Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
2000-09-14
2001-07-17
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S202000, C333S219000, C333S134000
Reexamination Certificate
active
06262640
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coplanar line filter and duplexer, more particularly to a coplanar line filter and duplexer for use in a microwave band communications device and the like.
2. Description of the Related Art
In recent years, a bandpass filter using a coplanar resonator has been proposed as a filter in a microwave band communications device. For instance,
FIG. 10
shows a bandpass filter
81
comprising &lgr;/4 coplanar resonators Q
11
~Q
13
are connected in series. The &lgr;/4 coplanar resonators Q
11
~Q
13
are connected between input and output terminals
87
and
88
via capacitors C
11
~C
14
, comprising lumped constant elements. The &lgr;/4 coplanar resonator Q
11
comprises a center conductor
82
a
and a ground conductor
83
, provided while ensuring a gap from the center conductor
82
a
. One end of the center conductor
82
a
is electrically connected to the ground conductor
83
, forming a &lgr;/4 coplanar resonator Q
11
with one connected end. Similarly, the &lgr;/4 coplanar resonators Q
12
and Q
13
comprise center conductors
82
b
and
82
c
, having electrical length corresponding to a quarter wavelength, and the ground conductor
83
, provided while ensuring a gap from these center conductors
82
b
and
82
c.
Furthermore, the bandpass filter
91
shown in
FIG. 11
comprises &lgr;/2 coplanar resonators Q
14
~Q
16
connected in series. The &lgr;/4 coplanar resonator Q
14
comprises a center conductor
92
a
, having electrical length corresponding to a half wavelength, and ground conductors
93
, provided on either side of the center conductor
92
a
while ensuring a gap between the center conductor
92
a
and the ground conductors
93
. Similarly, the &lgr;/2 coplanar resonators Q
15
and Q
16
each comprise center-conductors
92
b
and
92
c
, having electrical lengths corresponding to a half wavelength, and the ground conductors
93
, on either side of the center conductors
92
b
and
92
c
while ensuring a gap between these and the ground conductors
93
. The &lgr;/2 coplanar resonators Q
14
~Q
16
are connected in series by capacitive couplers C
16
and C
17
, formed at a gap provided between center conductors
92
a
and
92
b
and a gap provided between center conductors
92
b
and
92
c
, and are connected between input/output terminals
97
and
98
by capacitive couplers C
15
and C
18
, formed at a gap provided between the center conductor of the input/output terminal
97
and the center conductor
92
a
of the resonator Q
14
, and a gap provided between the center conductor of the input/output terminal
98
and the center conductor of the resonator Q
16
.
However, in the bandpass filter
81
shown in
FIG. 10
, since the center conductors
82
a
~
82
c
of the &lgr;/4 coplanar resonators Q
11
~Q
13
are mutually separated by the ground conductor
83
, it is difficult to connect the &lgr;/4 coplanar resonators Q
11
~Q
13
with a distribution-constant device, and design was complex. On the other hand, since the bandpass filter
91
shown in
FIG. 11
, uses center conductors
92
a
~
92
c
having electrical lengths corresponding to a half wavelength, it is large-scale by comparison with a bandpass filter which used &lgr;/4 coplanar resonators.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention provide an easily-designed small-scale coplanar line filter and duplexer.
One preferred embodiment of the present invention provides a coplanar line filter or a duplexer, comprising: a dielectric substrate; a plurality of &lgr;/4 coplanar resonators provided on said dielectric substrate, said plurality of &lgr;/4 coplanar resonators comprising; a first center conductor having electrical length corresponding to a quarter wavelength; and a ground conductor provided with a gap from said first center conductor; a capacitive coupling portion comprising a gap provided between said first center conductors of a pair of said &lgr;/4 coplanar resonators; and a inductive coupling portion, comprising a guide conductor which electrically connects said first center conductor and ground, provided at a joint portion of a pair of said &lgr;/4 coplanar resonators: said plurality of &lgr;/4 coplanar resonators being connected in series with said capacitive coupling portion and said inductive coupling portion provided alternately.
By the above described structure and arrangement, a coplanar line filter or a duplexer can be made small-scale by using coplanar resonators comprising a center conductor having electrical length corresponding to a quarter wavelength. Capacitive couplers, using capacitance in a gap provided between center conductors of multiple &lgr;/4 coplanar resonators, and dielectric couplers, using inductance of guide conductors electrically connecting center conductors and ground conductors, are alternately repeated and connected in series. With this arrangement, the capacitive coupling is strengthened when the capacitance of the gap between center conductors is stronger, and the inductive coupling is strengthened when the inductance of the guide conductors, electrically connecting the center conductors and ground conductors, is stronger. Therefore, the bandwidth of the filter or the duplexer is set by adjusting the strength and weakness of these distribution-constant capacitive couplers and dielectric couplers.
The above described coplanar line filter or duplexer may further comprise input/output terminal portions provided on said dielectric substrate, said input/output terminal portions comprising a second center conductor and a ground conductor provided with a gap therebetween, and the second center conductors of said input/output terminal portions being electrically connected to the first center conductors of said &lgr;/4 coplanar resonators.
By the above described structure and arrangement, the input/output terminal portion is provided on the same flat surface of the dielectric substrate as the coplanar resonators. With this arrangement, coupling of the coplanar line filter via this input/output terminal portion to an external circuit is stronger than a coupling of a coplanar line filter to an external circuit via a conventional capacitor component. This is also the same in the case of a duplexer.
Furthermore, in the above described coplanar line filter or duplexer, the first center conductors of the &lgr;/4 coplanar resonators may be provided in a zigzag shape to thereby reduce the length of the coplanar line filter or duplexer. In addition, since the distance between the &lgr;/4 coplanar resonators is reduced, it is possible to connect the resonators in series and electromagnetically join them to form a bias circuit.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.
REFERENCES:
patent: 4233579 (1980-11-01), Carlson et al.
patent: 4614925 (1986-09-01), Kane
patent: 5004992 (1991-04-01), Grieco et al.
patent: 5105173 (1992-04-01), Itou
patent: 5376908 (1994-12-01), Kawaguchi et al.
patent: 5612656 (1997-03-01), Sakamoto et al.
Murata Manufacturing Co. Ltd.
Nguyen Patricia T.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
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