Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2002-04-05
2004-10-26
Wells, Kenneth B. (Department: 2816)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S208000
Reexamination Certificate
active
06809615
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a band-pass filter including a plurality of resonators formed on a dielectric plate, and a shared transmitting-and-receiving unit and a communication apparatus using the band-pass filter.
2. Description of the Related Art
One typical planar-circuit dielectric filter is a dielectric filter with attenuation poles at a low- or high-frequency region or both regions of the pass band, as disclosed in Japanese Unexamined Patent Application Publication No. 2000-13106, in which, for coupling resonators that are spaced at least one stage apart from each other, polarization coupling lines are formed on an input/output substrate or a cover which is a portion of a cavity, or otherwise, polarization coupling lines are formed on the upper and lower surfaces of a dielectric plate which is a filter substrate.
FIG. 19
illustrates the structure of a dielectric plate which is a typical filter substrate in the dielectric filter disclosed in the above publication. In
FIG. 19
, electrodes are formed over both surfaces of a rectangular dielectric plate. There are non-electrode portions
4
a
to
4
e
on the upper surface of the dielectric plate. There are also non-electrode portions having the same configuration as that of the non-electrode portions
4
a
to
4
e
formed on the lower surface of the dielectric plate so as to face the non-electrode portions
4
a
to
4
e
. The dielectric portions which are sandwiched between the non-electrode portions formed on the upper and lower surfaces of the dielectric plate serve as resonators. Accordingly, in the example shown in
FIG. 19
, the non-electrode portions or electrode-free portions
4
a
and
4
e
serve as input- and output-stage resonators, and the non-electrode portions or electrode-free portions
4
b
,
4
c
, and
4
d
serve as three resonator stages therebetween. A band-pass filter formed of a total of five resonator stages is thus constructed.
In order to produce an attenuation pole, a polarization line may be formed on a plate different from the dielectric plate shown in FIG.
19
. This plate may be adjacent to the dielectric plate, and the second- and fourth-stage resonators may be magnetically cross-coupled, thereby producing an attenuation pole.
Meanwhile, as demand has increased for more compact, lightweight, and sophisticated electronic devices using such a planar-circuit dielectric filter, such as cellular telephones in particular, the dielectric filter is also required to be more compact and lightweight.
In the example shown in
FIG. 19
, the dielectric plate has an outer dimension of 18×4.8 mm (86.4 mm
2
) where the relative dielectric constant of the dielectric plate is 24 and the center frequency of the pass band is 26.5 GHz. A need still exists for a more compact dielectric plate.
Furthermore, the number of stages of resonators must increase in order to achieve a sharp attenuation characteristic from the pass band to the stop band; this leads to a problem of increased size of the overall device.
A polarization coupling line which is formed in order to produce an attenuation pole may also lead to another problem of conductor loss due to the coupling line, resulting in low Q factor while increasing insertion loss. A separate provision of a substrate which carries a polarization coupling line may also lead to another problem in that any relative misalignment between this substrate and the dielectric plate which is a filter substrate would cause variations in the frequency of the attenuation pole to make the attenuation characteristic unstable, thereby requiring a strategy to overcome this problem.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a compact and lightweight band-pass filter which provides a satisfactory attenuation characteristic from the pass band to the stop band, and a shared transmitting-and-receiving unit and a communication apparatus using the band-pass filter.
To this end, in one aspect of the present invention, a band-pass filter comprising a dielectric filter includes electrodes formed on both upper and lower surfaces of a substantially rectangular dielectric plate, and a plurality of sets of substantially rectangular non-electrode portions which are adjacent to each other, each set of non-electrode portions facing across the dielectric plate, forming resonators in regions confined by the non-electrode portions on the dielectric plate. The resonators other than at least input- and output-stage resonators are n&lgr;/2 resonators, where &lgr; denotes one wavelength and n is an integer more than one, including a group of adjacent resonators which are capacitively coupled, and a group of adjacent resonators which are inductively coupled.
The direction in which the non-electrode portions are aligned differs depending upon whether resonators formed in the portions confined by non-electrode portions on the dielectric plate are capacitively or inductively coupled. The presence of a group of adjacent resonators which are capacitively coupled, and a group of adjacent resonators which are inductively coupled allows the non-electrode portions to be arranged, for example, in a staggered fashion rather than linearly, thereby reducing the rectangular dielectric plate in size in its longitudinal direction. The overall band-pass filter can be therefore more compact and lightweight.
The input-stage resonator may be inductively coupled with the resonator adjacent thereto, and the output-stage resonator may be inductively coupled with the resonator adjacent thereto. The resonators other than the input- and output-stage resonators may be capacitively coupled with each other.
Conversely, the input-stage resonator may be capacitively coupled with the resonator adjacent thereto, and the output-stage resonator may be capacitively coupled with the resonator adjacent thereto. The resonators other than the input- and output-stage resonators may be inductively coupled with each other.
With this structure, the direction in which the input- and output-stage resonators are aligned differs from the direction in which the remaining resonators are aligned, thereby reducing the dielectric plate in size in its longitudinal direction. This structure also provides cross-coupling every other resonator between the input- and output-stage resonators, and the resonators other than the input- and output-stage resonators which are coupled with each other, resulting in polarization.
The resonators other than the input- and output-stage resonators may be &lgr; resonators, where &lgr; denotes one wavelength, and may be arranged so that the longitudinal axes of the resonators are parallel to each other rather than linearly aligned. These resonators may be capacitively coupled with each other when d/L is greater than approximately 0.67, where L denotes the length of the resonators in the longitudinal direction, and d denotes the length of facing portions of adjacent resonators in the resonators.
Conversely, these resonators may be inductively coupled with each other when d/L is smaller than approximately 0.67.
Therefore, a band-pass filter can be constructed merely by defining a relationship between the length L of the resonators in the longitudinal direction and the length d of the facing portions of adjacent resonators, that is, with simplification in design.
In another aspect of the present invention, a band-pass filter comprising a dielectric filter includes electrodes formed on both upper and lower surfaces of a substantially rectangular dielectric plate, and a plurality of sets of substantially rectangular non-electrode portions, each set of non-electrode portions facing across the dielectric plate, forming resonators in regions confined by the non-electrode portions on the dielectric plate. The resonators are arranged so that the electric fields for the resonance mode used by the resonators are oriented in the same direction, and adjacent resonators in the resonators are shifted by a predetermined value in a parallel mann
Hiratsuka Toshiro
Hirose Keiichi
Kanagawa Kiyoshi
Sasaki Yutaka
Sonoda Tomiya
Dickstein , Shapiro, Morin & Oshinsky, LLP
Murata Manufacturing Co. Ltd.
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