Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-11-12
2001-08-28
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000, C333S134000
Reexamination Certificate
active
06281768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric filter, a duplexer, and a communication apparatus incorporating the same, which are used in a high-frequency circuit.
2. Description of the Related Art
Dielectric filters having both band-pass characteristics and band-stop characteristics obtained by a plurality of resonant lines disposed in a dielectric block are disclosed in (1) Japanese Unexamined Patent Publication No. 8-32313 and (2) Japanese Unexamined Patent Publication No. 8-330806. In each of the dielectric filters, the plurality of resonant lines are combline-coupled in the dielectric block to obtain band-pass characteristics, and in addition, there is provide a trap resonator to form an attenuation pole.
FIGS. 10A
to
10
D show an example of a duplexer using the conventional art.
FIGS. 10A
to
10
D are projection views of the duplexer, in which
FIG. 10A
is a front view,
FIG. 10B
is a left side view,
FIG. 10C
is a right side view, and
FIG. 10D
is a top view.
In this duplexer, holes and electrodes are formed with respect to a rectangular-parallelepiped dielectric block
1
. Reference numerals
2
(
2
a,
2
b,
and
2
c
),
3
,
4
, (
4
a,
4
b,
4
c,
and
4
d
), and
5
denote resonant-line holes, inside of which inner conductors are disposed to form resonant lines. Reference numerals
7
,
8
, and
9
denote excitation-line holes, inside of which inner conductors are disposed to form excitation lines. Reference numerals L
1
, L
2
to Ld shown in the figure indicate serial numbers given to the above-mentioned lines in order to be referred to in an equivalent circuit shown below.
FIG. 11
is an equivalent circuit diagram of the duplexer shown in FIG.
10
. In this figure, since Z
12
acts a phase circuit of &pgr;/2 [rad] (hereinafter indicated by omitting the rad as a unit of a phase angle), (Z
1
and Z
12
) act as trap resonators. Z
3
, Z
4
, and Z
5
act as a three-stage resonator in which they are combline-coupled in sequence. Similarly, Z
7
, Z
8
, Z
9
, and Za act as a four-stage resonator in which they are combline-coupled in sequence. Additionally, since Zbc acts as a &pgr;/2 phase circuit, (Zc and Zbc) act as trap resonators.
FIG. 12
shows the pass characteristics of the duplexer described above. In this figure, the upper graph shows the pass characteristics of a reception filter, and the lower graph shows those of a transmitting filter. In the reception filter, signals of the receiving frequency band are allowed to pass through, whereas signals of the transmitting frequency band are attenuated, and in the transmitting filter, signals of the transmitting frequency band are allowed to pass through, whereas signals of the receiving frequency band are attenuated.
However, in the dielectric filters in accordance with the conventional art described in (1) and (2), although attenuation characteristics can be obtained by a polarity generated due to the coupling circuit of combline coupling and the single trap resonator, the depth (the amount of attenuation) of the polarity obtained by the coupling circuit cannot be changed. In addition, in order to bring the position of the polarity close to a pass band, it is necessary to narrow the pitch between the resonators (the distance between the resonant-line holes). However, if it is narrowed, Qo of the resonators is deteriorated.
Furthermore, in the dielectric filter according to the conventional art, the initial-stage or final-stage resonant line of the resonant lines being combline-coupled is coupled to the excitation line to obtain an external coupling, and the trap-resonator resonant line is adjacent to the excitation line, with the result that only a single attenuation pole can be obtained by the trap resonator.
SUMMARY OF THE INVENTION
To overcome the above described problems, one preferred embodiments of the present invention provides a dielectric filter comprising: a plurality of resonant lines disposed in a dielectric block, in a dielectric substrate, or on a dielectric substrate; wherein the open ends of at least one adjacent pair of the resonant lines are oriented in the same direction to be combline-coupled, a first trap-resonator resonant line and a signal inputting/outputting excitation line are each interdigitally coupled to one of the plurality of resonant lines, and a second trap-resonator resonant line is interdigitally coupled to the excitation line.
In this way, the adjacent specified ones of the plurality of resonant lines disposed in the dielectric block, the dielectric substrate, or on the dielectric substrate are combline-coupled, and at the part of the combline-coupling, band-pass filter characteristics are generated. In addition, the one of the plurality of resonant lines and the first trap-resonator resonant line are interdigitally coupled to produce a first attenuation pole, and the signal inputting/outputting excitation line and the second trap-resonator resonant line are interdigitally coupled to produce a second attenuation pole. Producing the first and second attenuation poles permits signals of a relatively wide frequency band to be largely attenuated, which leads to great improvement in the attenuation characteristics of the low-frequency side or high-frequency side in the pass band. In addition, since there is no influence of the pitch between resonators, widening the pitch between resonators can increase Qo, which leads to sufficient suppression of the insertion losses in the pass band.
Another preferred embodiment of the present invention provides a duplexer comprising a transmitting filter and a reception filter constituted of a plurality of resonant lines disposed in a dielectric block, in a dielectric substrate, or on a dielectric substrate, at least one adjacent pair of the resonant lines being mutually coupled, wherein trap-resonator resonant lines are disposed to be interdigitally coupled to the final-stage resonant line of the reception filter and an excitation line coupled thereto or the initial-stage resonant line of the transmitting filter and an excitation line coupled thereto.
In this arrangement, the trap-resonator resonant lines for being interdigitally coupled to both the final-stage resonant line of the reception filter and the excitation line coupled to the resonant line are disposed so as to obtain reception filter characteristics having attenuation poles produced by the two trap-resonator resonant lines. In addition, the trap-resonator resonant lines for being each interdigitally coupled to both the initial-stage resonant line of the transmitting filter and the excitation line coupled to the resonant line are disposed so as to obtain transmitting-filter characteristics having attenuation poles produced by the two trap-resonator resonant lines. This permits the characteristics of the reception filter significantly attenuating the signals of the transmitting-frequency band to be easily obtained, and also permits the transmitting filter significantly attenuating the signals of the receiving-frequency band to be easily obtained.
That is, a duplexer can be produced where one of the transmitting filter and the reception filter or both of them having characteristics which significantly attenuate the frequency band of the counterpart filter.
Yet another preferred embodiment of the invention provides a communication apparatus by forming the dielectric filter or the duplexer described above in a high-frequency circuit section.
Using a compact filter or duplexer capable of passing the signals of a desired frequency band with low insertion losses to greatly attenuate the signals of the stopping frequency band permits a compact communication apparatus having an excellent high-frequency circuit characteristic to be produced.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
REFERENCES:
patent: 4757284 (1988-07-01), Ueno
patent: 6147575 (2000-11-01), Hirstauka et al.
Hiroshima Motoharu
Kato Hideyuki
Tada Hitoshi
Murata Manufacturing Co. Ltd.
Nguyen Patricia T.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
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