Wave transmission lines and networks – Coupling networks – Nonreciprocal gyromagnetic type
Reexamination Certificate
2002-06-14
2004-02-10
Tokar, Michael (Department: 2819)
Wave transmission lines and networks
Coupling networks
Nonreciprocal gyromagnetic type
C333S001100
Reexamination Certificate
active
06690248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nonreciprocal circuit device for use in, for example, a microwave band and also relates to a communication apparatus including such a nonreciprocal circuit device.
2. Description of the Related Art
An exemplary isolator, which is a nonreciprocal circuit device, according to the related art will now be described with reference to
FIGS. 11
,
12
A, and
12
B.
FIG. 11
is an exploded perspective view of an isolator according to the related art,
FIG. 12A
is a sectional plan thereof, and
FIG. 12B
is an equivalent circuit diagram thereof.
Referring to
FIGS. 11
,
12
A, and
12
B, reference numeral
1
indicates a ferrite member,
2
generally indicates center conductors (
2
a
is a center conductor for an input port,
2
b
is a center conductor for an output port, and
2
c
is a center conductor for a terminating port),
3
is a magnetic assembly,
4
is a housing,
5
is an upper yoke,
6
is a permanent magnet,
7
is a spacer,
8
is a lower yoke,
9
is an input terminal,
10
is an output terminal,
11
are ground terminals, R is a resistor, C
1
, C
2
, and C
3
are capacitors, and H indicates the direction of a magnetic field applied to the ferrite member
1
.
The center conductors
2
are defined by the center conductor
2
a
for an input port (input-port center conductor
2
a
), the center conductor
2
b
for an output port (output-port center conductor
2
b
), and the center conductor
2
c
for a terminating port (terminating-port center conductor
2
c
). The center conductors
2
a
to
2
c
are arranged so as to cross one another on the ferrite member
1
. The center conductors
2
a
to
2
c
and the ferrite member
1
define the magnetic assembly
3
.
The housing
4
is provided with the lower yoke
8
, the input terminal
9
, the output terminal
10
, and the plurality of ground terminals
11
. The housing
4
accommodates the magnetic assembly
3
, the permanent magnet
6
for applying a static magnetic field to the magnetic assembly
3
, the spacer
7
separating the magnetic assembly
3
and the permanent magnet
6
, the capacitors C
1
, C
2
, and C
3
, which define matching elements, and the resistor R, which defines a terminating resistor. The upper yoke
5
covers the upper portion of the housing
4
.
In the housing
4
, the capacitor C
3
and the resistor R are connected to one end of the terminating-port center conductor
2
c
. The capacitors C
1
and C
2
are connected to the input-port center conductor
2
a
and the output-port center conductor
2
b
, respectively. The center conductors
2
a
to
2
c
, the capacitors C
1
to C
3
, and the resistor R are connected to the corresponding ground terminals
11
provided in the housing
4
. An input port
109
is arranged such that one end of the input-port center conductor
2
a
is connected to the input terminal
9
and the capacitor C
1
is connected between the one end of the input-port center conductor
2
a
and the corresponding ground terminal
11
. An output port
110
is arranged such that one end of the output-port center conductor
2
b
is connected to the output terminal
10
and the capacitor C
2
is connected between the one end of the output-port center conductor
2
b
and the corresponding ground terminal
11
. In addition, a terminating port
111
is arranged such that the capacitor C
3
and the resistor R are connected in parallel between the terminating-port center conductor
2
c
and the corresponding ground terminals
11
.
In this state, an electromagnetic wave entering from the input terminal
9
is output from the output terminal
10
, while an electromagnetic wave entering from the output terminal
10
is absorbed by the resistor R of the terminating port
111
, and thus, is not output to the input terminal
9
, thereby functioning as an isolator.
However, such a nonreciprocal circuit device of the related art has the following deficiencies.
Typically, in a mobile communication apparatus, and particularly a battery-operated communication apparatus, such as a portable communication apparatus, active elements such as a transistor for a power amplifier, are operated by, for example, a power supply having a low voltage of about 3 V to about 4.5 V. When 1 watt of power is required in such a low voltage operation, the load impedance of the active element is about 3&OHgr; to about 5&OHgr;. On the other hand, an antenna, antenna duplexer, and switch are typically configured to have a characteristic impedance of about 50&OHgr;.
An isolator, which defines a nonreciprocal circuit device, is provided adjacent to the output of the power amplifier, and is used to prevent an increase in power consumption due to stabilizing the operation of the radio wave transmitter or inhibiting load fluctuation, or to prevent the output distortion factor from deteriorating. In this case, since the isolator is configured to have a characteristic impedance of about 50&OHgr;, the power amplifier to be connected to the isolator must include a circuit for converting the 3&OHgr; to 5&OHgr; impedance of the active element of the isolator to the 50&OHgr; impedance of the isolator, such that the return loss does not increase at the input of the isolator. Thus, such a converter circuit has commonly been provided inside or outside a power amplifier. However, the converter circuit experiences problems such as transmission loss, a reduced operating frequency band, and an increased size (required for the space of the converter circuit).
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a compact and low-loss nonreciprocal circuit device that permits direct connection of a low impedance element to the input port without providing an impedance converter circuit, and that permits connection of a low impedance element having a greatly simplified matching circuit as compared to the related art to the input port. Also, other preferred embodiments of the present invention provide a communication apparatus including such a novel nonreciprocal circuit device.
According to a preferred embodiment of the present invention, a nonreciprocal circuit device includes a magnetic assembly in which a center conductor for an input port and center conductors for the other ports are disposed on a ferrite member so as to cross one another. The nonreciprocal circuit device further includes a permanent magnet for applying a static magnetic field to the magnetic assembly, and matching circuits connected to the corresponding center conductors. When the center conductors for the input port and the other ports are viewed as lines, the characteristic impedance of the center conductor for the input port is less than the characteristic impedance of the center conductors for the other ports. This arrangement provides a low-loss wide-band nonreciprocal circuit device having a low input-impedance.
Thus, even when a low-impedance circuit element (e.g., a power amplifier) is connected to a stage prior to the nonreciprocal circuit device, low-loss signal transmission is achieved.
Preferably, the matching circuit connected to the center conductor for the input port includes a series capacitor connected in series to the center conductor for the input port and a parallel capacitor connected between the center conductor for the input port and a ground electrode. This arrangement provides a nonreciprocal circuit device having greatly improved characteristics of impedance matching, input return loss, isolation, and insertion loss over the wider frequency band.
Preferably, the width of the center conductor for the input port is greater than the width of the center conductors for the other ports. This configuration provides a low-loss, wide-band nonreciprocal circuit device having a low input-impedance.
The center conductor for the input are preferably defined by a single conductor element that extends in the width direction thereof, and the center conductors for the other ports are each preferably defined by
Keating & Bennett LLP
Mai Lam T.
Murata Manufacturing Co. Ltd.
Tokar Michael
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