspect of the invention, it is possible to
adjust the resonance frequency by properly selecting the size
and/or location of the through-hole or recess while keeping the
outside dimensions of the dielectric block constant. Thus, it is
possible to set the resonance frequency and unloaded Q to desired
values over wide ranges by properly designing the outside
dimensions of the dielectric block and the size or location of the
through-hole or recess. This makes it possible to design the
unloaded Q in a more flexible fashion.
[0102] According to another aspect of the invention, it is possible
to produce a relatively great change in the resonance frequency by
forming a small through-hole or recess. This technique also makes
it possible to design the unloaded Q within an expanded range.
[0103] According to still another aspect of the invention, it is
possible to selectively adjust only the resonance frequency in the
second resonance mode relative to the resonance frequency in the
first resonance mode even in the case where the resonance
frequencies in the first and second resonance modes are close to
each other. Thus, this technique makes it easy to adjust the
difference in resonance frequency between two resonance modes.
[0104] According to a further aspect of the invention, the
resonance frequencies in the first and second resonance modes are
equally affected by the through-hole or recess and thus it is
possible to simultaneously set the resonance frequencies in the two
resonance modes to desired values simply by adjusting the single
through-hole or recess.
[0105] According to another aspect of the invention, it is possible
to easily set the resonance frequencies in two resonance modes such
that they are equal to each other or they are close to each
other.
[0106] According to still another aspect of the invention, the
through-hole or recess is formed so that the formation of the
through-hole or recess results in an enhanced perturbation effects
on the electric field.
[0107] According to a further aspect of the invention, the
through-hole or recess is formed in such a fashion that coarse and
fine adjustments of the resonance frequency can be easily
performed.
[0108] According to another aspect of the invention, a dielectric
material having a dielectric constant different from that of the
dielectric block is disposed in the through-hole or recess. This
allows a reduction in size and also allows an improvement in the
frequency-temperature characteristic.
[0109] According to still another aspect of the invention, the
opening end of the through-hole or recess is covered with a
conductor thereby ensuring that leakage of electromagnetic waves
toward the outside or unwanted electromagnetic coupling with an
external circuit can be prevented.
[0110] According to still another aspect of the invention, the
connection to an external circuit can be achieved without having to
insert an additional special member such as a probe into the hole
from the outside. Furthermore, this structure provides excellent
coupling to the external circuit without producing leakage of
electromagnetic waves toward the outside.
[0111] According to another aspect of the invention, it is possible
to form a coupling electrode in a flexible fashion in the
dielectric block.
[0112] According to still another aspect of the invention, coupling
to an external circuit can be achieved simply by inserting a
pin-shaped conductor serving as a coupling member into the
dielectric block. This technique allows a simplification of the
overall structure of the dielectric waveguide filter.
[0113] According to still another aspect of the invention, it is
possible to easily adjust the amount of coupling to an external
circuit simply by partially removing the coupling electrode without
having to use an additional special adjustment member and without
producing leakage of electromagnetic waves toward the outside.
[0114] According to a further aspect of the invention, it is
possible to adjust the amount of coupling to the external circuit
simply by partially removing the coupling electrode formed on the
inner surface of a hole formed in the dielectric block. This
technique allows a great degree of simplification of the adjustment
process.
[0115] According to a further aspect of the invention, the
resonance frequency can be adjusted simply by partially removing
the inner surface of the through-hole or recess. Thus, this
technique allows a great degree of simplification of the adjustment
process.
[0116] Although the invention has been illustrated in connection
with embodiments thereof, the invention is not limited to those
embodiments, but extends to all modifications and variations within
the fair spirit and scope of the invention.
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