Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2001-02-13
2004-04-13
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S219000
Reexamination Certificate
active
06720848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual mode band-pass filter for use in, for example, communications equipment operating in the range of the microwave band to the milliwave band.
2. Description of the Related Art
Conventionally, different types of dual mode band-pass filters have been proposed as a band-pass filter for use in a high frequency band as described in “MINIATURE DUAL MODE MICROSTRIP FILTERS”, J. A. Curtis and S. J. Fiedziuszko, 1991 IEE MTT-S Digest.
FIGS. 48 and 49
are schematic plan views illustrating conventional dual mode band-pass filters, respectively.
In a band-pass filter
200
shown in
FIG. 48
, a circular conductive film
201
is provided on a dielectric substrate (not shown). Input-output coupling circuits
202
and
203
are coupled to the conductive film
201
so as to define an angle of 90° relative to each other. A tip-open stub
204
is disposed on the conductive film
201
at a position that defines a central angle of 45° relative to the input-output coupling circuit
203
. Thereby, two resonance modes with different resonance frequencies are coupled together. Thus, the band-pass filter
200
is configured so as to operate as a dual mode band-pass filter.
In a dual mode band-pass filter
210
shown in
FIG. 49
, a substantially square conductive film
211
is disposed on a dielectric substrate. Input-output coupling circuits
212
and
213
are connected to the conductive film
211
so as to define an angle of 90° relative to each other. The corner of the conductive film
211
in the position thereof defining an angle of 135° with respect to the input-output coupling circuit
213
is cut away. The resonance frequencies in two resonance modes are made different from each other by the cut portion
211
a
, so that the two resonance modes having different resonance frequencies are coupled to each other. Thus, the band-pass filter
210
can be operated as a dual mode band-pass filter.
On the other hand, there has been proposed a dual mode band-pass filter that contains a ring-shape conductive film instead of the circular conductive film (Japanese Unexamined Patent Application Publication No. 9-139612 and No. 9-162610). In particular, a dual mode filter is disclosed, in which a ring-shaped ring transmission line is used, input-output coupling circuits are arranged so as to define a central angle of about 90° similarly to the dual mode band-pass filter
200
shown in
FIG. 48
, and a tip-open stub is provided in a portion of the ring transmission line.
Moreover, Japanese Unexamined Patent Application Publication No. 6-112701 discloses a dual mode band-pass filter that uses a ring transmission line similar to the above-mentioned transmission line. As shown in
FIG. 50
, in the dual mode filter
221
, a ring resonator includes a ring conductive film
222
disposed on a dielectric substrate. In this case, four terminals
223
to
226
are disposed on the ring conductive film
222
so as to define an angle of 90° relative to each other with respect to the center of the ring conductive film
222
. Two of the four terminals arranged at the positions defining an angle of 90° relative to each other with respect to the center of the ring conductive film are connected to input-output coupling circuits
227
and
228
, respectively. The remaining two terminals
225
and
226
are connected to each other via a feedback circuit
230
.
Moreover, it is described that in the ring resonator including one strip line and having the above-described configuration, perpendicular resonance modes, which are not coupled to each other, are generated, and the coupling degree is controlled by the above-mentioned feedback circuit
230
.
In the conventional dual mode band-pass filters shown in
FIGS. 48 and 49
, a two step band-pass filter can be formed by forming one conductive film pattern. Accordingly, the band-pass filter can be miniaturized.
However, the dual mode band-pass filters each have the configuration in which the input-output coupling circuits, which are separated from each other by a particular angle, are coupled to each other in the circular or square conductive film pattern. Therefore, the dual mode band-pass filters have the disadvantage that the coupling degree cannot be increased, and a wide pass band cannot be achieved.
In the band-pass filter shown in
FIG. 48
, the conductive film
201
is restricted to a circular shape. In the band-pass filter shown in
FIG. 49
, the conductive film
211
is also limited to a substantially square shape. Thus, there is the problem that the design flexibility is low.
Dual mode band-pass filters
221
using such a ring resonator as described in Japanese Unexamined Patent Application Publication Nos. 9-139612 and 9-162610 have the problem that it is difficult to improve the coupling degree, and the shape and size of the ring resonator are restricted.
On the other hand, in the dual mode band-pass filter
221
described in Japanese Unexamined Patent Application Publication No. 6-112701, the coupling degree is controlled, and the band-width can be widened by use of the feedback circuit
230
. However, in the conventional dual mode filter, the feedback circuit
230
is required. Thus, the circuit configuration becomes complicated. Furthermore, the shape and size of the ring resonator are limited to a ring-shape, so that the design flexibility is very low.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a dual mode band-pass filter that is miniaturized and has a greatly improved coupling degree that is easily adjusted and a very wide pass band, while also having very high design flexibility.
According to a preferred embodiment of the present invention, a dual mode band-pass filter includes a dielectric substrate having first and second main surfaces, a metallic film having an opening for coupling two resonance modes and disposed in the first main surface of the dielectric substrate or inside of the dielectric substrate, at least one ground electrode disposed on the second main surface of the dielectric substrate or inside of the dielectric substrate, so as to be opposed to the metallic film through a dielectric layer, and a pair of input-output coupling circuits connected to different portions of the metallic film. With the above-described unique configuration, one of the two resonance modes, that is, one propagated substantially parallel to an imaginary straight line passing through the connection points at which the pair of the input-output coupling circuits are connected to the metallic film, and the other propagated substantially perpendicularly to the imaginary line, is affected by the opening so that the resonance frequency is varied. In other words, the opening is arranged to exert an influence over the resonance current of one of the resonance modes whereby the one resonance mode can be coupled to the other resonance mode. Thus, the opening causes the two resonance modes to be coupled to each other, and as a result, the filter can be operated as a dual mode band-pass filter.
Preferably, the opening has a shape containing a longitudinal dimension and a width dimension.
Also preferably, the plan shape of the opening is a rectangle, an ellipse, or a configuration including a rectangle or ellipse having a bent portion thereof elongating in a direction intersecting the longitudinal dimension thereof.
It is also preferred if the plan shape of the opening is a rectangle, a rhombus, a regular polygon, a circle, or an ellipse.
In addition, a plurality of openings may be formed.
Preferably, the metallic film is disposed on the first main surface of the dielectric substrate, and the ground electrode is disposed on the second main surface of the dielectric substrate.
Also preferably, the metallic film is disposed at a vertical level inside of the dielectric substrate, and the ground electrodes are disposed on the first and second main surfaces of the dielectric substrate, whereby the band-pass filter h
Kanba Seiji
Mizoguchi Naoki
Okamura Hisatake
Jones Stephen E.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Pascal Robert
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