1. A band-pass filter, comprising: a dielectric substrate having an upper surface and a lower surface opposed to each other, 5 the dielectric substrate extending in a waveguide axial direction; a pair of conductor layers respectively arranged on the upper surface and the lower surface of the dielectric substrate; two rows of through hole groups for sidewalls, which are formed at predetermined intervals in the waveguide axial direction so as to electrically connect the pair of conductor 10 layers; and a plurality of through holes for electrically connecting the pair of conductor layers, the plurality of through holes being formed in parallel to the waveguide axial direction and arranged in a center of a waveguide formed in a region surrounded by the pair of conductor layers and the two rows of the through hole groups for sidewalls.

2. The band-pass filter according to claim 1, wherein the predetermined interval is about 0.3 wavelength or less.

3. The band-pass filter according to claim 2, wherein each of the through hole groups 20 for sidewalls in the two rows has a diameter of 1.2 mm, and the predetermined interval is 2.4 mm.

4. 'T'he band-pass filter according to claim 3, wherein the plurality of through holes comprise one through hole formed in each of both end portioils and groups of a plurality of 25 through holes arranged at i~ltervalsb etween the both end portions.

5. The band-pass filter according to claim 4, wherein a number of the plurality of through holes included in each of the groups is four.

6. The band-pass filter according to any one of claims 3 to 5, wherein each of the plurality of through holes has a diameter of 0.6 mm.

Title of the Invention
RAND-PASS FILTER
5
Technical Field
This invention relates to a band-pass filter, in particular, a band-pass waveguide filter
which is realized equivalently in a dielectric substrate.
10 Background Art
Currently, in the development of high-frequency radio devices, the realization of
low-loss connections for integration of various types of high-frequency circuits and the cost
reduction and mass production of each element circuit are required. Therefore, the realization
of the high-frequency radio device with a small space while maintaining high-performance and
15 high-functional characteristics is a key factor. In the high-frequency radio device, physical
dimensions of a passive circuit such as a filter are substantially determined by a design frequency.
Therefore, the passive circuit such as the filter is one of circuits which have a low degree of
freedom in view of flexible mounting of each of components thereof.
A related band-pass filter is realized by sandwiching an E-plane parallel metal plate
20 between rectangular waveguides obtained by dividing a rectangular waveguide into two in the
middle of an H-plane to configure a single waveguide. In the case of the above-mentioned
structure, the metal plate which is a mechanism element with high manufacturing accuracy and
the rectailgular waveguides which are sub-jectcd to cutting work are required. In terms of the
connection to and the integration with planar circuits in the peripl~ery,a mounting space is
25 required.
Therefore, a technology of equivalently realizing a band-pass waveguide filter in a
dielectric substrate has hitherto been proposed.
For example, in JP-A-11-284409 (Patent Document I), tl~creis disclosed a "waveguide
band-pass filter" which has high productivity and can meet a requirement of size reduction.
30 The waveguide band-pass filter disclosed in Patent Document 1 comprises a pair of main
conductor layers sandwiching a dielectric substrate therebetween, and two rows of through
conductor groups for sidewalls ibrmed at intervals slnaller than 112 of a signal wavelength in a
signal tra~lsmissiond irection so as to electrically connect the lvain conductor layers. A plurality
of through conductors, which electrically connect the main conductor layers to fornl inductive
windows (inductive elements), are provided at intervals smaller than 112 of a wavelength in the
waveguide in the signal transrnissioi~d irection inside a dielectric waveguide line for transmitting
a high-fi-equency signal through a region surrouilded by the pair of maill conductor layers and the
two rows of through conductor groups for sidewalls.
5 In an example of one embodiment of Patent Document 1, as the plurality of through
conductors, a maximum number (three in the embodiment) of through conductors are formed in
an approximately middle portion of the dielectric waveguide line so as to be separated away
from each other in a width direction. As separating away from the middle portion to both sides
in the signal transmission direction, the number thereof decreases.
10
Prior Art Document
Patent Document
Patent Document 1 : JP-A- 1 1-284409
15 Disclosure of the Invention
Problem to be Solved by the Invention
In the waveguide band-pass filter disclosed in Patent Document 1, the plurality of
through conductors are for~ncdin the approximately middle portion of the dielectric waveguide
line so as to be separated away from each other in the width direction. Therefore, there is a
20 problem in that electrical characteristics degrade when the positions of the through conductors
vary in the width direction.
It is an object of this invention to provide a band-pass filter capable of preventing
electrical characteristics from degrading.
Means to Solve the Problem
25 A band-pass filter according to this invention includes: a dielectric substrate having an
upper surface and a lower surface opposed to each other, the dielectric substrate extending in a
waveguide axial direction; a pair of conductor layers respectively arranged on the upper surface
and the lower surface of the dielectric substrate; two rows of through hole groups for sidewalls,
which are formed at predetermined intervals in the waveguide axial direction so as to electrically
30 connect the pair of collductor layers; and a plurality of through holes for electrically connecting
the pair or conductor layers, the plurality of through holes being formed in parallcl to the
waveguide axial direction and arranged in a center of a waveguide formed in a region surrounded
by the pair of conduclos layers and the two rows of the through hole groups for siclewalls.
Effect of the Invention
The band-pass filter according to this invention is capable of preventing electrical
characteristics from degrading.
Brief Description of the Drawings
5 Fig. 1 is a partially cutaway exploded perspective view illustrati~lga configuration of a
related band-pass waveguide filter;
Fig. 2 is a characteristic graph showing the results of analysis of frequency
characteristics of S parameters of the related band-pass waveguide filter illustrated in Fig. 1 by
an electromagnetic field simulation;
10 Fig. 3 is a perspective transparent view illustrating a structure of a band-pass filter
according to a first example of this invention; and
Fig. 4 is a characteristic graph showing the results of analysis of frequency
characteristics of S parameters of the band-pass filter illustrated in Fig. 3 by an electromagnetic
field simulation.
15
Mode for Embodying the Invention
[Related Art]
Referring to Fig. 1, a configuration of a related band-pass waveguide filter 10 is now
described for easy understanding of this invention. Fig. 1 is a partially cutaway exploded
, 20 perspective view illustrating the configuration of the related band-pass waveguide filter 10.
In the example of Fig. 1, an orthogonal coordinate system (x, y, z) has an x direction
which extends literally, a y direction which extends vertically, and a z direction which extends
longitudinally. The x direction, the y direction, and the z direction are orthogonal to one
another. The x direction is also referred to as a horizontal direction or a width direction. The
25 y direction is also referred to as a vertical direction, a thickness direction, or a height direction.
'The z direction is also referred to as a longitudinal direction. A signal (electromagnetic wave)
is transmitted (propagated) in the z direction. Therefore, the z direction is also referred to as a
signal transmissioll direction (waveguide axial direction).
The band-pass waveguide filter 10 comprises rectangular waveguide sidewalls 11
30 obtained by dividing a rectangular waveguide into two in the middle of an H-plane, and an
E-plane parallel metal plate 12. By sa~ldwichii~thge E-plane parallel metal plate 12 between
the rectangular waveguide sidewalls 11 obtained by the division, a single waveguide is
configured. '1.11~ E-plane parallel nletal plate 12 determil~esa coupling coefficient required for
the band-pass filter based on a shape of metal plates (such as a plate thickness or a width of a
metal fin, and intervals between metal fins) arranged in a ladder-like pattern.
Each of the rectangular waveguide sidewalls 11 has a U-like cross section and has a
width W of 7.9 mm, a height (thickness) H of 7.9 Inm, and a length L1 of 124 mm.
The E-plane parallel metal plate 12 comprises two metal pieces 122 which are arranged
5 in parallel so as to be separated away from each other in the vertical direction (y direction) and
extend in the signal transmission directiol~(z direction), and a plurality of metal plates 124
arranged in a ladder-like pattern between the two metal pieces 122. The metal plates 124 are
also referred to as metal fins. The metal fins 124 function as inductive elements. A shape of
the metal fins 124 (such as a plate thickness, a width of the metal fin, and intervals between the
10 metal fins) determines a coupling coefficient required for the band-pass filter.
Fig. 2 is a characteristic graph showing the results of analysis of frequency
characteristics of S parameters of the related band-pass waveguide filter 10 by an
electromagnetic simulation. A horizontal axis of Fig. 2 represents a frequency [GNz], whereas
a vertical axis represents S21 [dB] and S 11 [dB] of the S parameters.
15 As well known in the field of art, as the S parameters, S21 corresponds to an insertion
loss and Sl1 corresponds to a return loss. The insertion loss S21 is a loss of a signal (power)
passing through a terminal 2 (output terminal) when the signal is input to a terminal 1 (input
terminal), which is expressed in dB (decibels). The return loss Sl1 is a loss of a signal (power)
that is reflected and returned to the terminal 1 (input terminal) when the signal is input to the
20 terminal 1 (input terminal), which is expressed in dB (decibels).
In the case of the structure of the related band-pass waveguide filter 10 illustrated in Fig.
1, the E-plane parallel metal plate 12 which is a mechanical component with high manufacturing
accuracy and the pair of recta~lgularw aveguide sidewalls 11 obtained by cutting work are
required. In terms of the connection to and the integration with planar circuits in the periphery,
25 a mounting space is required.
On the other hand, in the waveguide band-pass filter disclosed in Patent Document 1,
the plurality of through conductors are formed in the approximately middle portion of the
dielectric waveguide line so as to be separated away from each other in the width direction.
Therefore, there is a problem in that electrical characteristics degrade when the positions of the
30 through conductors vary in the width direction.
[Exemplary Embodin~ent]
A feature of this invention is now described.
This invention has a feature in that througl~h oles are arrailgcd in a diclcctric substrate to
forn~a waveguidc and inductive coupli~lge lements, thereby realizing a band-pass filter.
In this invention, metal-plated through holes are arranged as the waveguide sidewalls to
form a waveguide. 'I'he metal fin portions are replaced by through holes. In this manner, a
band-pass filter equivalent to that described above is configured.
With the configuration described above, the filter can be realized in the dielectric
Fi substrate and is suitable for the connection to and the integration with plailar-line based
high-frequency circuits (RF circuits) in the periphery. Moreover, mechanism elements which
require high manufacturing accuracy such as the metal platc and the rectangular waveguide are
unnecessary. Therefore, the band-pass filter is reduced in size by a relative permittivity and
therefore is advantageous in view of the mounting space.
10 In other words, in this invention, the band-pass filter is realized by arranging the
metal-plated through holes inside the dielectric substrate having the metal-bonded upper and
lower surfaces. The band-pass filter can be manufactured by a conventional printed-board
processing technology without requiring the mechanism elements. Moreover, the band-pass
filter is reduced in size by a permittivity of the substrate, can be manufactured by the
15 conventional printing technology, and is suitable for the connection to and integration with the
planar circuits in the periphery in the same substrate.
In other words, this invention has a feature in that the E-plane band-pass waveguide
filter using the inechanism elements such as the conventional metal plate and rectangular
waveguide is configured by "replacement" with the metal-plated through holes.
2 0 From the point of view described above, an initial design is made with a closed
waveguide requiring a small calculation load, and a final design can be determined in view of the
through holes. Therefore, it is easy to plan the design, providing excellent design performance.
The band-pass filter is configured only by arranging the through holes in a substrate
thickness direction and thereforc has a two-dimensional structure which is uniform in the
25 thickness direction (y direction). Therefore, the band-pass filter is advantageous in terms of
manufacture, analysis, and design.
The through holes located in the middle portion of the waveguide are arranged in
parallel to the waveguide axis (z direction). As describcd above, the through holes for
determining the coupling coefficient are arranged in the center of the waveguide. Therefore,
30 the degradation of the electrical characteristics occurring when the positioi~so f the through
conductors vary in the width direction (x direction) as in the case of Patent Document 1 can be
prevented. This is because an electro~nagneticf ield in the waveguide has a peak value of a sine
distribution in tlie vicinity of the center of thc waveguide axis and is resistant to a manufacturing
error.
[First Example]
Fig. 3 is a perspective transparent view illustrating a structure of a 13 GHz-band model
band-pass filter 20 according to a first example of this is~vention.
I11 the example of Fig. 3, an orthogonal coordiilate system (x, y, z) has an x direction
5 which extends literally, a y direction which extends vei-tically, and a z direction which extends
longitudinally. The x direction, the y direction, and the z direction are orthogonal to one
another. The x direction is also referred to as a horizontal direction or a width direction. The
y direction is also referred to as a vertical direction or a thickness direction. The z direction is
also refes~edto as a longitudinal direction. A signal (electromagnetic wave) is transmitted
10 (propagated) in the z direction. Therefore, the z direction is also referred to as a signal
transmission direction (waveguide axial direction).
The illustrated band-pass filter 20 is a design example with a design frequency of 13.6
GHz, a passband of 200 MHz, and an attenuation of 40 dB at *200 MHz away from a center
frequency, and has a six-stage configuration.
15 The band-pass filter 20 includes a dielectric substrate 2 1 having a cuboid shape with a
thickness T of 1.6 mm and a length L2 of 100 msn. The dielectric substrate 21 extends in the
waveguide axial direction (z direction). Onto an upper surface and a lower surface of the
dielectric substrate 2 1, each of a pair of conductor layers 22 made of a metal is bonded.
Two rows of metal-plated through holes 23 are arranged in the dielectric substrate 21 so
20 as to be separated away from each other at a distance S of 10.8 min in the width direction (x
direction). The metal-plated through holes 23 electrically connect the pair of conductor layers
22 to each other. The metal-plated through holes 23 in each of the rows are arranged so as to
extend in the waveguide axial direction (z direction) at intervals of about 0.3 wavelength or less
and function as a sidewall. In the illustrated example, each of the rows of the metal-plated
25 through holes 23 is formed by arranging through holes each having a diameter of 1.2 mm at
intervals of 2.4 mm.
In a region surrounded by the pair of conductor layers 22 and the two rows of the
metal-plated through holes 23, a waveguide (22; 23) is configured (formed).
'Therefore, a portion corresponding to the rectangular waveguide sidewalls 11 illustrated
30 in Fig. 1 corresponds to a portion of the metal-plated through holes 23 arranged on both sides
illustrated in Fig. 3.
The metal-plated through holes 23 arranged on both sides are also referred to as through
hole groups for sidewalls in two rows.
The band-pass filter 20 h~rtherc omprises a plurality of througl~h oles 24 arrangecl in the
center (middle) of the waveguide (22; 23). The plurality of through holes 24 electrically
connect the pair of conductor layers 22. The plurality of through holes 24 are arranged in the
center of the waveguide (22; 23) in parallel to the waveguide axial direction (z direction).
Specifically, in the band-pass filter 20, a portion of the inductive elements 124
5 corresponding to the E-plane parallel metal plate 12 provided in the center of the H-plane of the
waveguide illustrated in Fig. 1 is configured by the metal-plated through holes 24 arranged in the
center of the waveguide (22; 23). In other words, a portion corresponding to the metal fins
(inductive elements) 124 illustrated in Fig. 1 corresponds to a portion of the metal-plated through
holes 24 arranged in the center in Fig. 3.
10 In the case of the band-pass waveguide filter 10 illustrated in Fig. 1, a coupling
coefficient required for a desired band-pass filter is determined based on the shape of each of the
metal fins 124 of the E-plane parallel metal plate 12, which are arranged in the ladder-like
pattern.
On the other hand, in the band-pass filter 20 illustrated in Fig. 3, a coupling coefficient
15 required for a desired band-pass filter is determined based on the number, a radius, and positions
of the metal-plated through holes 24 arranged in the middle of the H-plane of the waveguide.
In this case, in order to achieve an appropriate coupling coefficient, a diameter of each of the
through holes 24 is set to 0.6 mm. This structure can be realized by a printing technology and
is suitable for the integration with planar circuits in the periphery in the same substrate 2 1.
2 0 In the illustrated example, the number of metal-plated through holes 24 arranged in the
middle is five groups of four through holes and two individual through holes, that is, twenty two
in total. Specifically, as the mctal-plated through holes 24 arranged in the middle, the
individual through holes and the groups of four through holes are arranged at intervals.
However, the number and the position of arrangement of the through holes 24 are not limited to
25 those described above and variously changed depending on the design frequency.
Next, operation and effects of the band-pass filter 20 illustrated in Fig. 3 are described.
The metal-plated through holes 23 arranged at about 0.3 wavelength or less in the
direction parallel to the E-plane (y direction) have a small leakage loss of power between the
through holes 23 and therefore operate in thc dielectric substrate 21 equivalently as metal walls.
3 0 Thus, by arranging the metal-plated through holes 23 at appropriate positions, the
conventional mctal wall portions of the band-pass waveguide filter 10 including the E-plane
parallel metal plate 12 can be replaced by the metal-plated through holes 23.
According to this example, the band-pass filter 20 can be configured by the
co~lventio~lparli nting technology or arranging the metal-plated through holes 23 and 24 in the
dielectric substrate 21 having the upper and lower surfaces onto which the metals 22 are bonded,
without using three-dimensional mechanism elements such as the rectangular waveguide whicl~
is subjected to cutting work and the E-plane parallel metal plate. The band-pass filter can be
realized in the dielectric substrate 2 1 and therefore is suitable for the integration with planar-line
5 based high-frequency circuits in the periphery in the same substrate 21.
Moreover, this structure is uniform in the thickness direction (y direction) and therefore
can be realized with the dielectric substrate 21 having any thickness. Thus, excellent design
performance is provided.
The band-pass filter is configured in the dielectric substrate 2 1 and is therefore reduced
10 in size in proportion to the reciprocal of the square root of the relative permittivity of the
dielectric substrate 2 1, thus providing advantages even in view of the mounting space. For
example, when a Teflon (trademark) substrate (having a relative permittivity of 2.2) is used as
the dielectric substrate 2 1. the dimensions are reduced from 15.8 mm to 10.8 mm in the width
direction (x direction) and from 124 mm to 100 mm in the waveguide axial direction (z
15 direction) in the case of the 13 GHz-band model.
As an example, Fig. 4 shows the results of analysis of frequency characteristics of the S
parameters of the 13 GHz-band model band-pass filter 20 by an electromagnetic simulation. In
Fig. 4, a horizontal axis represents a frequency [GHz], whereas a vertical axis represents S21
[dB] and S 11 [dB] of the S parameters.
2 0 When a Teflon substrate (having the relative permittivity of 2.2 and tan6=0.00085) is
used as the dielectric substrate 2 1, a passband of about 200 MHz and an attenuation of about 40
dB at 200 MHz away are realized.
As is apparent from the comparison with Fig. 2, characteristics substantially equivalent
to those of the related band-pass waveguide filter 10 (Fig. 1) are realized as attenuation
25 characteristics except for the insertion loss S21 in a passband. The insertion loss S21 increases
to about 3.0 dB as compared with that of the related band-pass waveguide filter 10. The
increase is principally attributed to a dielectric loss and is highly expected to be improved by
selecting a material having small tan 6.
Next, effects of the first example of this invention will be described.
The effects of the first example are to prevent the degradation of the electrical
characteristics. This is because the metal-plated through holes 24 are arranged in the center of
the waveguide in parallel to the waveguide axial direction (z direction).
While the invention has been particularly sl~owna nd dcscribed with reference to an
example thereof, the invention is not limited to this example. It will be understood by those of
ordinary skill in the art that various changes in form and details may be made thereill without
departing from the spirit and scope of the invention as defjned by the claims.
Illdustrial Applicability
5 This invention can be used for an RF transmission/reception separating circuit included
in an input section of a simplified radio device for the purpose of constructing a low-cost flexible
backbone network system.
Reference Signs List
10 20 ... band-pass filter
2 1 -.. dielectric substrate
22 ... conductor layer
23 ... metal-plated through holes arranged on both sides (through hole group for sidewall)
24 ... metal-plated through hole arranged in center
15
This application is based upon and claims the benefit of priority from Japanese Patent
Application No. 20 12- 12706 1, filed on June 4,20 12, the disclosure of which is incorporated
herein in its entirety by reference.

WE CLAIM:-
1. A band-pass filter, comprising:
a dielectric substrate having an upper surface and a lower surface opposed to each other,
5 the dielectric substrate extending in a waveguide axial direction;
a pair of conductor layers respectively arranged on the upper surface and the lower
surface of the dielectric substrate;
two rows of through hole groups for sidewalls, which are formed at predetermined
intervals in the waveguide axial direction so as to electrically connect the pair of conductor
10 layers; and
a plurality of through holes for electrically connecting the pair of conductor layers, the
plurality of through holes being formed in parallel to the waveguide axial direction and arranged
in a center of a waveguide formed in a region surrounded by the pair of conductor layers and the
two rows of the through hole groups for sidewalls.
2. The band-pass filter according to claim 1, wherein the predetermined interval is about
0.3 wavelength or less.
3. The band-pass filter according to claim 2, wherein each of the through hole groups
20 for sidewalls in the two rows has a diameter of 1.2 mm, and the predetermined interval is 2.4
mm.
4. 'T'he band-pass filter according to claim 3, wherein the plurality of through holes
comprise one through hole formed in each of both end portioils and groups of a plurality of
25 through holes arranged at i~ltervalsb etween the both end portions.
5. The band-pass filter according to claim 4, wherein a number of the plurality of
through holes included in each of the groups is four.
6. The band-pass filter according to any one of claims 3 to 5, wherein each of the
plurality of through holes has a diameter of 0.6 mm.