Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1999-08-24
2001-10-16
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S204000, C333S219000
Reexamination Certificate
active
06304156
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a dielectric antenna duplexer and a dielectric filter used mainly in high frequency radio devices such as mobile telephones. An antenna duplexer is a device for sharing one antenna by a transmitter and a receiver, and it is composed of a transmission filter and a reception filter. The invention is particularly directed to a laminated dielectric antenna duplexer having a laminate structure by laminating a dielectric sheet and an electrode layer and baking into one body. It also related to a laminated dielectric filter. The invention is further directed to a block type dielectric filter applying a circuit construction of the laminated dielectric filter of the invention into a conventional dielectric block structure.
BACKGROUND OF THE INVENTION
Along with the advancement of mobile communications, recently, the antenna duplexer is used widely in many hand-held telephones and car-mounted telephones. An example of a conventional antenna duplexer is described below with reference to a drawing.
FIG. 46
is a perspective exploded view of a conventional antenna duplexer. In
FIG. 46
, reference numerals
701
to
706
are dielectric coaxial resonators,
707
is a coupling substrate,
708
is a metallic case,
709
is a metallic cover,
710
to
712
are series capacitors,
713
and
714
are inductors,
715
to
718
are coupling capacitors,
721
to
726
are coupling pins,
731
is a transmission terminal,
732
is an antenna terminal,
733
is a reception terminal, and
741
to
747
are electrode patterns formed on the coupling substrate
707
.
The dielectric coaxial resonators
701
,
702
,
703
, series capacitors
710
,
711
,
712
, and inductors
713
,
714
are combined to form a transmission band elimination filter. The dielectric coaxial resonators
704
,
705
,
706
, and coupling capacitors
715
,
716
,
717
,
718
compose a reception band pass filter.
One end of the transmission filter is connected to a transmission terminal which is electrically connected with a transmitter, and the other end of the transmission filter is connected to one end of a reception filter, and is also connected to an antenna terminal electrically connected to the antenna. The other end of the reception filter is connected to a reception terminal which is electrically connected to a receiver.
The operation of an antenna duplexeris described below. First of all, the transmission band elimination filter shows a small insertion loss to the transmission signal in the transmission frequency band, and can transmit the transmission signal from the transmission terminal to the antenna terminal while hardly attenuating it. By contrast, it shows a larger insertion loss to the reception signal in the reception frequency band, and reflects almost all input signal in the reception frequency band, and therefore the reception signal entering from the antenna terminal returns to the reception band pass filter.
On the other hand, the reception band filter shows a small insertion loss to the reception signal in the reception frequency band, and transmits the reception signal from the antenna terminal to the reception terminal while hardly attenuating it. The transmission signal in the transmission frequency band shows a large insertion loss, and reflects almost all input signal in the transmission frequency band, so that the transmission signals coming from the transmission filter is sent out to the antenna terminal.
In this design, however, in manufacturing dielectric coaxial resonators, there is a limitation in fine processing of ceramics, and hence it is hard to reduce its size. Downsizing is also difficult because many parts are used such as capacitors and inductors, and another problem is the difficulty in lowering the assembling cost.
The dielectric filter is a constituent element of the antenna duplexer, and is also used widely as an independent filter in mobile telephones and radio devices, and there is a demand that they be smaller in size and higher in performance. Referring now to a different drawing, an example of a conventional block type dielectric filter possessing a different constitution from the above described structure is described below.
FIG. 47
is a perspective oblique view of a block type dielectric filter of the prior art. In
FIG. 47
, reference numeral
1200
is a dielectric block,
1201
to
1204
are penetration holes, and
1211
to
1214
, and
1221
,
1222
,
1230
are electrodes. The dielectric block
1200
is entirely covered with electrodes, including the surface of the penetration holes
1201
to
1204
, except for peripheral parts of the electrodes on the surface of which the electrodes
1221
,
1222
and others are formed.
The operation of the thus constituted dielectric filter is described below. The surface electrodes in the penetration holes
1201
to
1204
serve as the resonator, and the electrode
1230
serves as the shield electrode. The electrodes
1211
to
1214
are to lower the resonance frequency of the resonator composed of the electrodes in the penetration holes, and functions as the loading capacity electrode. By nature, a ¼ wavelength front end short-circuit transmission line is not coupled at the resonance frequency and shows a band stop characteristic, but by thus lowering the resonance frequency, an electromagnetic field coupling between transmission lines occurs in the filter passing band, so that a band pass filter is created. The electrodes
1221
,
1222
are input and output coupling capacity electrodes, and input and output coupling is effected by the capacity between these electrodes and the resonator, and the loading capacity electrode.
The operating principle of this filter is a modified version of a comb-line filter disclosed in the literature (for example, G. L. Matthaei, “Comb-Line Band-pass Filters of Narrow or Moderate Bandwidth”; the Microwave Journal, August 1963). The block type filter in this design is a comb-line filter composed of a dielectric ceramic (for example, see U.S. Pat. No. 4,431,977). The comb-line filter always requires a loading capacity for lowering the resonance frequency in order to realize the band pass characteristic.
FIG. 48
shows the transmission characteristic of the comb-line type dielectric filter in the prior art. The transmission characteristic shows the Chebyshev characteristic increasing steadily as the attenuation outside the bandwidth departs from the center frequency.
In this construction, however, it is not possible to realize the elliptical function characteristic possessing the attenuation pole near the bandwidth of the transmission characteristic, and hence the range of selection is not sufficient for filter performance.
Also, in such dielectric filter, for smaller and thinner constitution, the flat type laminate dielectric filter that can be made thinner than the coaxial type is expected henceforth, and several attempts have been made to design such a device. A conventional example of a laminated dielectric filter is described below. The following explanation relates to a laminated “LC filter” (trade mark) that is put into practical use as a laminated dielectric filter by forming lumped element type capacitors and inductors in a laminate structure.
FIG. 49
is a perspective exploded view showing the structure of a conventional laminate “LC filter”. In
FIG. 49
, reference numerals
1
and
2
are thick dielectric layers. On a dielectric sheet
3
are formed inductor electrodes
3
a
,
3
b
, and capacitor electrodes
4
a
,
4
b
are formed on a dielectric sheet
4
, capacitor electrodes
5
a
,
5
b
on a dielectric sheet
5
, and shield electrodes
7
a
,
7
b
on a dielectric sheet
7
. By stacking up all these dielectric layers and dielectric sheets together with a dielectric sheet
6
for protecting the electrodes, an entirely laminated structure is formed.
The operation of the thus constituted dielectric filter is described below. First, the confronting capacitor electrodes
4
a
and
5
a
, and
4
b
and
5
b
respectively compose parallel plate
Aizawa Kimio
Fujino Takashi
Ishizaki Toshio
Kushitani Hiroshi
Nakakubo Hideaki
Pascal Robert
Summons Barbara
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