Wave transmission lines and networks – Coupling networks – Nonreciprocal gyromagnetic type
Reexamination Certificate
2003-08-11
2004-11-09
Jones, Stephen E. (Department: 2817)
Wave transmission lines and networks
Coupling networks
Nonreciprocal gyromagnetic type
C333S001100
Reexamination Certificate
active
06816027
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to three-port nonreciprocal circuit devices, and more particularly, relates to a three-port nonreciprocal circuit device, such as an isolator or circulator, used in a microwave band, and also relates to a communication apparatus including the nonreciprocal circuit device.
2. Description of the Related Art
Typically, isolators operate so as to allow signals to pass only in the transmission direction and to block the transmission in the opposite direction, and are used in transmission circuit sections of mobile communication apparatuses, such as car phones and portable telephones.
Conventionally, as isolators of this type, three-port isolators (isolators having three, i.e., first to third, center electrodes) have been known. As shown in
FIG. 12
, an isolator
100
includes center electrodes
101
,
102
, and
103
, a ferrite element
110
, matching capacitors
105
,
106
, and
107
, and a terminating resistor
108
. A port portion P
1
is connected to one end of the center electrode
101
. An input terminal
114
and the matching capacitor
105
are electrically connected to the port portion P
1
. A port portion P
2
is connected to one end of the center electrode
102
. An output terminal
115
and the matching capacitor
106
are electrically connected to the port portion P
2
. A port portion P
3
is connected to one end of the center electrode
103
. The matching capacitor
107
and the terminating resistor
108
are electrically connected to the port portion P
3
. The matching capacitors
105
,
106
, and
107
and the terminating resistor
108
are connected to corresponding ground.
Meanwhile, in typical communication apparatuses, amplifiers used in the circuits thereof cause signals to be distorted to some extent. This distortion causes spurious components, such as a second harmonic (2 f) and a third harmonic (3 f) of an operating frequency f, to be generated, which is responsible for unwanted emissions. Since unwanted emissions in communication apparatuses causes malfunction and/or interference of power amplifiers, standards and specifications are specified in advance. In order to prevent unwanted emissions, a method in which a filter or the like is provided is commonly used to attenuate unwanted frequency components. The use of such a filter, however, leads to a problem in that loss occurs because of the filter, which is undesirable.
Accordingly, a possible approach for suppressing spurious components is to utilize characteristics of bandpass filters included in the isolators or circulators. However, the nonreciprocal circuit device having the basic conventional configuration shown in
FIG. 12
cannot provide sufficient attenuation characteristics in an unwanted frequency band.
To overcome the problem, Japanese Unexamined Patent Application Publication Nos. 2001-320205 and 2001-320206 disclose nonreciprocal circuit devices that can provide large attenuation in, mainly, a frequency band in which spurious components, such as a second harmonic (2 f) and a third harmonic (3 f) of an operating frequency (f), are generated.
FIG. 13
is an equivalent circuit diagram of an isolator that is one example of the nonreciprocal circuit devices of the related art.
This isolator
120
is different from the isolator
100
shown in
FIG. 12
in that a series inductor
121
is electrically connected between the matching capacitor
106
and ground. Thus, the matching capacitor
106
and the series inductor
121
constitute a trap circuit, which makes it possible to attenuate signals in a frequency band away from the passband.
FIG. 14
is a graph showing the attenuation characteristics of the isolator
100
(Conventional Example 1) shown in FIG.
12
and the isolator
120
(Conventional Example 2) shown in FIG.
13
. Both of the isolators
100
and
120
have a bandpass of 900 MHz. From
FIG. 14
, it can be seen that Conventional Example 2 displays increased attenuations of a second harmonic (2 f) and a third harmonic (3 f) compared to Conventional Example 1.
As discussed in Japanese Unexamined Patent Application Publication No. 2001-320205, one end of each of the three center electrodes
101
,
102
, and
103
in the isolator
120
is electrically connected to a common ground portion having the same shape as the bottom surface of the ferrite element
110
. This common ground portion is brought into contact with the bottom surface of the ferrite element
110
. The three center electrodes
101
,
102
, and
103
extending from the common ground portion are bent so as to be spaced
120
degrees with respect to one another and are arranged on the upper surface of the ferrite element
110
with an insulating sheet interposed therebetween.
However, while the isolator
120
having the trap circuit, which is constituted by the matching circuit
106
and the series inductor
121
, as shown in
FIG. 13
, can increase the attenuations of the second harmonic (2 f) and the third harmonic (3 f) of the operating frequency of a communication apparatus, there are problems in that the insertion loss and return loss characteristics deteriorate and the band width ratio decreases.
FIG. 15
is a graph showing the insertion loss characteristics of the isolator
100
(conventional example 1) shown in FIG.
12
and the isolator
120
(conventional example 2) shown in
FIG. 13
, and
FIG. 16
is a graph showing the output return-loss characteristics thereof. From
FIGS. 15 and 16
, it can be seen that the band width ratio of the isolator
120
decreases.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a three-port nonreciprocal circuit device and a communication apparatus which prevent the propagation of a second harmonic (2 f) and a third harmonic (3 f) of an operating frequency f without deterioration of the insertion loss and return loss characteristics.
A three-port nonreciprocal circuit device according to a preferred embodiment of the present invention includes:
(a) a ferrite element;
(b) a permanent magnet for applying a direct-current magnetic field to the ferrite element;
(c) a first center electrode arranged at a major surface of the ferrite element or in the ferrite element, one end of the first center electrode being electrically connected to a first port;
(d) a second center electrode arranged at the major surface of the ferrite element or in the ferrite element so as to cross the first center electrode in an electrically insulating state, one end of the second center electrode being electrically connected to a second port;
(e) a third center electrode arranged at the major surface of the ferrite element or in the ferrite element so as to cross the first center electrode and the second center electrode in an electrically insulating state, one end of the third center electrode being electrically connected to a third port;
(f) at least one matching capacitor constituting an LC parallel resonator circuit in conjunction with one of the first, second, and third center electrodes, and
(g) at least one series inductor electrically connected between one of the at least one LC parallel resonator and ground.
In addition, the three-port nonreciprocal circuit device is preferably constructed such that the other end of at least one of the first, second, and third center electrodes is not connected to a common potential and does share a common end with another end.
With the arrangement described above, a circuit in which each LC parallel resonator circuit, constituted by the center electrode and the matching capacitor, and the corresponding series inductor are connected provides a trap circuit. This trap circuit can increase the attenuations of the second harmonic (2 f) and the third harmonic (3 f) of the operating frequency f of a communication apparatus without deterioration of the insertion loss and return loss characteristics. The resonant frequency (trap frequency) of the trap circuit, constituted by the LC parallel resonator circuit
Jones Stephen E.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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