Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2003-01-08
2004-06-08
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S204000
Reexamination Certificate
active
06747528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a small dielectric filter used for a high frequency radio appliance such as a portable telephone, etc., a dielectric filter which has strip line type resonator electrodes on a dielectric substrate, and connects them in electromagnetic field, a antenna duplexer, etc.
2. Related Art of the Invention
Recently, dielectric filters have been widely used as high frequency filters of portable telephones, etc., and have been requested to be smaller and thinner. Under the situation, a laminated dielectric filter which can be thinner than a coaxial type filter is expected to have a higher market share.
An example of the conventional laminated dielectric filter is described below by referring to the attached drawings.
FIG. 32
is an analytic oblique view of the structure of a conventional dielectric filter.
FIG. 33
shows an equivalent circuit of the dielectric filter shown in FIG.
32
.
In
FIG. 32
, the dielectric filter is a structure including: dielectric layers
3401
,
3402
,
3403
,
3404
, and
3405
; resonator electrodes
3406
a
and
3406
b
, transmission line electrodes
3407
a
,
2307
b
, and
3407
c
having input/output terminals on both ends; notch capacity electrodes
3408
a
and
3408
b
: and shield electrodes
3409
and
3410
. These internal electrodes are formed between each dielectric layers.
As shown in
FIG. 33
, the dielectric filter forming the band rejection characteristic around the resonance frequency of the resonator includes resonators
3501
a
and
3501
b
, and transmission lines
3502
a
,
3502
b
, and
3502
c
connected through capacitors
3503
a
and
3503
b
. The capacitors
3503
a
and
3503
b
are respectively connected in series to the resonators
3501
a
and
3501
b
. Therefore, they functions as attenuation poles indicating high attenuation amounts around the resonance frequency of the resonators
3501
a
and
3501
b.
Normally, in the filter theory, the line length of the transmission line
3502
c
is set equal to ¼ of the wavelength corresponding the resonance frequency of the resonators
3501
a
and
3501
b
so that a filter can be configured with the infinite impedance of the transmission line electrode
3502
c
, and the band rejection characteristic formed around the resonance frequency of the resonators
3501
a
and
3501
b.
FIG. 34
also shows an equivalent circuit of a filter forming a band rejection characteristic around the resonance frequency of a resonator. As shown in
FIG. 34
, the filter forming a band rejection characteristic around the resonance frequency of a resonator includes a transmission line having input/output terminals at both ends, a capacitor, and a resonator. A transmission line
4501
is connected to a resonator
4503
through a capacitor
4502
.
Since the capacitor
4502
is serially connected to the resonator
4503
, it functions as an attenuation pole indicating a high attenuation amount around the resonance frequency of the resonator
4503
. In common filter designing, it is normal that input/output terminals at both ends have the same impedance values. Therefore, the values of elements forming a filter circuit are symmetrically designed.
However, to actually realize the configuration as shown in
FIG. 32
as a dielectric filter, the long line of the transmission line electrode, which is a primary line of the filter, does not allow the transmission line having the length of ¼ of the wavelength corresponding to the resonance frequency of the resonator to function as is on a dielectric layer which has a finite space. Therefore, wiring pattern of the transmission line can't be formed straight, that is, the pattern becomes inevitably zigzag, and the width of the transmission line is reduced so that it can be designed on a dielectric layer or in a dielectric. The above mentioned configuration of a transmission line has the problem that it incurs the deterioration due to a loss in the pass band frequency of a dielectric filter forming the band rejection characteristic around the resonance frequency of the resonator.
With the configuration shown in
FIG. 34
, a filter forming a band rejection characteristic around the resonance frequency of a resonator can include attenuation poles equal in number to the resonators forming the filter. However, when the values of attenuation pole forming capacitors are equal, the positions of the plurality of attenuation poles are the same. Therefore, as shown in
FIG. 36
, there has been the problem that the rejection band is necessarily narrow.
FIG. 35
is a Smith chart showing the state. Furthermore, when the above mentioned filter is used for one or both of the transmission filter and the reception filter of an antenna duplexer, the terminals connected at both ends of the transmission lines have different impedance values. Therefore, when the above mentioned filter is used for a antenna duplexer, there has been the problem that a filter characteristic has distortion, etc.
SUMMARY OF THE INVENTION
The present invention has been developed to solve the above mentioned problem, and aims at providing a small and thin laminated dielectric filter forming a band rejection characteristic around the resonance frequency of a resonator, and having a low loss characteristic at a desired frequency.
Furthermore, the present invention aims at realizing a filter having an excellent band rejection characteristic around the resonance frequency of a resonator with a simple configuration, and providing a filter having an excellent characteristic as a transmission filter and a reception filter of a antenna duplexer.
The 1
st
invention of the present invention is a dielectric filter, comprising:
a plurality of resonators; and
at least one transmission line provided among said plurality of resonators,
wherein a band rejection characteristic is formed around a resonance frequency of said resonator, and a line length of said transmission line is shorter than ¼ of a wavelength corresponding to the resonance frequency of said resonator.
The 2
nd
invention of the present invention is the dielectric filter according to 1
st
invention, wherein said plurality of resonators are coupled in electromagnetic field.
The 3
rd
invention of the present invention is the dielectric filter according to 2
nd
invention, wherein:
a dielectric sheet and an electrode layer are layered and co-fired into one layered structure; and
said resonator and said transmission line are realized as an entire or a part of said electrode layer.
The 4
th
invention of the present invention is the dielectric filter according to 3
rd
invention, wherein
said dielectric sheet comprises at least one dielectric layer;
said electrode layer comprises:
a plurality of resonator electrodes provided on one primary surface of said dielectric layer; and
a transmission line electrode, provided on another primary surface of said dielectric layer, whose ends are input/output terminals;
said resonator electrode operates as said resonator; and
in a projection drawing where said resonator electrode and said transmission line electrode are viewing from a direction perpendicular to a surface of said dielectric layer, there are a plurality of overlapping portions of said transmission line electrode and adjacent said resonator electrodes, such portion of said transmission electrode that is positioned between each central point of said overlapping portions, corresponds to said transmission line, and a part of said transmission line electrode is positioned along central points of an overlapping portion of said resonator electrodes and said transmission line electrode, and corresponds to said transmission line.
The 5
th
invention of the present invention is the dielectric filter according to 3
rd
invention, wherein
said dielectric sheet comprises at least five dielectric layers from a first dielectric layer to a fifth dielectric layer;
said electrode layer comprises at least:
a first shield electrode, provided between said first dielectric layer and said s
Ishizaki Toshio
Kushitani Hiroshi
Maekawa Tomoya
Nakakubo Hideaki
Shigemura Hiroshi
Chang Joseph
Matsushita Electric - Industrial Co., Ltd.
Pascal Robert
Smith , Gambrell & Russell, LLP
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