Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-02-23
2001-12-04
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S204000, C333S134000
Reexamination Certificate
active
06326866
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bandpass filter, a duplexer using the filter, a high-frequency module using these, and a communications device using the module, more particularly to a bandpass filter used in the rf stage of a microwave band mobile communications apparatus, a duplexer using the filter, a high-frequency module using these, and a communications device using the module.
2. Description of the Related Art
Recently, mobile communications apparatus, especially portable telephones, are being made small-scale and use higher frequencies, and consequently there is increasing demand for a small-scale and narrow-band bandpass filter and duplexer, used in the rf stage and the like of such apparatus.
FIG. 10
shows an electrode pattern of a conventional combine bandpass filter. In
FIG. 10
, a bandpass filter
1
comprises a ground electrode
2
, microstrip line resonators
3
,
4
,
5
and
6
, which are distributed constant line resonators having length of roughly one quarter of the wavelength of the intended frequency, one end of each being an open terminal and the other end connecting to the ground terminal
2
to form a ground terminal, an input terminal
7
and an output terminal
8
. The input terminal
7
and the output terminal
8
are respectively connected to the microstrip line resonators
3
and
6
. Then, the above components are provided on part of one main face of, for instance, a printed substrate, which has a ground terminal provided roughly completely over its other main face, so as to form a bandpass filter. Or, as shown in
FIG. 11
, the above components are provided on a main face of a small dielectric substrate
9
, which has a ground terminal provided roughly completely over its other main face, so as to be used as a single chip component. In
FIG. 11
, like members to
FIG. 10
are designated by like reference characters.
In the bandpass filter
1
of the above constitution, a signal input from the input terminal
7
to the microstrip line resonator
3
is input to a filter circuit comprising the microstrip line resonators
3
,
4
,
5
and
6
. The microstrip line resonators
3
,
4
,
5
and
6
resonate at their intended frequencies, and in addition, they are coupled together by a particularly strong magnetic field generated near their ground terminals, thereby operating as a bandpass filter, allowing only signals close to their intended frequencies to pass and reflecting signals at other frequencies. Then, signals at the intended frequencies are output from the microstrip line resonator
6
to the output terminal
8
.
FIG. 12
shows pass characteristics and reflection characteristics of the bandpass filter
1
. In
FIG. 12
, characteristics a represents insertion loss, characteristic b represents reflection loss, and there is a passband of approximately 400 MHz around 4 GHz.
However, as shown in
FIG. 12
, in the above bandpass filter
1
, the insertion loss characteristic a has an attenuation extreme pl only on the high side. Generally, in a bandpass filter, a large amount of attenuation of insertion loss in regions other than the passband is desirable, but in a normal combine filter either, only one such attenuation extreme is formed or absolutely no attenuation extreme is formed, and consequently it is not possible to obtain a sufficient amount of attenuation in the attenuation regions, which include frequency bands on both sides of the passband. More specifically, as shown in
FIG. 12
, insertion loss of not more than −40 dB (target value AL) at 3.4 GHz is needed on the low side, and insertion loss of not more than −40 dB (target value AH) at 4.6 GHz is needed on the high side, but in fact the insertion loss in each case is only −22 dB and −23 dB respectively.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to solve the problems described above by providing a bandpass filter wherein attenuation extremes can be formed on both sides of the passband, a duplexer using the bandpass filter, a high-frequency module using these, and a communications device using the high-frequency module.
In order to achieve the above-mentioned objects, the bandpass filter of the present invention provides a combine bandpass filter, comprising a plurality of distributed constant line resonators, one end of each being an open terminal and the other end a ground terminal, provided in a row, wherein the open terminals are disposed outline the distributed constant line resonators and project further than the inner distributed constant line resonators.
Furthermore, according to the bandpass filter of the present invention, the open terminals of the inner distributed constant line resonators are close together.
Furthermore, according to the bandpass filter of the present invention, a ground electrode is provided close to the open terminals of the distributed constant line resonators, and capacitance is formed between the open terminals of the distributed constant line resonators and the ground electrode.
Furthermore, according to a duplexer of the present invention, two of any of the bandpass filters described above are connected.
Furthermore, a high-frequency module of the present invention uses any one of the above bandpass filters or the duplexer.
Furthermore, a communications device of the present invention uses the above high-frequency module.
By such a constitution, the bandpass filter of the present invention is able to provide attenuation extremes on both sides of the passband.
Furthermore, the duplexer of the present invention can be made small-scale.
Furthermore, in the high-frequency module of the present invention, circuit constitution can easily be made small-scale and cost reduced.
Furthermore, the communications device of the present invention can be made small-scale and cost reduced.
REFERENCES:
patent: 4168479 (1979-09-01), Rubin
patent: 5004992 (1991-04-01), Grieco et al.
patent: 5376908 (1994-12-01), Kawaguchi et al.
patent: 5977847 (1999-11-01), Takahashi
patent: 5986525 (1999-11-01), Sasaki et al.
Patent Abstracts of Japan, vol. 7, No. 182 (E192), Aug. 11, 1983 & JP 58 085601 A (Nippon Denki KK), May 23, 1983, abstract.
Patent Abstracts of Japan, vol. 1, No. 156 (E-74), Dec. 13, 1977 & JP 52 099750 A (Toshiba Corp), Aug. 22, 1977, abstract.
Patent Abstracts of Japan, vol. 11, No. 367 (E-561), Nov. 28, 1977 & JP 62 140501 A (NEC Corp), Jun. 24, 1987, abstract.
Patent Abstracts of Japan, vol. 7, No. 76 (E-561), Nov. 28, 1987 & JP 58 005001 A (Matsushita Denki Sangyo KK), Jan. 12, 1983, abstract.
Patent Abstracts of Japan, vol. 15, No. 498 (E-1146), Dec. 17, 1991 & JP 03 218102 A (Fujitsu General Ltd) Sep. 25, 1991, abstract.
Sasaki Yutaka
Tanaka Hiroaki
Lee Benny
Murata Manufacturing Co. Ltd.
Nguyen Patricia
Ostrolenk Faber Gerb & Soffen, LLP
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