U.S. patent application number 14/587097 was filed with the patent office on 2015-04-30 for high-frequency signal transmission line and electronic device.
The applicant listed for this patent is Murata Manufacturing Co., Ltd.. Invention is credited to Bunta OKAMOTO, Yuki WAKABAYASHI, Kuniaki YOSUI.
Application Number | 20150116060 14/587097 |
Document ID | / |
Family ID | 51353993 |
Filed Date | 2015-04-30 |
United States Patent
Application |
20150116060 |
Kind Code |
A1 |
YOSUI; Kuniaki ; et
al. |
April 30, 2015 |
HIGH-FREQUENCY SIGNAL TRANSMISSION LINE AND ELECTRONIC DEVICE
Abstract
A high-frequency signal transmission line includes a
plate-shaped dielectric element assembly, a linear signal line, and
a first ground conductor. The linear signal line is provided at the
dielectric element assembly and includes a plurality of thick
portions and a plurality of thin portions with a smaller width than
the thick portions. The first ground conductor is provided at the
dielectric element assembly and positioned on one side in a normal
direction to the dielectric element assembly relative to the signal
line. The first ground conductor includes a plurality of openings
overlapping with the signal line and also includes bridge portions
provided between the openings so as to cross the thin portions. The
bridge portions cross the thin portion obliquely when viewed in a
plan view in the normal direction to the dielectric element
assembly.
Inventors: |
YOSUI; Kuniaki;
(Nagaokakyo-shi, JP) ; WAKABAYASHI; Yuki;
(Nagaokakyo-shi, JP) ; OKAMOTO; Bunta;
(Nagaokakyo-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Murata Manufacturing Co., Ltd. |
Nagaokakyo-shi |
|
JP |
|
|
Family ID: |
51353993 |
Appl. No.: |
14/587097 |
Filed: |
December 31, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2014/052739 |
Feb 6, 2014 |
|
|
|
14587097 |
|
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Current U.S.
Class: |
333/238 |
Current CPC
Class: |
H01P 1/20363 20130101;
H01P 3/08 20130101; H03H 7/38 20130101; H01P 3/085 20130101; H05K
1/0225 20130101; H05K 2201/09618 20130101; H01P 3/081 20130101;
H01P 5/028 20130101; H05K 2201/09727 20130101; H05K 2201/09272
20130101; H05K 1/0253 20130101 |
Class at
Publication: |
333/238 |
International
Class: |
H01P 3/08 20060101
H01P003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2013 |
JP |
2013-025637 |
Jul 26, 2013 |
JP |
2013-155453 |
Claims
1. A high-frequency signal transmission line, comprising: a
plate-shaped dielectric element assembly; a signal line provided at
the dielectric element assembly and including a plurality of thick
portions and a plurality of thin portions with a smaller width than
the thick portions; and a first ground conductor provided at the
dielectric element assembly and positioned on one side in a normal
direction to the dielectric element assembly relative to the signal
line, the first ground conductor including a plurality of openings
overlapping with the signal line and also including bridge portions
provided between the openings so as to cross the thin portions;
wherein the bridge portions cross the thin portion obliquely when
viewed in a plan view in the normal direction to the dielectric
element assembly.
2. The high-frequency signal transmission line according to claim
1, wherein the thick portions overlap with the openings.
3. The high-frequency signal transmission line according to claim
1, further comprising a second ground conductor provided at the
dielectric element assembly on the other side in the normal
direction relative to the signal line so as to overlap with the
signal line.
4. The high-frequency signal transmission line according to claim
3, wherein the second ground conductor is provided with no openings
overlapping with the signal line.
5. The high-frequency signal transmission line according to claim
1, wherein the signal line is a linear signal line defined by a
linear conductor.
6. The high-frequency signal line according to claim 1, wherein the
plurality of openings is in a shape of one of a rectangle, a
parallelogram, and a trapezoid.
7. The high-frequency signal transmission line according to claim
1, wherein the openings and the bridge portions overlap with the
signal line alternatingly when seen in the plan view.
8. The high-frequency signal transmission line according to claim
3, wherein an overlap amount of the first ground conductor and the
signal line is different from an overlap amount of the second
ground conductor and the signal line.
9. An electronic device, comprising: a high-frequency signal
transmission line; and a housing accommodating the high-frequency
signal transmission line; wherein the high-frequency signal
transmission line includes: a plate-shaped dielectric element
assembly; a linear signal line provided at the dielectric element
assembly and including a plurality of thick portions and a
plurality of thin portions with a smaller width than the thick
portions; and a first ground conductor provided at the dielectric
element assembly and positioned on one side in a normal direction
to the dielectric element assembly relative to the signal line, the
first ground conductor including a plurality of openings
overlapping with the signal line and also including bridge portions
provided between the openings so as to cross the thin portions; and
the bridge portions cross the thin portion obliquely when viewed in
a plan view in the normal direction to the dielectric element
assembly.
10. The electronic device according to claim 9, wherein the thick
portions overlap with the openings.
11. The electronic device according to claim 9, further comprising
a second ground conductor provided at the dielectric element
assembly on the other side in the normal direction relative to the
signal line so as to overlap with the signal line.
12. The electronic device according to claim 11, wherein the second
ground conductor is provided with no openings overlapping with the
signal line.
13. The electronic device according to claim 9, wherein the signal
line is a linear signal line defined by a linear conductor.
14. The electronic device according to claim 9, wherein the
plurality of openings is in a shape of one of a rectangle, a
parallelogram, and a trapezoid.
15. The electronic device according to claim 9, wherein the
openings and the bridge portions overlap with the signal line
alternatingly when seen in the plan view.
16. The electronic device according to claim 11, wherein an overlap
amount of the first ground conductor and the signal line is
different from an overlap amount of the second ground conductor and
the signal line.
17. An electronic component comprising: first and second
high-frequency circuits; and the high-frequency signal line
according to claim 1; wherein the first and second high-frequency
circuits are connected to each other by the high-frequency signal
line.
18. The electronic component according to claim 17, wherein the
electric component is a cell phone.
Description
[0001] This application is based on Japanese Patent Application No.
2013-155453 filed on Jul. 26, 2013, Japanese Patent Application No.
2013-25637 filed on Feb. 13, 2013, and International Application
No. PCT/JP2014/52739 filed on Feb. 6, 2014, the entire contents of
each of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to high-frequency signal
transmission lines and electronic devices, more particularly to a
high-frequency signal transmission line preferably for use in
high-frequency signal transmission and an electronic device
including the same.
[0004] 2. Description of the Related Art
[0005] As an invention relevant to a conventional high-frequency
signal transmission line, a high-frequency signal line described
in, for example, International Patent Publication WO2012/073591
(see FIG. 12) is known.
[0006] The high-frequency signal line described in International
Patent Publication WO2012/073591 includes a dielectric element
assembly, a signal line, and first and second ground conductors.
The dielectric element assembly is formed by laminating a plurality
of dielectric sheets. The signal line is provided in the dielectric
element assembly. The first and second ground conductors are
provided in the dielectric element assembly so as to sandwich the
signal line in the direction of lamination. As a result, the signal
line and the first and second ground conductors form a stripline
structure.
[0007] Furthermore, in the high-frequency signal line described in
International Patent Publication WO2012/073591, the second ground
conductor has a plurality of openings arranged along the signal
line. That is, the second ground conductor has a ladder-shaped
configuration. Accordingly, little capacitance is created between
the signal line and the second ground conductor with the openings,
and therefore, it is possible to position the second ground
conductor and the signal line close to each other without
excessively increasing the capacitance generated between the second
ground conductor and the signal line. Thus, the high-frequency
signal line described in International Patent Publication
WO2012/073591 can be reduced in thickness without causing the
characteristic impedance of the signal line to change significantly
from a predetermined impedance value.
[0008] Incidentally, in the high-frequency signal line described in
International Patent Publication WO2012/073591, for the reasons as
will be described below, the second ground conductor has bridge
portions provided between adjacent openings so as to cross the
signal line. The high-frequency signal line is electrically
connected at opposite ends to circuit boards by, for example,
solder or connectors. Accordingly, the characteristic impedance of
the signal line is likely to vary at opposite ends compared to
other portions of the signal line. Therefore, high-frequency signal
reflection occurs between the opposite ends of the signal line, so
that noise with a half wavelength that is equal to the length of
the signal line occurs. The frequency of noise with such a long
wavelength tends to overlap with the effective bandwidth of an
electronic device in which the high-frequency signal line is
used.
[0009] Therefore, the high-frequency signal line described in
International Patent Publication WO2012/073591 has the bridge
portions overlapping with the signal line. The characteristic
impedance of the signal line is lower in the areas where the signal
line overlaps with the bridge portions than in the areas where the
signal line does not overlap with the bridge portions. Accordingly,
high-frequency signal reflection occurs at the overlapping portions
of the signal line and the bridge portions, so that noise with a
half wavelength that is equal to the distance between two adjacent
bridge portions occurs. The frequency of noise including such a
short wavelength is less likely to overlap with the effective
frequency of an electronic device in which the high-frequency
signal line is used.
[0010] However, in the high-frequency signal line described in
International Patent Publication WO2012/073591, high-frequency
signal reflection occurs at the overlapping portions of the signal
line and the bridge portions, resulting in increased insertion loss
in the high-frequency signal line.
[0011] Therefore, in the high-frequency signal line described in
International Patent Publication WO2012/073591, the width of the
signal line is narrower in the areas where the signal line overlaps
with the bridge portions than in the areas where the signal line
does not overlap with the bridge portions. This reduces the
capacitance generated between the signal line and the bridge
portions, so that the characteristic impedance of the signal line
is prevented from becoming excessively low at the overlapping
portions of the signal line and the bridge portions. That is,
high-frequency signal reflection at the overlapping portions of the
signal line and the bridge portions is reduced.
[0012] However, in the high-frequency signal line described in
International Patent Publication WO2012/073591, since the width of
the signal line narrows at the overlapping portions with the bridge
portions, the resistance of the signal line becomes high at such
overlapping portions. As a result, insertion loss in the
high-frequency signal line increases.
SUMMARY OF THE INVENTION
[0013] A preferred embodiment of the present invention is directed
to a high-frequency signal transmission line including a
plate-shaped dielectric element assembly, a linear signal line
provided at the dielectric element assembly and including a
plurality of thick portions and a plurality of thin portions with a
smaller width than the thick portions, and a first ground conductor
provided at the dielectric element assembly and positioned on one
side in a normal direction to the dielectric element assembly
relative to the signal line, the first ground conductor including a
plurality of openings overlapping with the signal line and also
including bridge portions provided between the openings so as to
cross the thin portions. The bridge portion crosses the thin
portion obliquely when viewed in a plan view in the normal
direction to the dielectric element assembly.
[0014] Another preferred embodiment of the present invention is
directed to an electronic device including a high-frequency signal
transmission line and a housing accommodating the high-frequency
signal transmission line. The high-frequency signal transmission
line includes a plate-shaped dielectric element assembly, a linear
signal line provided at the dielectric element assembly and
including a plurality of thick portions and a plurality of thin
portions with a smaller width than the thick portions, and a first
ground conductor provided at the dielectric element assembly and
positioned on one side in a normal direction to the dielectric
element assembly relative to the signal line, the first ground
conductor including a plurality of openings arranged so as to
overlap with the signal line and also including bridge portions
provided between the openings so as to cross the thin portions. The
bridge portion crosses the thin portion obliquely when viewed in a
plan view in the normal direction to the dielectric element
assembly.
[0015] The above and other elements, features, steps,
characteristics and advantages of the present invention will become
more apparent from the following detailed description of the
preferred embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an external oblique view of a high-frequency
signal transmission line according to a preferred embodiment of the
present invention.
[0017] FIG. 2 is an exploded view of a dielectric element assembly
of the high-frequency signal transmission line in FIG. 1.
[0018] FIG. 3 provides a diagram illustrating the high-frequency
signal transmission line with a signal line and an auxiliary ground
conductor overlapping with each other, and also provides a graph
showing a change in characteristic impedance of the signal
line.
[0019] FIG. 4 is a cross-sectional structure view of the
high-frequency signal transmission line taken along line A-A of
FIG. 2.
[0020] FIG. 5 is a cross-sectional structure view of the
high-frequency signal transmission line taken along line B-B of
FIG. 2.
[0021] FIG. 6 is an external oblique view of a connector of the
high-frequency signal transmission line.
[0022] FIG. 7 is a cross-sectional structure view of the
connector.
[0023] FIG. 8 illustrates an electronic device provided with a
high-frequency signal transmission line as viewed in a plan view in
the y-axis direction.
[0024] FIG. 9 illustrates the electronic device provided with the
high-frequency signal transmission line as viewed in a plan view in
the z-axis direction.
[0025] FIG. 10 provides a diagram illustrating a high-frequency
signal transmission line according to a comparative example with a
signal line and an auxiliary ground conductor overlapping with each
other, and also provides a graph showing a change in characteristic
impedance of the signal line.
[0026] FIG. 11 is an enlarged view of a thin portion and a bridge
portion in the high-frequency signal transmission line where cos
.theta.=W2/W1.
[0027] FIG. 12 is a view illustrating a high-frequency signal
transmission line according to a first modification of a preferred
embodiment of the present invention with a signal line and an
auxiliary ground conductor overlapping with each other.
[0028] FIG. 13 is a view illustrating a high-frequency signal
transmission line according to a second modification of a preferred
embodiment of the present invention with a signal line and an
auxiliary ground conductor overlapping with each other.
[0029] FIG. 14 is a view illustrating a high-frequency signal
transmission line according to a third modification of a preferred
embodiment of the present invention with a signal line and an
auxiliary ground conductor overlapping with each other.
[0030] FIG. 15 is an exploded view of a dielectric element assembly
of a high-frequency signal transmission line according to a fourth
modification of a preferred embodiment of the present
invention.
[0031] FIG. 16 is a view illustrating the high-frequency signal
transmission line according to the fourth modification of a
preferred embodiment of the present invention with a signal line
and an auxiliary ground conductor overlapping with each other.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Hereinafter, high-frequency signal transmission lines
according to preferred embodiments of the present invention, along
with an electronic device including the same, will be described
with reference to the drawings.
[0033] The configurations of the high-frequency signal transmission
line according to preferred embodiments will be described below
with reference to the drawings. FIG. 1 is an external oblique view
of the high-frequency signal transmission line 10 according to a
preferred embodiment of the present invention. FIG. 2 is an
exploded view of a dielectric element assembly 12 of the
high-frequency signal transmission line 10 in FIG. 1. FIG. 3
provides a diagram illustrating the high-frequency signal
transmission line 10 with a signal line 20 and an auxiliary ground
conductor 24 overlapping with each other, and also provides a graph
showing a change in characteristic impedance of the signal line 20.
In the graph, the vertical axis represents the characteristic
impedance, and the horizontal axis (x-axis) corresponds to the
longitudinal direction of the high-frequency signal transmission
line 10. FIG. 4 is a cross-sectional structure view of the
high-frequency signal transmission line 10 taken along line A-A of
FIG. 2. FIG. 5 is a cross-sectional structure view of the
high-frequency signal transmission line 10 taken along line B-B of
FIG. 2. In the following, the direction of lamination of the
high-frequency signal transmission line 10 (a normal direction to
the dielectric element assembly 12) will be defined as a z-axis
direction. In addition, the longitudinal direction of the
high-frequency signal transmission line 10 will be defined as an
x-axis direction, and the direction perpendicular to the x-axis and
z-axis directions will be defined as a y-axis direction.
[0034] The high-frequency signal transmission line 10 is preferably
used in an electronic device such as a cell phone, in order to
connect two high-frequency circuits, for example. The
high-frequency signal transmission line 10 includes the dielectric
element assembly 12, external terminals 16a and 16b, the signal
line 20, a reference ground conductor 22, the auxiliary ground
conductor 24, via-hole conductors b1 to b4 and B1 to B6, and
connectors 100a and 100b, as shown in FIGS. 1 and 2.
[0035] The dielectric element assembly 12 is a flexible
plate-shaped member extending in the x-axis direction when viewed
in a plan view in the z-axis direction, as shown in FIG. 1, and
includes a line portion 12a and connecting portions 12b and 12c.
The dielectric element assembly 12 is a laminate preferably formed
by laminating a protective layer 14, dielectric sheets 18a to 18c,
and a protective layer 15 in this order, from the positive side to
the negative side in the z-axis direction, as shown in FIG. 2. In
the following, the principal surface of the dielectric element
assembly 12 that is located on the positive side in the z-axis
direction will be referred to as a top surface, and the principal
surface of the dielectric element assembly 12 that is located on
the negative side in the z-axis direction will be referred to as a
bottom surface.
[0036] The line portion 12a is preferably in the form of a strip
extending in the x-axis direction, as shown in FIG. 1. The
connecting portions 12b and 12c are preferably in the form of
rectangles connected to the ends of the line portion 12a on the
negative and positive sides, respectively, in the x-axis direction.
Each of the connecting portions 12b and 12c is wider than the line
portion 12a in the y-axis direction.
[0037] The dielectric sheets 18a to 18c, when viewed in a plan view
in the z-axis direction, extend in the x-axis direction and have
the same shape as the dielectric element assembly 12, as shown in
FIG. 2. The dielectric sheets 18a to 18c are preferably made of a
flexible thermoplastic resin such as polyimide or liquid crystal
polymer. Each of the dielectric sheets 18a to 18c preferably has a
thickness of, for example, about 20 .mu.m to about 300 .mu.m, in
the present preferred embodiment, about 100 .mu.m.
[0038] Furthermore, the dielectric sheet 18a includes a line
portion 18a-a and connecting portions 18a-b and 18a-c. The
dielectric sheet 18b includes a line portion 18b-a and connecting
portions 18b-b and 18b-c. The dielectric sheet 18c includes a line
portion 18c-a and connecting portions 18c-b and 18c-c. The line
portions 18a-a, 18b-a, and 18c-a constitute the line portion 12a.
The connecting portions 18a-b, 18b-b, and 18c-b constitute the
connecting portion 12b. The connecting portions 18a-c, 18b-c, and
18c-c constitute the connecting portion 12c.
[0039] The signal line 20 preferably is a linear conductor provided
for high-frequency signal transmission in the direction in which
the dielectric element assembly 12 extends, as shown in FIG. 2. In
the present preferred embodiment, the signal line 20 is provided on
the bottom surface of the dielectric sheet 18b. The signal line 20
extends along the line portion 18b-a in the x-axis direction. The
end of the signal line 20 that is located on the negative side in
the x-axis direction is positioned at or approximately at the
center of the connecting portion 18b-b. The end of the signal line
20 that is located on the positive side in the x-axis direction is
positioned at or approximately at the center of the connecting
portion 18b-c.
[0040] Furthermore, the signal line 20 includes a plurality of
thick portions 20a and a plurality of thin portions 20b. The thin
portion 20b has a smaller width than the thick portion 20a. The
thick portions 20a and the thin portions 20b alternate with each
other. The width of the thick portion 20a preferably is, for
example, from about 300 .mu.m to about 700 In the present preferred
embodiment, the thick portion 20a preferably is about 300-.mu.m
wide, for example. The width of the thin portion 20b preferably is,
for example, from about 30 .mu.m to about 200 In the present
preferred embodiment, the thin portion 20b preferably is about
100-.mu.m wide, for example.
[0041] The signal line 20 is made of a metal material including
silver or copper and having a low specific resistance. Here, the
signal line 20 is formed on the bottom surface of the dielectric
sheet 18b preferably by patterning metal foil formed by plating the
bottom surface of the dielectric sheet 18b or preferably by
patterning metal foil attached to the bottom surface of the
dielectric sheet 18b. Moreover, the top surface of the signal line
20 is smoothened, so that surface roughness of the signal line 20
is greater on the side that contacts the dielectric sheet 18b than
on the side that does not contact the dielectric sheet 18b.
[0042] The reference ground conductor 22 is provided on the
positive side in the z-axis direction relative to the signal line
20. More specifically, the reference ground conductor 22 is
arranged on the top surface of the dielectric sheet 18a so as to be
opposite to the signal line 20 with the dielectric sheets 18a and
18b positioned therebetween. The characteristic impedance of the
high-frequency signal transmission line 10 is mainly determined by
the opposing areas of the signal line 20 and the reference ground
conductor 22 and the distance therebetween, as well as by the
relative permittivities of the dielectric sheets 18a to 18c.
Therefore, in the case where the characteristic impedance of the
high-frequency signal transmission line 10 is to be set to about
50.OMEGA., for example, the characteristic impedance of the
high-frequency signal transmission line 10 is designed to become
about 55.OMEGA., for example, slightly higher than about 50.OMEGA.,
because of the influence of the signal line 20 and the reference
ground conductor 22. Moreover, the auxiliary ground conductor 24 is
shaped as will be described later, such that the characteristic
impedance of the high-frequency signal transmission line 10 becomes
about 50.OMEGA. because of the influence of the signal line 20, the
reference ground conductor 22, and the auxiliary ground conductor
24.
[0043] The reference ground conductor 22 preferably is made of a
metal material including silver or copper and including a low
specific resistance. Here, the reference ground conductor 22 is
formed on the top surface of the dielectric sheet 18a preferably by
patterning metal foil formed by plating the top surface of the
dielectric sheet 18a or preferably by patterning metal foil
attached to the top surface of the dielectric sheet 18a. Moreover,
the top surface of the reference ground conductor 22 is smoothened,
so that surface roughness of the reference ground conductor 22 is
greater on the side that contacts the dielectric sheet 18a than on
the side that does not contact the dielectric sheet 18a.
[0044] Furthermore, the reference ground conductor 22 includes a
main conductor 22a and terminal conductors 22b and 22c. The main
conductor 22a is a strip-shaped conductor provided on the top
surface of the line portion 18a-a and extending in the x-axis
direction. The main conductor 22a is a solid conductor provided
with no openings overlapping with the signal line 20. The terminal
conductor 22b is preferably provided in the form of a rectangular
or substantially rectangular frame on the top surface of the
connecting portion 18a-b. The terminal conductor 22b is connected
to the end of the main conductor 22a on the negative side in the
x-axis direction. The terminal conductor 22c is preferably provided
in the form of a rectangular or substantially rectangular frame on
the top surface of the connecting portion 18a-c. The terminal
conductor 22c is connected to the end of the main conductor 22a on
the positive side in the x-axis direction.
[0045] The auxiliary ground conductor 24 is positioned on the
negative side in the z-axis direction relative to the signal line
20. The auxiliary ground conductor 24 preferably includes a
plurality of openings 30 arranged along the signal line 20. More
specifically, the auxiliary ground conductor 24 is arranged on the
bottom surface of the dielectric sheet 18c, so as to be opposite to
the signal line 20 with the dielectric sheet 18c positioned
therebetween. The auxiliary ground conductor 24 is a ground
conductor that doubles as a shield.
[0046] The auxiliary ground conductor 24 is made of a metal
material including silver or copper and including a low specific
resistance. Here, the auxiliary ground conductor 24 is formed on
the bottom surface of the dielectric sheet 18c preferably by
patterning metal foil formed by plating the bottom surface of the
dielectric sheet 18c or preferably by patterning metal foil
attached to the bottom surface of the dielectric sheet 18c.
Moreover, the top surface of the auxiliary ground conductor 24 is
smoothened, so that surface roughness of the auxiliary ground
conductor 24 is greater on the side that contacts the dielectric
sheet 18c than on the side that does not contact the dielectric
sheet 18c.
[0047] Furthermore, the auxiliary ground conductor 24 includes a
main conductor 24a and terminal conductors 24b and 24c. The main
conductor 24a is a strip-shaped conductor provided on the bottom
surface of the line portion 18c-a and extending in the x-axis
direction. The main conductor 24a preferably includes the openings
30 provided therein, as shown in FIG. 2. Accordingly, the main
conductor 24a preferably has a ladder-shaped configuration. The
openings 30 overlap with the thick portions 20a when viewed in a
plan view in the z-axis direction, as shown in FIG. 3. In the
present preferred embodiment, the thick portions 20a are positioned
within the openings 30 when viewed in a plan view in the z-axis
direction.
[0048] Furthermore, since the openings 30 are provided, the main
conductor 24a preferably includes a plurality of bridge portions 60
between adjacent openings 30. The bridge portions 60 extend
essentially in the y-axis direction so as to cross the thin
portions 20b, when viewed in a plan view in the z-axis direction,
as shown in FIG. 3. The bridge portions 60 are oblique toward the
positive end in the x-axis direction when viewed from the center
toward the positive end in the y-axis direction. Accordingly, the
bridge portions 60 cross the thin portions 20b obliquely when
viewed in a plan view in the z-axis direction. Note that the
oblique crossing means that the bridge portion 60 is neither
parallel nor perpendicular to the thin portion 20b, and makes an
angle greater than 0.degree. but less than 90.degree. with respect
to the thin portion 20b. Moreover, the bridge portion 60 extends
straight in the y-axis direction at opposite ends.
[0049] In the main conductor 24a, the openings 30 and the bridge
portions 60 overlap with the signal line 20 alternatingly when
viewed in a plan view in the z-axis direction. Moreover, in the
present preferred embodiment, the signal line 20 crosses the
openings 30 and the bridge portions 60 in the x-axis direction so
as to pass through their approximate centers in the y-axis
direction.
[0050] The terminal conductor 24b is preferably provided in the
form of a rectangular or substantially rectangular frame on the
bottom surface of the connecting portion 18c-b. The terminal
conductor 24b is connected to the end of the main conductor 24a on
the negative side in the x-axis direction. The terminal conductor
24c is preferably provided in the form of a rectangular or
substantially rectangular frame on the bottom surface of the
connecting portion 18c-c. The terminal conductor 24c is connected
to the end of the main conductor 24a on the positive side in the
x-axis direction.
[0051] Furthermore, the auxiliary ground conductor 24 is designed
for final adjustments to the characteristic impedance of the
high-frequency signal transmission line 10 such that it becomes
about 50.OMEGA., as described earlier. In addition, the interval
between the bridge portions 60 of the auxiliary ground conductor 24
is designed so as not to cause noise to be generated within the
effective bandwidth. More specifically, the interval between
adjacent bridge portions 60 is preferably designed to be shorter
than a half of the wavelength of a frequency in the effective
bandwidth for the high-frequency signal transmission line 10 and an
electronic device using the high-frequency signal transmission line
10. As a result, the frequency of noise radiated from the signal
line 20 does not overlap with the effective bandwidth for the
high-frequency signal transmission line 10 and the electronic
device using the high-frequency signal transmission line 10.
[0052] The external terminal 16a preferably is a rectangular or
substantially rectangular conductor provided essentially at the
center on the top surface of the connecting portion 18a-b, as shown
in FIGS. 1 and 2. Accordingly, the external terminal 16a, when
viewed in a plan view in the z-axis direction, overlaps with the
end of the signal line 20 on the negative side in the x-axis
direction. The external terminal 16b preferably is a rectangular or
substantially rectangular conductor provided essentially at the
center on the top surface of the connecting portion 18a-c, as shown
in FIGS. 1 and 2. Accordingly, the external terminal 16b, when
viewed in a plan view in the z-axis direction, overlaps with the
end of the signal line 20 on the positive side in the x-axis
direction.
[0053] The external terminals 16a and 16b are preferably made of a
metal material including silver or copper and including a low
specific resistance. In addition, the top surfaces of the external
terminals 16a and 16b are preferably plated with Ni and Au. Here,
the external terminals 16a and 16b are formed on the top surface of
the dielectric sheet 18a preferably by patterning metal foil formed
by plating the top surface of the dielectric sheet 18a or
preferably by patterning metal foil attached to the top surface of
the dielectric sheet 18a. Moreover, the top surfaces of the
external terminals 16a and 16b are smoothened, so that surface
roughness of the external terminals 16a and 16b is greater on the
side that contacts the dielectric sheet 18a than on the side that
does not contact the dielectric sheet 18a.
[0054] In this manner, the signal line 20 is positioned between the
reference ground conductor 22 and the auxiliary ground conductor 24
in the z-axis direction. That is, the signal line 20, the reference
ground conductor 22, and the auxiliary ground conductor 24 define a
tri-plate stripline structure. However, the auxiliary ground
conductor 24 has the openings 30 provided therein, and therefore,
the area of the auxiliary ground conductor 24 that is opposite to
the signal line 20 is smaller than the area of the reference ground
conductor 22 that is opposite to the signal line 20, i.e., an
overlap amount of the auxiliary ground conductor 24 and the signal
line 20 is less than an overlap amount of the reference ground
conductor 22 and the signal line 20.
[0055] Moreover, the distance T1 between the signal line 20 and the
reference ground conductor 22 preferably is, for example, from
about 20 .mu.m to about 300 .mu.m, which is equal or approximately
equal to the total of the thickness of the dielectric sheet 18a and
the thickness of the dielectric sheet 18b, as shown in FIGS. 4 and
5. In the present preferred embodiment, the distance T1 between the
signal line 20 and the reference ground conductor 22 preferably is
about 100 .mu.m, for example. On the other hand, the distance T2
between the signal line 20 and the auxiliary ground conductor 24
preferably is, for example, from about 10 .mu.m to about 100 .mu.m,
which is equal or approximately equal to the thickness of the
dielectric sheet 18c, as shown in FIGS. 4 and 5. In the present
preferred embodiment, the distance T2 between the signal line 20
and the auxiliary ground conductor 24 preferably is about 50 .mu.m,
for example. That is, the distance T1 between the reference ground
conductor 22 and the signal line 20 is designed to be greater than
the distance T2 between the auxiliary ground conductor 24 and the
signal line 20.
[0056] The via-hole conductor b1 pierces through the connecting
portion 18a-b of the dielectric sheet 18a in the z-axis direction.
The via-hole conductor b2 pierces through the connecting portion
18b-b of the dielectric sheet 18b in the z-axis direction. The
via-hole conductors b1 and b2 are connected to each other to
constitute a single via-hole conductor, thus connecting the
external terminal 16a to the end of the signal line 20 that is
located on the negative side in the x-axis direction. The via-hole
conductor b3 pierces through the connecting portion 18a-c of the
dielectric sheet 18a in the z-axis direction. The via-hole
conductor b4 pierces through the connecting portion 18b-c of the
dielectric sheet 18b in the z-axis direction. The via-hole
conductors b3 and b4 are connected to each other to constitute a
single via-hole conductor, thus connecting the external terminal
16b to the end of the signal line 20 that is located on the
positive side in the x-axis direction. As a result, the signal line
20 is connected between the external terminals 16a and 16b. The
via-hole conductors b1 to b4 are preferably formed by filling
through-holes, which are provided in the dielectric sheets 18a and
18b, with a metal material.
[0057] The via-hole conductors B1 pierce through the line portion
18a-a of the dielectric sheet 18a in the z-axis direction. The
via-hole conductors B1 are positioned on the positive side in the
y-axis direction relative to the bridge portions 60 so as to be
arranged in a line in the x-axis direction, as shown in FIG. 2. The
via-hole conductors B2 pierce through the line portion 18b-a of the
dielectric sheet 18b in the z-axis direction. The via-hole
conductors B2 are positioned on the positive side in the y-axis
direction relative to the bridge portions 60 so as to be arranged
in a line in the x-axis direction, as shown in FIG. 2. The via-hole
conductors B3 pierce through the line portion 18c-a of the
dielectric sheet 18c in the z-axis direction. The via-hole
conductors B3 are positioned on the positive side in the y-axis
direction relative to the bridge portions 60 so as to be arranged
in a line in the x-axis direction, as shown in FIG. 2. The via-hole
conductors B1 to B3 are connected to one another such that each set
constitutes a single via-hole conductor, thus connecting the
reference ground conductor 22 and the auxiliary ground conductor
24. The via-hole conductors B1 to B3 are preferably formed by
filling through-holes, which are provided in the dielectric sheets
18a to 18c, with a metal material.
[0058] The via-hole conductors B4 pierce through the line portion
18a-a of the dielectric sheet 18a in the z-axis direction. The
via-hole conductors B4 are positioned on the negative side in the
y-axis direction relative to the bridge portions 60 so as to be
arranged in a line in the x-axis direction, as shown in FIG. 2. The
via-hole conductors B5 pierce through the line portion 18b-a of the
dielectric sheet 18b in the z-axis direction. The via-hole
conductors B5 are positioned on the negative side in the y-axis
direction relative to the bridge portions 60 so as to be arranged
in a line in the x-axis direction, as shown in FIG. 2. The via-hole
conductors B6 pierce through the line portion 18c-a of the
dielectric sheet 18c in the z-axis direction. The via-hole
conductors B6 are positioned on the negative side in the y-axis
direction relative to the bridge portions 60 so as to be arranged
in a line in the x-axis direction, as shown in FIG. 2. The via-hole
conductors B4 to B6 are connected to one another such that each set
constitutes a single via-hole conductor, thus connecting the
reference ground conductor 22 and the auxiliary ground conductor
24. The via-hole conductors B4 to B6 are preferably formed by
filling through-holes, which are provided in the dielectric sheets
18a to 18c, with a metal material.
[0059] The protective layer 14 is an insulating film covering
approximately the entire top surface of the dielectric sheet 18a.
Accordingly, the reference ground conductor 22 is covered by the
protective layer 14. The protective layer 14 is made of, for
example, a flexible resin such as a resist material.
[0060] Furthermore, the protective layer 14 includes a line portion
14a and connecting portions 14b and 14c, as shown in FIG. 2. The
line portion 14a covers the entire top surface of the line portion
18a-a, thus covering the main conductor 22a.
[0061] The connecting portion 14b is connected to the end of the
line portion 14a on the negative side in the x-axis direction, and
covers the top surface of the connecting portion 18b. However, the
connecting portion 14b including openings Ha to Hd provided
therein. The opening Ha preferably is a rectangular or
substantially rectangular opening provided at the center of the
connecting portion 14b. The external terminal 16a is exposed to the
outside from the opening Ha. The opening Hb preferably is a
rectangular or substantially rectangular opening positioned on the
positive side in the y-axis direction relative to the opening Ha.
The opening Hc preferably is a rectangular or substantially
rectangular opening positioned on the negative side in the x-axis
direction relative to the opening Ha. The opening Hd preferably is
a rectangular or substantially rectangular opening positioned on
the negative side in the y-axis direction relative to the opening
Ha. The terminal portion 22b is exposed to the outside from the
openings Hb to Hd, so that the exposed portions serve as external
terminals.
[0062] The connecting portion 14c is connected to the end of the
line portion 14a on the positive side in the x-axis direction, and
covers the top surface of the connecting portion 18a-c. However,
the connecting portion 14c includes openings He to Hh provided
therein. The opening He preferably is a rectangular or
substantially rectangular opening provided at the center of the
connecting portion 14c. The external terminal 16b is exposed to the
outside from the opening He. The opening Hf preferably is a
rectangular or substantially rectangular opening positioned on the
positive side in the y-axis direction relative to the opening He.
The opening Hg preferably is a rectangular or substantially
rectangular opening positioned on the positive side in the x-axis
direction relative to the opening He. The opening Hh preferably is
a rectangular or substantially rectangular opening positioned on
the negative side in the y-axis direction relative to the opening
He. The terminal conductor 22c is exposed to the outside from the
openings Hf to Hh, so that the exposed portions define and serve as
external terminals.
[0063] The protective layer 15 is an insulating film covering
approximately the entire bottom surface of the dielectric sheet
18c. Accordingly, the ground conductor 24 is covered by the
protective layer 15. The protective layer 15 is made of, for
example, a flexible resin such as a resist material.
[0064] In the high-frequency signal transmission line 10 thus
configured, the characteristic impedance of the signal line 20
fluctuates cyclically between impedance values Z1 and Z2, as shown
in the graph in FIG. 3. More specifically, at the overlapping
portions of the signal line 20 and the openings 30, relatively low
capacitance is generated between the signal line 20 and the
reference ground conductor 22 and also between the signal line and
the auxiliary ground conductor 24. Accordingly, the characteristic
impedance of the signal line 20 is relatively high at the impedance
value Z1 at the overlapping portions with the openings 30.
[0065] On the other hand, at the overlapping portions of the signal
line 20 and the bridge portions 60, relatively high capacitance is
generated between the signal line 20 and the reference ground
conductor 22 and also between the signal line 20 and the auxiliary
ground conductor 24. Accordingly, at the overlapping portions of
the signal line 20 and the bridge portions 60, the characteristic
impedance of the signal line 20 is relatively low at the impedance
value Z2. Moreover, the openings 30 and the bridge portions 60 are
arranged so as to alternate with each other in the x-axis
direction. Accordingly, the characteristic impedance of the signal
line 20 fluctuates cyclically between the impedance values Z1 and
Z2. The impedance value Z1 preferably is, for example, about
55.OMEGA., and the impedance value Z2 is, for example, about
45.OMEGA.. The average characteristic impedance of the entire
signal line 20 preferably is, for example, about 50.OMEGA..
[0066] The connectors 100a and 100b are mounted on the top surfaces
of the connecting portions 12b and 12c, respectively, as shown in
FIG. 1. The connectors 100a and 100b preferably have the same
configuration, and therefore, only the configuration of the
connector 100b will be described below as an example. FIG. 6 is an
external oblique view of the connector 100b of the high-frequency
signal transmission line 10. FIG. 7 is a cross-sectional structure
view of the connector 100b.
[0067] The connector 100b includes a connector body 102, external
terminals 104 and 106, a center conductor 108, and an external
conductor 110, as shown in FIGS. 1, 6, and 7. The connector body
102 preferably includes a rectangular or substantially rectangular
plate and a cylindrical or substantially cylindrical portion
coupled thereon, and is made of an insulating material such as
resin.
[0068] The external terminal 104 is positioned on the plate of the
connector body 102 on the negative side in the z-axis direction, so
as to face the external terminal 16b. The external terminal 106 is
positioned on the plate of the connector body 102 on the negative
side in the z-axis direction, so as to correspond to the portions
of the terminal portion 22c exposed from the openings Hf to Hh.
[0069] The center conductor 108 is positioned at the center of the
cylindrical portion of the connector body 102, and is connected to
the external terminal 104. The center conductor 108 is a signal
terminal to/from which a high-frequency signal is
inputted/outputted. The external conductor 110 is positioned on the
inner circumferential surface of the cylindrical portion of the
connector body 102, and is connected to the external terminal 106.
The external conductor 110 is a ground terminal to be kept at a
ground potential.
[0070] The connector 100b thus configured is mounted on the top
surface of the connecting portion 12c, such that the external
terminal 104 is connected to the external terminal 16b, and the
external terminal 106 is connected to the terminal portion 22c, as
shown in FIG. 6. As a result, the signal line 20 is electrically
connected to the center conductor 108. In addition, the reference
ground conductor 22 and the auxiliary ground conductor 24 are
electrically connected to the external conductor 110.
[0071] The high-frequency signal transmission line 10 is preferably
used in a manner as will be described below. FIG. 8 illustrates an
electronic device 200 provided with the high-frequency signal
transmission line 10 as viewed in a plan view in the y-axis
direction. FIG. 9 illustrates the electronic device 200 provided
with the high-frequency signal transmission line 10 as viewed in a
plan view in the z-axis direction.
[0072] The electronic device 200 includes the high-frequency signal
transmission line 10, circuit boards 202a and 202b, receptacles
204a and 204b, a battery pack (metallic body) 206, and a housing
210.
[0073] The housing 210 accommodates the high-frequency signal
transmission line 10, the circuit boards 202a and 202b, the
receptacles 204a and 204b, and the battery pack 206. The circuit
board 202a is provided with, for example, a transmission or
reception circuit including an antenna. The circuit board 202b is
provided with, for example, a feed circuit. The battery pack 206
is, for example, a lithium-ion secondary battery, and the surface
thereof is wrapped by a metal cover. The circuit board 202a, the
battery pack 206, and the circuit board 202b are arranged in this
order, from the negative side to the positive side in the x-axis
direction.
[0074] The receptacles 204a and 204b are provided on the principal
surfaces of the circuit boards 202a and 202b, respectively, on the
negative side in the z-axis direction. The receptacles 204a and
204b are connected to the connectors 100a and 100b, respectively.
Accordingly, high-frequency signals to be transmitted between the
circuit boards 202a and 202b at a frequency of, for example, 2 GHz
are applied to the center conductors 108 of the connectors 100a and
100b via the receptacles 204a and 204b, respectively. Moreover, the
external conductors 110 of the connectors 100a and 100b are kept at
a ground potential by the circuit boards 202a and 202b and the
receptacles 204a and 204b. Thus, the high-frequency signal
transmission line 10 connects the circuit boards 202a and 202b.
[0075] Here, the top surface of the dielectric element assembly 12
(more precisely, the protective layer 14) is in contact with the
battery pack 206. The dielectric element assembly 12 and the
battery pack 206 are fixed preferably by an adhesive or the like.
The top surface of the dielectric element assembly 12 is the
principal surface that is located on the side of the reference
ground conductor 22 relative to the signal line 20. Accordingly,
the reference ground conductor 22, which is preferably in the form
of a solid with no openings, is positioned between the signal line
20 and the battery pack 206.
[0076] A non-limiting example of a method for producing the
high-frequency signal transmission line 10 will be described below
with reference to the drawings. While the following description
focuses on one high-frequency signal transmission line 10 as an
example, in actuality, large-sized dielectric sheets are laminated
and cut, so that a plurality of high-frequency signal transmission
lines 10 are produced at the same time.
[0077] Prepared first are dielectric sheets 18a to 18c made of a
thermoplastic resin, each sheet including one of its principal
faces copper-foiled (i.e., coated with a metal film). More
specifically, copper foil is attached to the top surfaces of the
dielectric sheets 18a to 18c. In addition, the copper-foiled
surfaces of the dielectric sheets 18a to 18c are smoothened, for
example, by galvanization for rust prevention. The dielectric
sheets 18a to 18c are sheets of liquid crystal polymer. The
thickness of the copper foil is from about 10 .mu.m to about 20
.mu.m.
[0078] Next, external terminals 16a and 16b and a reference ground
conductor 22, as shown in FIG. 2, are formed on the top surface of
the dielectric sheet 18a preferably by patterning the copper foil
on the top surface of the dielectric sheet 18a. More specifically,
resists are printed on the copper foil of the dielectric sheet 18a
in the same shapes as the external terminals 16a and 16b and the
reference ground conductor 22 shown in FIG. 2. Then, any portions
of the copper foil that are not coated with the resists are removed
by etching the copper foil. Thereafter, the resists are removed by
spraying a resist solvent. In this manner, the external terminals
16a and 16b and the reference ground conductor 22, as shown in FIG.
2, are formed on the top surface of the dielectric sheet 18a by
photolithography.
[0079] Next, a signal line 20, as shown in FIG. 2, is formed on the
bottom surface of the dielectric sheet 18b. In addition, a ground
conductor 24, as shown in FIG. 2, is formed on the bottom surface
of the dielectric sheet 18c. The steps of forming the signal line
20 and the auxiliary ground conductor 24 are the same as the steps
of forming the external terminals 16a and 16b and the reference
ground conductor 22, and therefore, any detailed descriptions
thereof will be omitted.
[0080] Next, via-holes are bored through the dielectric sheets 18a
to 18c by irradiating the dielectric sheets 18a to 18c with laser
beams where via-hole conductors b1 to b4 and B1 to B6 are to be
formed. Thereafter, the via-holes are filled with a conductive
paste, thus forming the via-hole conductors b1 to b4 and B1 to
B6.
[0081] Next, the dielectric sheets 18a to 18c are stacked in this
order, from the positive side to the negative side in the z-axis
direction, thus obtaining a dielectric element assembly 12. The
dielectric element assembly 12 is heated and pressed from both the
positive and negative sides in the z-axis direction. As a result,
the dielectric sheets 18a to 18c are softened and fluidized.
Thereafter, the dielectric sheets 18a to 18c solidify as the
dielectric element assembly 12 cools down. Consequently, the
dielectric sheets 18a to 18c are fused so that the dielectric
element assembly 12 is completed.
[0082] Next, a resin (resist) paste is applied to the top surface
of the dielectric sheet 18a by screen printing, thus forming a
protective layer 14 on the top surface of the dielectric sheet 18a
so as to cover the reference ground conductor 22. In addition, a
resin (resist) paste is applied to the bottom surface of the
dielectric sheet 18c by screen printing, thus forming a protective
layer 15 on the bottom surface of the dielectric sheet 18c so as to
cover the auxiliary ground conductor 24.
[0083] Lastly, the connectors 100a and 100b are mounted on the
connecting portions 12b and 12c by soldering them to the external
terminals 16a and 16b and the terminal portions 22b and 22c, thus
obtaining a high-frequency signal transmission line 10, as shown in
FIG. 1.
[0084] The high-frequency signal transmission line 10 thus
configured renders it possible to reduce insertion loss. FIG. 10
provides a diagram illustrating a high-frequency signal
transmission line 510 according to a comparative example with a
signal line 520 and an auxiliary ground conductor 524 overlapping
with each other, and also provides a graph showing a change in
characteristic impedance of the signal line 520. In the graph, the
vertical axis represents the characteristic impedance, and the
horizontal axis (x-axis) corresponds to the longitudinal direction
of the high-frequency signal transmission line 510. Note that the
components of the high-frequency signal transmission line 510 that
correspond to those of the high-frequency signal transmission line
10 are denoted by adding 500 to the reference numerals for the
high-frequency signal transmission line 10.
[0085] The high-frequency signal transmission line 510 according to
the comparative example differs from the high-frequency signal
transmission line 10 in that bridge portions 560 cross thin
portions 520b perpendicularly or substantially perpendicularly.
Since the bridge portions 560 cross the thin portions 520b
perpendicularly, the extent of overlapping between the signal line
520 and the bridge portion 560 in the y-axis direction changes
sharply. Accordingly, capacitance generated between the signal line
520 and the bridge portion 560 also varies sharply. Therefore, the
characteristic impedance of the signal line 520 changes abruptly
between impedance values Z11 and Z12, as shown in FIG. 10. In the
high-frequency signal transmission line 510 as above,
high-frequency signal reflection occurs readily at the overlapping
portions of the signal line 520 and the bridge portions 560.
[0086] Therefore, in the high-frequency signal transmission line
10, the bridge portions 60, when viewed in a plan view in the
z-axis direction, cross the thin portions 20b obliquely.
Accordingly, the extent of overlapping between the signal line 20
and the bridge portion 60 in the y-axis direction increases
gradually and then decreases gradually, as shown in FIG. 3. As a
result, capacitance generated between the signal line 20 and the
bridge portion 60 also increases gradually and then decreases
gradually. Therefore, the characteristic impedance of the signal
line 20 changes gently between the impedance values Z1 and Z2, as
shown in FIG. 3. In the high-frequency signal transmission line 10
as above, high-frequency signal reflection is less likely to occur
at the overlapping portions of the signal line 20 and the bridge
portions 60. Thus, the high-frequency signal transmission line 10
renders it possible to reduce insertion loss.
[0087] Further, in the high-frequency signal transmission line 10,
high-frequency signal reflection in the thin portions 20b is
significantly reduced or prevented by designing the characteristic
impedance of the signal line 20 to fluctuate gently. Accordingly,
in the case where high-frequency signal reflection in the thin
portions 20b is reduced sufficiently or prevented, the width of the
thin portion 20b may be increased. This reduces the resistance of
the thin portion 20b, resulting in reduced insertion loss in the
high-frequency signal transmission line 10. In addition, increasing
the width of the thin portion 20b prevents the thin portion 20b
from being broken.
[0088] Incidentally, in the case where the thin portion 20b has a
width W1, the bridge portion 60 has a width W2, and the thin
portion 20b and the bridge portion 60 form an angle .theta., the
following formula (1) is preferably satisfied, as will be described
below.
cos .omega.>W2/W1 (1)
[0089] FIG. 11 is an enlarged view of the thin portion 20b and the
bridge portion 60 in the high-frequency signal transmission line 10
where cos .theta.=W2/W1. FIG. 11 shows an intersection P1 of the
outer edge of the bridge portion 60 that is located on the positive
side in the y-axis direction and the outer edge of the thin portion
20b that is located on the positive side in the y-axis direction,
as well as an intersection P2 of the outer edge of the bridge
portion 60 that is located on the negative side in the y-axis
direction and the outer edge of the thin portion 20b that is
located on the negative side in the y-axis direction, and the
intersections P1 and P2 are aligned in the y-axis direction.
Accordingly, the dimension of the overlap of the signal line 20 and
the bridge portion 60 in the y-axis direction is maximized between
the intersections P1 and P2 and is equal to the width W1. The
dimension of the overlap of the signal line 20 and the bridge
portion 60 in the y-axis direction decreases from the intersections
P1 and P2 toward the positive end in the x-axis direction. In this
case, the relationships represented by formulas (2) and (3) are
satisfied.
sin .theta.=W2/D (2)
tan .theta.=W1/D (3)
[0090] By rearranging formulas (2) and (3), formula (4) can be
obtained.
cos .theta.=W2/W1 (4)
[0091] In this case, if the angle .theta. between the thin portion
20b and the bridge portion 60 shown in FIG. 11 is decreased, the
maximum dimension of the overlap of the signal line 20 and the
bridge portion 60 in the y-axis direction becomes less than the
width W1. That is, by satisfying formula (1), the maximum dimension
of the overlap of the signal line 20 and the bridge portion 60 in
the y-axis direction is lowered. By decreasing the maximum
dimension of the overlap of the signal line 20 and the bridge
portion 60 in the y-axis direction in this manner, the capacitance
generated between the thin portion 20b and the bridge portion 60 is
reduced, so that the impedance value Z2 is set close to the
impedance value Z1. Thus, the occurrence of high-frequency signal
reflection at the overlapping portions of the signal line 20 and
the bridge portions 60 is reduced or prevented more
effectively.
[0092] Further, the high-frequency signal transmission line 10
renders it possible to prevent the bridge portions 60 from peeling
off the dielectric sheet 18c. More specifically, when the
high-frequency signal transmission line 510 shown in FIG. 10 is
bent, the bridge portions 560 become parallel or substantially
parallel to the bending line. In this case, if any bridge portion
560 is located along the bending line, the bridge portion 560 might
peel off the dielectric sheet. On the other hand, in the
high-frequency signal transmission line 10, the bridge portions 60
are oblique relative to the y-axis direction and therefore do not
become parallel or substantially parallel to the bending line.
Thus, even if any bridge portion 60 is located at the bending line,
the bridge portion 60 is prevented from peeling off the dielectric
sheet 18c.
[0093] Still further, in the high-frequency signal transmission
line 10, the reference ground conductor 22 has no openings provided
therein. This results in enhanced shielding effectiveness on the
top-face side of the high-frequency signal transmission line 10.
Accordingly, even if the top surface of the high-frequency signal
transmission line 10 is attached to or placed near a metallic body
such as the battery pack 206, capacitance is prevented from being
created between the signal line 20 and the battery pack 206. Thus,
the characteristic impedance of the high-frequency signal
transmission line 10 is prevented from fluctuating
significantly.
First Modification
[0094] Hereinafter, a high-frequency signal transmission line 10a
according to a first modification of a preferred embodiment of the
present invention will be described with reference to the drawings.
FIG. 12 is a view illustrating the high-frequency signal
transmission line 10a with the signal line 20 and the auxiliary
ground conductor 24 overlapping with each other. For the external
oblique view of the high-frequency signal transmission line 10a,
FIG. 1 will be referenced.
[0095] The high-frequency signal transmission line 10a differs from
the high-frequency signal transmission line 10 in the shape of the
bridge portion 60. More specifically, the bridge portion 60 of the
high-frequency signal transmission line 10a preferably is in the
form of a straight line which obliquely extends toward the positive
end in the x-axis direction when viewed in the direction toward the
positive end in the y-axis direction. Accordingly, the opening 30
preferably is in the shape of a parallelogram, for example.
[0096] As with the high-frequency signal transmission line 10, the
high-frequency signal transmission line 10a also renders it
possible to reduce insertion loss.
Second Modification
[0097] Hereinafter, a high-frequency signal transmission line 10b
according to a second modification of a preferred embodiment of the
present invention will be described with reference to the drawings.
FIG. 13 is a view illustrating the high-frequency signal
transmission line 10b with the signal line 20 and the auxiliary
ground conductor 24 overlapping with each other. For the external
oblique view of the high-frequency signal transmission line 10b,
FIG. 1 will be referenced.
[0098] The high-frequency signal transmission line 10b differs from
the high-frequency signal transmission line 10 in the shape of the
bridge portion 60. More specifically, the bridge portion 60 of the
high-frequency signal transmission line 10b preferably is in the
shape of a V that has been rotated 90 degrees clockwise. That is, a
half of the bridge portion 60 on the positive side in the y-axis
direction obliquely extends toward the positive end in the x-axis
direction when viewed in the direction toward the positive end in
the y-axis direction. The other half of the bridge portion 60 on
the negative side in the y-axis direction obliquely extends toward
the positive end in the x-axis direction when viewed in the
direction toward the negative end in the y-axis direction.
[0099] As with the high-frequency signal transmission line 10, the
high-frequency signal transmission line 10b as above also renders
it possible to reduce insertion loss.
Third Modification
[0100] Hereinafter, a high-frequency signal transmission line 10c
according to a third modification of a preferred embodiment of the
present invention will be described with reference to the drawings.
FIG. 14 is a view illustrating the high-frequency signal
transmission line 10c with the signal line 20 and the auxiliary
ground conductor 24 overlapping with each other. For the external
oblique view of the high-frequency signal transmission line 10c,
FIG. 1 will be referenced.
[0101] The high-frequency signal transmission line 10c differs from
the high-frequency signal transmission line 10a in the shape of the
bridge portion 60. More specifically, the high-frequency signal
transmission line 10c includes two types of bridge portions 60
arranged so as to alternate with each other. One type of bridge
portion 60 obliquely extends toward the positive end in the x-axis
direction when viewed in the direction toward the positive end in
the y-axis direction. The other type of bridge portion 60 obliquely
extends toward the positive end in the x-axis direction when viewed
in the direction toward the negative end in the y-axis direction.
Accordingly, the opening 30 is preferably in the shape of a
trapezoid, for example.
[0102] As with the high-frequency signal transmission line 10a, the
high-frequency signal transmission line 10c as above also renders
it possible to reduce insertion loss.
Fourth Modification
[0103] Hereinafter, a high-frequency signal transmission line 10d
according to a fourth modification of a preferred embodiment of the
present invention will be described with reference to the drawings.
FIG. 15 is an exploded view of a dielectric element assembly 12 of
the high-frequency signal transmission line 10d. FIG. 16 is a view
illustrating the high-frequency signal transmission line 10d with
the signal line 20 and the auxiliary ground conductor 24
overlapping with each other. For the external oblique view of the
high-frequency signal transmission line 10d, FIG. 1 will be
referenced.
[0104] The high-frequency signal transmission line 10d differs from
the high-frequency signal transmission line 10a in that the
reference ground conductor 22 includes openings 32 provided
therein, as shown in FIG. 15. As with the opening 30, the opening
32 is preferably in the shape of a parallelogram, for example, as
shown in FIGS. 15 and 16. In addition, the opening 32, when view in
a plan view in the z-axis direction, is positioned within the
boundaries of the opening 30. That is, the outer edge of the
opening 30 does not overlap with the outer edge of the opening
32.
[0105] Further, the high-frequency signal transmission line 10d
renders it possible to reduce insertion loss. More specifically, in
the high-frequency signal transmission line 10d, once a current
flows through the signal line 20, a feedback current (counter
current) flows through the reference ground conductor 22, and a
feedback current (counter current) flows through the auxiliary
ground conductor 24 as well. In the high-frequency signal
transmission line 10d, the outer edge of the opening 30 and the
outer edge of the opening 32 do not overlap with each other when
they are viewed in a plan view in the z-axis direction.
Accordingly, the portion of the reference ground conductor 22 where
the feedback current (counter current) flows and the portion of the
auxiliary ground conductor 24 where the feedback current (counter
current) flows are appropriately distant from each other. As a
result, coupling between the feedback currents (counter currents)
is weakened, so that the signal line 20 allows easy transmission of
current, and therefore, insertion loss in the high-frequency signal
transmission line 10d is reduced.
[0106] Still further, the reference ground conductor 22 preferably
includes the openings 32 provided therein and also includes a
plurality of bridge portions 62 provided between adjacent openings
32. The bridge portion 62 extends in the y-axis direction, and
crosses the thin portion 20b when viewed in a plan view in the
z-axis direction, as shown in FIGS. 15 and 16. The bridge portion
62 obliquely extends toward the positive end in the x-axis
direction when viewed in the direction toward the positive end in
the y-axis direction. Accordingly, the bridge portion 62, when
viewed in a plan view in the z-axis direction, crosses the thin
portion 20b obliquely.
[0107] As with the high-frequency signal transmission line 10a, the
high-frequency signal transmission line 10d as above also renders
it possible to reduce insertion loss.
[0108] Furthermore, in the high-frequency signal transmission line
10d, since the reference ground conductor 22 includes the openings
32 provided therein, less capacitance is generated between the
signal line 20 and the reference ground conductor 22. Thus, it is
possible to position the signal line 20 and the reference ground
conductor 22 close to each other without causing the characteristic
impedance of the signal line 20 to fluctuate significantly, whereby
the high-frequency signal transmission line 10d is reduced in
thickness.
Other Preferred Embodiments
[0109] The present invention is not limited to the high-frequency
signal transmission lines 10 and 10a to 10d according to the above
preferred embodiments, and changes are possible within the spirit
and scope of the present invention.
[0110] Furthermore, the configurations of the high-frequency signal
transmission lines 10 and 10a to 10d may be used in
combination.
[0111] The protective layers 14 and 15 have been described above as
being formed preferably by screen printing, but they may be formed
by photolithography, for example.
[0112] The high-frequency signal transmission lines 10 and 10a to
10d do not necessarily have the connectors 100a and 100b mounted
thereon. In such a case, the high-frequency signal transmission
lines 10 and 10a to 10d are connected at their ends to circuit
boards by solder or the like. Note that each of the high-frequency
signal transmission lines 10 and 10a to 10d may have only the
connector 100a mounted on one end.
[0113] Through-hole conductors may be used in place of the via-hole
conductors. The through-hole conductors are inter-layer connecting
portions, which are conductors formed, for example, by plating
inner circumferential surfaces of through-holes provided in the
dielectric element assembly 12.
[0114] The reference ground conductor 22 is not necessarily
provided.
[0115] The high-frequency signal transmission lines 10 and 10a to
10d may be used on RF circuit boards such as antenna front end
modules.
[0116] While preferred embodiments of the present invention have
been described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing from the scope and spirit of the present invention. The
scope of the present invention, therefore, is to be determined
solely by the following claims.
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