Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-08-04
2004-02-24
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S204000
Reexamination Certificate
active
06696903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a filter, particularly a laminated dielectric filter, which mainly is used in high-frequency radio equipment such as portable telephones.
BACKGROUND OF THE INVENTION
Recently, with reduction in size of communication equipment, laminated dielectric filters effective for size reduction are used commonly as high-frequency filters. One example of conventional laminated dielectric filters is described with reference to drawings as follows.
FIG. 4
shows an exploded perspective view of a conventional laminated dielectric filter. The conventional laminated dielectric filter shown in
FIG. 4
includes dielectric layers
301
, shield electrodes
302
a
and
302
b
, resonator electrodes
303
a
,
303
b
, and
303
c
, capacitor electrodes
304
a
,
304
b
,
305
a
,
305
b
,
307
a
,
307
b
, and
307
c
, and side electrodes
308
a
,
308
b
,
308
c
,
308
d
,
309
a
, and
309
b
. In the dielectric layers
301
, the shield electrode
302
a
, the resonator electrodes
303
a
,
303
b
, and
303
c
, the capacitor electrodes
304
a
,
304
b
,
305
a
,
305
b
,
307
a
,
307
b
, and
307
c
, and the shield electrode
302
b
are positioned sequentially. In addition, the side electrodes
308
a
and
308
b
on the left and right side faces of the dielectric body connect the shield electrodes
302
a
and
302
b
to form ground terminals. The side electrode
308
c
on the back face of the dielectric body connects the shield electrodes
302
a
and
302
b
and a common short-circuit end of the resonator electrodes
303
a
,
303
b
, and
303
c
to form a ground terminal. The side electrodes
308
d
on the front face of the dielectric body connect the capacitor electrodes
307
a
,
307
b
, and
307
c
corresponding to the open ends of the resonator electrodes
303
a
,
303
b
, and
303
c
, respectively. The side electrodes
309
a
and
309
b
on the left and right side faces of the dielectric body are connected to the capacitor electrodes
304
a
and
304
b
to form input/output terminals.
The structural view of the laminated dielectric filter thus configured is shown in
FIGS. 5A and 5B
.
FIG. 5A
is its left side view and
FIG. 5B
its front view.
FIGS. 5A and 5B
also show schematic capacitors formed between electrodes formed on an upper surface of a dielectric layer and electrodes formed on an upper surface of another dielectric layer, which oppose each other, respectively.
An equivalent circuit of the conventional laminated dielectric filter shown in
FIGS. 4
,
5
A and
5
B can be illustrated as shown in FIG.
6
. The resonator electrodes
303
a
,
303
b
, and
303
c
form front end short-circuit ¼ wavelength resonators R
303
a
, R
303
b
, and R
303
c
as shown in FIG.
6
. The open ends of the resonators R
303
a
, R
303
b
, and R
303
c
are connected to the ground terminals via the loading capacitor elements C
307
a
, C
307
b
, and C
307
c
, respectively. The open ends of the resonators R
303
a
and R
303
b
are connected to each other via an inter-stage coupling capacitor element C
305
a
and the open ends of the resonators R
303
b
and R
303
c
via an inter-stage coupling capacitor element C
305
b
. Furthermore, the resonators R
303
a
and R
303
c
on the outer sides are connected to the input/output terminals via input/output coupling capacitor elements C
304
a
and C
304
b
, respectively.
Therefore, the laminated dielectric filter shown in
FIG. 4
functions as a bandpass filter with the one ends of the capacitor elements C
304
a
and C
304
b
serving as the input/output ends. In addition, two attenuation poles are formed by a parallel resonance circuit formed of the inter-stage coupling capacitors C
305
a
and C
305
b
and magnetic-field couplings
401
a
and
401
b
occurring between the resonators R
303
a
and R
303
b
and between the resonators R
303
b
and R
303
c
. The frequencies of the attenuation poles depend on inter-stage coupling capacitance and the magnitude of the magnetic-field couplings, i.e. resonant gaps.
In the configuration as described above, however, the resonators R
303
a
and R
303
c
on the both sides bypass the resonator R
303
b
positioned at the center to be coupled directly to each other by a magnetic-field coupling as indicated with the numeral
401
c
. Therefore, frequency characteristics of the two attenuation poles vary and thus the characteristics as designed cannot be obtained. The magnetic-field coupling
401
c
is determined uniquely when the magnetic-field couplings
401
a
and
401
b
are determined, i.e. when the resonant gaps are determined. Consequently, the two attenuation poles cannot be controlled freely while consideration is given to the magnetic-field coupling
401
c.
SUMMARY OF THE INVENTION
The present invention is intended to provide a filter, particularly a laminated dielectric filter, allowing attenuation poles outside a passband to be controlled freely.
In one embodiment, a filter of the present invention includes a plurality of resonators coupled to one another by electromagnetic-field coupling. In the embodiment, non-adjacent resonators are electrically coupled to each other with a series circuit formed of a capacitor and a transmission line.
According to the filter of this embodiment, the capacitor formed between the non-adjacent resonators is regulated without being affected by the magnetic-field bypass coupling between the non-adjacent resonators. Thus, attenuation poles outside a passband can be controlled freely.
In the above-mentioned filter, it is preferred to electrically couple adjacent resonators to each other with a series circuit of a capacitor and a transmission line.
According to this configuration, it is possible to control at least two attenuation poles of a parallel resonance circuit formed by the electromagnetic coupling and capacitive coupling between adjacent resonators.
In the above-mentioned filter, it is preferable that the plurality of resonators and the transmission line are formed inside a dielectric body.
According to this configuration, the capacitor as a component of the filter can be formed easily by using the plurality of resonators and the transmission line as electrodes.
In another embodiment, a dielectric filter of the present invention includes a plurality of shield electrodes formed on outer faces of a dielectric body, resonator electrodes formed of at least three front end short-circuit ¼ wavelength transmission lines, a plurality of first transmission line electrodes, each of which has portions opposing respective portions of two adjacent resonator electrodes included in the resonator electrodes, and second transmission line electrodes having portions opposing the plurality of first transmission electrodes, respectively. The resonator electrodes, the first transmission line electrodes, and the second transmission line electrodes are formed between the plurality of shield electrodes.
In some embodiments, inter-stage coupling capacitors are formed between adjacent resonator electrodes and the first transmission line electrodes opposing them, and bypass capacitors are formed between the first transmission line electrodes and the second transmission line electrodes opposing them. Due to the bypass circuit formed of a series circuit including the bypass capacitors and the second transmission line electrodes, the attenuation poles outside the passband can be controlled freely by the adjustment of capacitance of the inter-stage coupling capacitors without being affected by a magnetic-field bypass coupling between non-adjacent resonator electrodes. Thus, a capacitive coupling type bandpass filter having the above-mentioned effect of controlling the attenuation freely can be obtained.
In the dielectric filter, it is preferable that the plurality of shield electrodes are connected to one another, and then are grounded.
According to this configuration, between the shield electrodes thus grounded, filter components can be positioned. Therefore, without being affected by an external electromagnetic field, desired filter characteristics ca
Kawahara Emiko
Kushitani Hiroshi
Nakakubo Hideaki
Yamada Toru
Jones Stephen E.
Matsushita Electric - Industrial Co., Ltd.
Pascal Robert
Rosenthal & Osha L.L.P.
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