Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1999-12-01
2002-04-16
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S193000
Reexamination Certificate
active
06373350
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a branching filter useful in a compact communication device such as a portable telephone set.
Compact, lightweight portable telephone sets and other portable communication equipment have been undergoing intensive development in recent years. Small, high-performance components are required. The branching filter, which is used as a radio-frequency (RF) filter in such equipment, is one of these components. Incidentally, a branching filter is also referred to as an antenna duplexer.
FIG. 1
is a schematic diagram of a first conventional branching filter, comprising an antenna port
1
, inductors
2
,
3
,
4
, a transmitting (TX) filter
5
, a receiving (RX) filter
6
, a transmitting port
7
, and a receiving port
8
. The transmitting filter
5
and receiving filter
6
employ dielectric resonators.
FIG. 2
is a perspective view of this branching filter, showing the substrate
9
on which the transmitting filter
5
and receiving filter
6
are mounted.
FIG. 3
is a perspective view of the underside of the substrate
9
, showing the metalized pattern
9
a
from which the inductors
2
,
3
,
4
are formed, and the insulating pattern
9
b
in which the surface of the substrate
9
is exposed.
This first conventional branching filter has good isolation characteristics, because the transmitting filter
5
and receiving filter
6
are mounted separately, but it requires a comparatively large substrate
9
with special patterning to form the inductors
2
,
3
,
4
. There are also problems of mutual interference between interconnecting lines and inadequate separation between the transmitting frequency band and receiving frequency band. A compact, high-performance filter is difficult to achieve with this design.
Surface-acoustic-wave (SAW) filters of the resonator type provide a way to achieve a more compact branching-filter configuration.
FIG. 4
shows a second conventional branching filter housed in a single package
10
. The interior
11
A of the package includes a ground plane
11
B, an impedance-matching element
12
, a phase-matching element
13
, and a trap circuit
14
, as well as a transmitting SAW-filter element
15
and a receiving SAW-filter element
16
, as described in Japanese Unexamined Patent Application 06097761.
Placing all of the elements of the second conventional branching filter in a single package, however, leads to the problems noted above: mutual interference between interconnecting lines, and inadequate separation between the transmitting and receiving frequency bands.
In the first conventional branching filter, the transmitting filter
5
and receiving filter
6
are sealed in separate packages, but as noted above, the inductors
2
,
3
,
4
are formed on the substrate
9
, increasing the space occupied by the substrate
9
and precluding the design of a very compact branching filter. Furthermore, the basic filter design in
FIG. 1
leads to the above-mentioned problems of mutual interference between interconnecting lines and inadequate separation between the transmitting and receiving frequency bands. The second conventional branching filter in
FIG. 4
, which employs SAW resonators, also exhibits the same problems of mutual interference between interconnecting lines and inadequate separation between the transmitting and receiving frequency bands.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a compact, high-performance branching filter.
According to the present invention, a branching filter comprises a first package and a second package. The first package encloses a transmitting filter of the SAW-resonator type. The second package encloses a receiving filter of the SAW-resonator type. The transmitting filter and receiving filter have different passbands. Other necessary elements, such as striplines having a certain length, are incorporated into the first and second packages.
REFERENCES:
patent: 2-29109 (1990-01-01), None
patent: 6-6170 (1994-01-01), None
patent: 06097761 (1994-04-01), None
patent: 7-38376 (1995-02-01), None
patent: 07226607 (1995-08-01), None
patent: 8-84045 (1996-03-01), None
patent: 08191230 (1996-07-01), None
patent: 09181567 (1997-07-01), None
patent: 10270976 (1998-10-01), None
patent: 11-17495 (1999-01-01), None
Frank Robert J.
Oki Electric Industry Co. Ltd.
Pascal Robert
Sartori Michael A.
Summons Barbara
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