Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type
Reexamination Certificate
2001-03-26
2004-05-04
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Nonreciprocal gyromagnetic type
C333S024200
Reexamination Certificate
active
06731183
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a non-reciprocal circuit device such as a circulator, an isolator, etc., particularly to a miniaturized, low-loss, highly reliable non-reciprocal circuit device and wireless communications equipment such as a cellular phone comprising such a non-reciprocal circuit device.
BACKGROUND OF THE INVENTION
Non-reciprocal circuit devices such as circulators, isolators, etc. have characteristics of transmitting a signal to only a particular direction while preventing the signal from being transmitted in the opposite direction, and thus are indispensable parts for transmission circuits of microwave transmission equipment for automobile phones, etc. In such applications, the non-reciprocal circuit devices are required to be miniaturized and reduced in loss. A non-reciprocal circuit device, for instance, an isolator, comprises a magnetic body such as a garnet member, etc., three central conductors disposed on the magnetic body such as a garnet member while overlapping at a 120° interval with electric insulation from each other, a permanent magnet for applying a DC magnetic field to the magnetic body, matching capacitors and a metal case serving as a magnetic yoke and containing these parts.
FIG. 15
shows an isolator, one example of the conventional non-reciprocal circuit devices, disclosed in Japanese Patent Laid-Open No. 11-205011. This isolator comprises a box-shaped resin-conductor composite base
96
disposed on a lower case
92
, the resin-conductor composite base
96
having recesses
100
for respectively receiving a central conductor assembly
4
comprising three central conductors
11
a
-
11
c
disposed on a garnet member
12
with electric insulation from each other, matching capacitors constituted by three flat capacitors
94
a
-
94
c
, and a chip resistor
95
. Each recess
100
of the resin-conductor composite base
96
is defined by an insulating thermoplastic resin partition
101
for positioning each part. Formed at the bottom of the recess
100
is a ground electrode
102
(indicated by hatching) for connecting the central conductor assembly
4
and the capacitors
94
a
-
94
c
to a ground. Each central conductor
11
a
-
11
c
has one end connected to an electrode of each capacitor
94
a
-
94
c
and the other end connected to a ground electrode
102
on the resin-conductor composite base
96
. Each flat capacitor
94
a
-
94
c
has two opposing electrodes, one connected to each central conductor
11
a
-
11
c
, and the other connected to the ground conductor
102
. A resistor
95
is connected to the flat capacitor
94
c
in parallel. A permanent magnet
93
for applying a DC magnetic field to the central conductor assembly
4
is disposed in an upper case
91
, which is combined with the lower case
92
to constitute an isolator.
Each of the upper case
91
and the lower case
92
is formed by an iron-based magnetic sheet such as SPCC (cold-rolled steel sheet) plated with silver for functioning as a magnetic yoke constituting a magnetic circuit for applying a magnetic force of the permanent magnet
93
to the central conductor assembly
4
. A conductor plate constituting the ground electrode
102
in the resin-conductor composite base
96
is bent to integrally have ground terminals
97
b
,
97
c
exposing from the lower and side surfaces of the resin-conductor composite base, exposed portions of the conductor plate being plated with silver. The resin-conductor composite base
96
is provided on a lower surface with an input/output terminal
97
a
and ground terminals
97
b
,
97
c
. Though not shown, the opposite surface of the resin-conductor composite base is also provided with an input/output terminal
97
a
and ground terminals
97
b
,
97
c
. Accordingly, each of the two central conductors
11
a
,
11
b
has one end connected to the input/output terminal
97
a
via the flat capacitor
94
a
,
94
b
, and the other end connected to the ground terminal
97
b
,
97
c
via the ground electrode
102
. The remaining one central conductor
11
c
is connected to the ground terminal
102
for termination via the capacitor
94
c
and the resistor
95
.
FIG. 16
shows an isolator, another example of the conventional non-reciprocal circuit devices, disclosed in Japanese Patent Laid-Open No. 9-55607. This isolator has matching capacitors formed inside a laminate module
105
disposed on a lower case
92
, and the laminate module
105
having a center opening
110
for receiving a garnet member
12
and a central conductor assembly
4
constituted by three central conductors
11
a
-
11
c
, one end of each of three central conductors
11
a
-
11
c
being connected to a capacitor
106
a
-
106
c
printed on an upper surface of the laminate module
105
. A capacitor
106
c
connected to one central conductor
11
c
is electrically connected to a resistor
107
in parallel. The other ends of three central conductors
11
a
-
11
c
are directly connected to the lower case
92
without using a ground plate. A permanent magnet
93
for applying a DC magnetic field to the central conductor assembly
4
is disposed in the upper case
91
, which is assembled to the lower case
92
to constitute an isolator.
Formed in the laminate module
105
are three matching capacitors in single or multi-layers, and electrodes of the matching capacitors are connected to each other through via-electrodes in the laminate module
105
, or external terminals of an input/output terminal
108
a
and ground terminals
108
b
,
108
c
printed on side surfaces of the laminate module
105
as in this example. The laminate module
105
has projections
112
on both sides of a lower surface thereof, onto which an input/output terminal and ground terminals (not shown) are mounted, and a recess
114
between the two projections
112
is formed with an electrode (not shown) for connecting to the lower case, whereby the ground terminals are connected to the lower case-connecting electrodes. The other ends of the central conductors
11
a
-
11
c
, namely the side of the central conductors
11
a
-
11
c
connected to the lower case
92
, are connected to a ground in a circuit board via the lower case
92
and the lower case-connecting electrode and the ground terminals
108
b
,
108
c
of the laminate module
105
.
The market of microwave communications equipments such as cellular phones, etc. has dramatically been expanding recently, accompanied by the rapid miniaturization of cellular phones. Arising with the miniaturization of cellular phones is a strong demand to miniaturization of such parts as isolators, etc., and particularly the isolators are most strongly demanded to be small in size and low in loss. If the conventional isolator disclosed in Japanese Patent Laid-Open No. 11-205011 were to be miniaturized, then parts such as a garnet member
12
, flat capacitors
94
a
-
94
c
, etc. would have to be miniaturized. The capacitance of a capacitor is expressed by
C=&egr;
r
·&egr;
o
·S/d
(1)
wherein C is a capacitance of a capacitor, &egr;
r
is a specific dielectric constant of a dielectric body, &egr;
o
is a dielectric constant of vacuum, S is an area of an electrode, and d is a thickness of a dielectric body between the electrodes.
The formula (1) indicates that to keep the same level of capacitance even when the electrode area S is reduced by the miniaturization of the matching capacitor, it is necessary to use a dielectric body with a large specific dielectric constant &egr;
r
or to reduce the thickness d of a dielectric body between the electrodes. However, dielectric bodies having large specific dielectric constants generally tend to have large dielectric loss, resulting in the loss characteristics of capacitors and thus increase in the loss of isolators.
When a dielectric body disposed between the electrodes has a small thickness, its handling is difficult during the production process, resulting in cracking and breakage of capacitors, leading to a poor yield. When a garnet member has a small diameter, a central conductor assembly comprisi
Horiguchi Hideto
Ichikawa Koji
Itoh Hiroyuki
Sugiyama Yuta
Watanabe Shuichi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Hitachi Metals Ltd.
Jones Stephen E.
Pascal Robert
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