[Document Name]
DESCRIPTION
[Title of Invention]
BAND-PASS FILTER
5 [Technical Field]
[OOO 11
The present invention relates to a fin-line band-pass filter having a
wide selection for the band such as a microwave band or a millimeter wave
band.
10 [Background Art]
[0002]
As a band-pass filter for use in a microwave band or the like, a
waveguide filter is preferably used. The waveguide filter has a low loss
performance, and has high power durability suitable for applying large
15 amount of electric power so that the waveguide filter is widely used in
communication devices such as a base station device.
[0003]
An example of a waveguide filter is a fin-line band-pass filter.
The filter is a band-pass filter provided with rectangular waveguides
20 separated from each other along a middle of a broad width surface of the
filter, and a thin metal plate interposed between the rectangular
waveguides and designed to resoilate at a predetermined frequency. The
metal plate can be manufactured with high precision by etching or pressing.
Therefore, it is possible to secure the characteristics simply by assembling,
25 without adjusting the characteristics by using a screw. 'Thus, the filter
has an advantage that it is possible to reinarkably shorten the assembling
time and the inspectioll time.
[Citation List]
[Patent Literature]
3
[0004]
[PTL 11 International Patent Publication No. 20 101073554
[Summary of Invention]
[Technical Problem]
5 [0005]
A fin-line band-pass filter has a feature that a resonant frequency
and a coupling coefficient are determined by a thin metal plate to be
interposed. However, a well-known fin-line filter fails to secure a
sufficient coupling coefficient, and is difficult to be used in a wide
10 bandwidth or in a very high frequency band such as a millimeter wave band
(see PTL I).
[0006]
Further, in view of the manufacturing constraints on the thickness
of a thin metal plate, it is difficult to manufacture a thin metal plate
15 beyond a predetermined value. Therefore, as the size of a waveguide
decreases in order to handle a millinleter wave band or the like, the ratio of
a metal plate increases, whicl~m ay result in f ~ ~ r t ll~oewre ring the
implementable couplillg coefficient. Therefore, in particular, when
applying to high frequency such as a millimeter wave band, a fin-line filtcr
20 is difficult to be used.
[0007]
In view of the above, an object of the present invention is to
provide a fin-line band-pass filter providcd with rectangular waveguides
separated from each other along a 111iddle of a broad width surface of the
25 filter, and a thin metal plate interposed betwcen the rectallgular
waveguides and designcd to resonate at a predetermined frequency,
wherein the band-pass filter has an i~lcreased range of values of the
implementable coupling coefficie~lt,a nd a wide bandwidth requiring a lligll
coupling cocfficicnt.
[Solution to Problem]
[OOOS]
An aspect of the invention is directed to a band-pass filter provided
with rectangular waveguides separated from each other along a middle of a
5 broad width surface of the filter, and a metal plate interposed between the
rectangular waveguides, wherein at least one of coupling plates formed of
the metal plate is cut.
[Advantageous Effects of Invention]
[0009]
10 According to a fin-line band-pass filter of the present invention, it
is possible to implement a band-pass filter having an increased range of
values of the implementable coupling coefficient, and a wide bandwidth
requiring a high coupling coefficient.
[Brief Description of Drawings]
15 [0010]
Fig. 1 is an exploded perspective view of a fin-line band-pass filter
of an exenlplary enlbodiment of the present invention;
Fig. 2 is a perspective view of the fin-line band-pass filter after
assenlbling of the exemplary embodiment of the present invention;
20 Fig. 3 is an exploded perspective view of a fin-line band-pass filter
of an existing embodiment;
Fig. 4A is a diagram illustrating a structure of a metal plate of the
fin-line band-pass filter of the exemplary elnbodiment of the present
invention;
2 5 Fig. 4B is a diagram illustratillg a structure of a mctal plate of an
existing fin-line band-pass filter;
Fig. 5 is a diagram illustratil~ga relationship between a ripple band
and a coupling coefficient I<;
Fig. 6 is a diagram illustrating a relationship between the width W
5
of a coupling plate, and the coupling coefficie~ltI <;
Fig. 7 is a diagram illustrating a relationship between a gap D
between coupling plate portions, and the coupling coefficient k;
Fig. 8 is a diagram illustrating characteristics of the fin-line
5 band-pass filter of the exemplary embodiment;
Fig. 9A i s a diagram illustrating a structure of a coupling plate of
the fin-line band-pass filter of the exemplary embodiment;
Fig. 9B is a diagram illustrating a structure of a coupling plate of
the fin-line band-pass filter of the exemplary embodiment;
10 Fig. 9C i s a diagram illustrating a structure of a coupling plate of
the fin-line band-pass filter of the exemplary embodiment;
Fig. 9D i s a diagram illustrating a structure of a coupling plate of
the fin-line band-pass filter of the exemplary embodiment;
Fig. 10 is an exploded perspective view of the fin-line band-pass
15 filter of the exemplary embodiment of the present invention;
Fig. 11 is an exploded perspective view of a duplexes incorporated
with the fin-line band-pass filter of the exemplary embodiment of the
present i~lvention;a nd
Fig. 12 is an exploded perspcctivc view of the fin-line band-pass
20 filter of the exemplary enlbodiment of the present invention.
[Description of Embodiments]
[OOll]
Hereinafter, a most preferred exe~nplary embodimcnt of the present
invention is described in detail referring to the drawings. The exemplary
25 embodiment described in the following includes technically preferred
feat~rresi n order to carry out the present invention, but the scope of the
invention is not limited by t l ~ cfo llowing description.
(Ilescription of Structure)
Fig. 1 is an exploded perspcctivc view of a fin-line band-pass I'ilter
6
10 of a11 exemplary embodiment of the present invention. Fig. 2 is a
perspective view of the fin-line band-pass filter after assembling. The
fin-line band-pass filter 10 includes rectangular waveguides A1 and B2
separated fiom each other along a middle of a broad width surface of the
5 filter, and a thin metal plate 3 interposed between the rectangular
waveguides A1 and B2 and designed to resonate at a predetermined
frequency.
[OO 121
Cutting a coupling plate that determines the coupling between a
10 resonator 4 and an external portion makes it possible to strengthen the
coupling between the resonator 4 and the external portion, and to
implement a coupling coefficient required for obtaining intended
characteristics. In this example, a coupling plate that is cut is called as a
coupling plate a5, and a coupling plate that is not cut is called as a
15 coupling plate b6. In Fig. 1 and Fig. 2, only a first coupling plate and a
last coupling plate are cut among all the couplillg plates including the first
coupling plate and the last coupling plate. Alternatively, a coupling plate
or plates other than the f'irst coupling plate and the last coupling plate may
be cut depending on a required coupling coefficient.
20 (Ilescriplion of Operation)
A concrete example of a11 operation to be performed when some of
the coupling plates that determine a co~iplingc oefficient are cut is
described. In this example, a seven-stage band-pass filter using
rectangular waveguides (3.1 111111 x 1.55 mm) in the frcquency band of from
25 70 to 80 (;Hz is used. In data representing the concrete example, TElOl
mode, which is one of the propagation modes of a rectangular waveguide,
is used. Fig. 3 illustrates an example of a fin-line band-pass filter having
an existing metal plate shape. Fig. 4A and Fig. 4B illustrate respectively
partially enlarged views of a metal plate of the fin-line band-pass filter of
7
the present invention, and of a metal plate of an existing fin-line band-pass
filter.
[00 131
First, a reason why the existing metal plate structure fails to
5 implement a filter having a wide bandwidth is described. Fig. 5
illustrates a relationship between a ripple band and a coupling coefficient k
required for the first coupling plate. The coupling coefficient in this
example is the coupling coefficient used in a Chebyshev filter, and the
filter has a frequency of 73.5 GHz. The coupling coefficient required for
10 the first coupling plate (last coupling plate) is largest among the coupling
coefficients that determine the bandwidth of the filter. Therefore, in this
example, only the relationship between the ripple band and the coupling
coefficient of the first coupling plate is described. For instance, in order
to lnanufacture a filter, in which the center frequency is 73.5 GHz,
15 seven-stage, and the ripple band i s 6,000 MHz, it is necessary to set the
coupling coefficient of the first coupling plate to 0.53. I11 order to obtain
intended characteristics, it is necessary to satisfy the required coupling
coefficient. Deviation from the requircd coupling coefficient may
deteriorate the characteristics. In a fin-line filter, a structure that
20 determines the coupling coefficient is a coupling plate.
[0014]
Fig. 6 illustrates a relationship between the width W of a coupliilg
plate, and the coupling coefficient k in an existing structure. The width
W of a coupling plate is illustrated in Fig. 4B. In Fig. 6, the solid line
25 represents a structure, in which the thickness of a metal plate is set to 0.1
mnl. and the dotted line represents a structure, in which the thickness of a
metal plate is set to 0. 2 1111n. As the thickness o r a ~netalp late decreases,
and as the width of the metal plate decreases, the coupling coefficient
increases. I n view of the manufacturing constraints, however, the lower
8
limit of the width of a metal plate is substantially the same as the thickness
of the metal plate. It is not possible to decrease the thickness of a metal
plate to the limit in view of the strength of the metal plate. Taking into
consideration the productivity in assembling or the like, the thickness of a
5 metal plate is at most about 0.1 mm. The maximum allowable value of
the coupling coefficient in this case i s 0.39.
[00 151
In implementing a band-pass filter, in which the center frequency is
73.5 GHz, seven-stage, and the ripple band is 6,000 MHz as exemplified
10 above, the conventional structure fails to achieve the coupling coefficient
of 0.53, regardless that 0.53 is necessary as the coupling coefficient of the
first coupling plate (last coupling plate). In the existing structure, it is
limited to the band-pass filter having a ripple band of 3,000 MHz or lower
to be implemented. For the aforementioned reason, the existing metal
15 plate structure fails to implement a filter having a wide bandwidth so that
the coupling plate of the exemplary embodiment having a shape capable of
increasing thc coupling coefficient is advantageous.
[0016]
Fig. 7 illustrates a relationship between the gap D between coupling
20 plate portions, and the coupling coefficient k. The gap D between
coupling plate portions is illustrated in Fig. 4A. I11 this example, the
width W of a metal plate is set to 1 rnm. As the gap D between coupling
plate portions increases, the coupling coefficient increases. Cutting
some of the coupli~lgp lates that separate rcsol~atorsf rom each other
25 (separate a resollator from an external portion) makes it possible to
strengthen the coupling between the resonators, and to increase the
couplillg coefficient. For instance, when the gap 11 bctwcen coupling
plate portions is set to about 0.6 mm, the c o ~ ~ p l i icl go efficient becomes
0.53. 'I'l~us, i t is possible to irnplelnerlt a band-pass filter having a ripple
9
band of 6,000 MHz, which could not be implemented by the existing
structure.
[00 171
Fig. 8 illustrates characteristics of a fin-line band-pass filter
5 designed with use of the structure of the exeinplary embodiment. The
solid line represents insertion loss S21, and the dotted line represents
return loss S11. The filter has a metal plate, in which only the first
coupling plate and the last coupling plate are cut. The filter provides
enhanced characteristics. In this example, the characteristics of a filter,
10 in which only the first coupling plate and the last coupling plate are cut
among all the coupling plates including the first coupling plate and the last
coupling plate, are described. Alternatively, a coupling plate or plates
other than the first coupling plate and the last coupling plate may be cut
depending on a required coupling coefficient. As described above, use of
15 the structure of the exenlplary embodiment makes it possible to implement
a coupling coefficient that could not be implemented by the existing
structure, and makes it possible to implement a filter of a wide bandwidth.
[00 181
In the foregoing description, TElOl mode, which is one of the
20 propagation modes of a waveguide, is used. Use of the exemplary
embodiment makes i t possible to coilfigure a fin-line band-pass filter at a
higher order mode, such as TE102 mode or TE103 mode. Use of a higher
order mode is advailtageous in creating a filter with less variation with
respect to size error. When TE102 inode is used, sensitivity with respect
25 to size crror is reduced to half, as compared with the case of using TE101
mode. I-lowever, use of a higher order inode may increase t l ~ cc oupliilg
coefficient necessary for iinplementing a filter havillg the same bandwidth.
Therefore, use of the structure of the exemplary embodiment capable of
irnplementil~ga larger coupling coefficient makes it possible to create a
10
filter, in which a high order inode such as TE102 or TI03 is used, and
variation with respect to size error is small. Further, since variation with
respect to size error is small, the necessity of adjusting the characteristics
by using a screw is reduced, resulting in a cost reduction.
5 [0019]
In the description of the fin-line band-pass filter of the exemplary
embodiment, the number of stages of the filter used is seven. The number
of stages of the filter is designed depending on a required pass-band and a
required amount of attenuation, and does not limit the scope of the
10 invention. Further, as illustrated in Figs. 9A to 9D, it is possible to
modify the cutting manner of a coupling plate a5. It is possible to secure
the characteristics, even when the corner of the coupling plate a5 is
rounded or the widths of both ends of the coupling plate a5 are different
from each other.
15 [0020]
Fig. 10 is a diagram illustrating a configuration, in which the shape
of a filtcr is modified. In this case, the invention is also applicable to a
curved filter. The filter may not necessarily be a linear filter. Further,
Fig. 1 1 is a diagram illustrating a duplexes configured with two filters and
20 a '1'-junction. The band-pass filter having the structure of the present
invention may also be applied to a duplexes or a multiplexer. l'11e shape
of the filter or the position of a port 34 is designed in confornlity with the
interface of a device, and does not limit the present invention.
[OO2 11
2 5 Fig. 12 is a diagram illustrating a configuration, in which a printed
circuit board is used, in place of a nletal plate. Fornling coupling plates
and resonators by a metal layer pattern on a printed circuit board 43 maltes
it possible to configure a fin-linc band-pass filter in the same ~llannera s in
the case of using a metal plate. Use of a printed circuit board is
11
advantageous in formillg a filter, an amplifier, and the like on one substrate,
which makes it easy to connect the members to each other. Use of a
printed circuit board makes it possible to form a waveguide, a microstrip
line converter, and the like on the printed circuit board.
5 [0022]
According to the present invention, in view of the characteristics of
the fin-line band-pass filter of the exemplary embodiment above mentioned,
it is possible to increase the coupling coefficie~lt. Therefore, it is
possible to create a fin-line band-pass filter having a wide bandwidth.
10 Further, it is possible to use a high order mode such as TE102 mode or
TE103 mode, which makes it possible to create a filter with less variation
with respect to size error. Furthermore, since variation with respect to
size error is small, the necessity of adjusting the characteristics by using a
screw i s reduced. This is advantageous in reducing the cost. In
15 addition, rcsonators can be formed of one plate, which makes it possible to
shorten the assembling time, and the adjust~nelltt ime using a screw. This
is advantageous in reducing the cost.
loo231
The present illvelltioll is not limited to the foregoing exemplary
20 embodime~lt and examples thereof, and nay be modified in various ways as
far as such modificatiolls lie within the scope of the invention hereinafter
defined. It is needless to say that such modificatiol~sl ie in the scope of
the invention.
LO0241
2 5 This application claims the priority based on Japallese I'atcnt
Application No. 2012-196858 filed on September 7. 2012, and all of the
disclosure of which is hereby incorporated.
[Illdustrial Applicability]
[0025]
12
The present invention relates to a fin-line band-pass filter for use in
a microwave band or a millimeter wave band.
[Reference signs List]
[0026]
5 1, 2 1, 3 1, 4 1 Rectangular waveguide A
2, 22, 32, 42 Rectangular waveguide B
3, 23, 33 Metal plate
34 Port
4 Resonator
5 Coupling plate a
6 Coupling plate b
10 Fin-line band-pass filter
43 Printed circuit board
44 Via

WE CLAIM:
[Clain~I ]
A band-pass filter comprising:
rectangular waveguides separated from each other along a middle of
5 a broad width surface of the filter; and
a metal plate interposed between the rectangular waveguides,
wherein
at least one of coupling plates formed of the metal plate is cut.
[Claim 21
10 The band-pass filter according to Claim 1, wherein
the coupling plate formed on an end of the metal plate, among the
coupliilg plates, i s cut.
[Claim 31
The band-pass filter according to Claim 1, wherein
15 the two coupling plates formed on both ends of the metal plate,
anlong the coupling plates, i s cut.
(Claim 41
The band-pass filter according to any one of Clainls 1 to 3, wherein
a portion of the cut coupling plate has a linear shape.
20 [Claim 51
l'he band-pass filter according to ally one of Claims 1 to 3, wherein
a portion of the cut coupling plate has a curved shape.
[Claim 61
'T'he band-pass filter according to any one of Claims 1 to 3. wherein
2 5 a portion of the cut coupling plate has a step shape.
[Clailn 71
A band-pass filter comprising:
curved waveguides separated from each other along a nliddle of a
broad width surface of the filter; and
14
a metal plate interposed between the curved waveguides, wherein
at least one of coupling plates formed of the metal plate is cut.
[Claim 81
The band-pass filter according to Claim 7, wherein
5 the curved waveguide has a U-shape.
[Claim 91
A band-pass filter comprising:
a plurality of filter elements connected to each other, wherein
each of the filter elements is provided with a band-pass filter of any
10 one of Claims 1 to 8.
[Claim 101
The band-pass filter according to any one of Claims 1 to 9, wherein
the metal plate is formed of a metal layer pattern on a printed
circuit board.
15
Dated this 0 3 r d Day of March 2015