Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type
Reexamination Certificate
2001-03-13
2003-06-17
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Nonreciprocal gyromagnetic type
C333S024200
Reexamination Certificate
active
06580333
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nonreciprocal circuit device such as an isolator or a circulator used in a high frequency band, for example, in a microwave band. In addition, the invention relates to a communication apparatus incorporating the nonreciprocal circuit device.
2. Description of the Related Art
In conventional nonreciprocal circuit devices such as lumped-constant isolators and circulators, attenuation in a signal-propagating direction is extremely small, whereas attenuation in the opposite direction is extremely great. Thus, the conventional nonreciprocal circuit devices having such characteristics are widely used in communication apparatuses to allow oscillators and amplifiers to act in a stable manner while maintaining their functions.
FIG. 19
shows an exploded perspective view of a conventional isolator, and each of
FIGS. 20A and 20B
shows the inner structure of the isolator.
FIG. 21
shows an equivalent circuit diagram of the isolator.
As shown in FIG.
19
and
FIGS. 20A and 20B
, in the lumped-constant isolator, a magnetic assembly
5
composed of a ferrite member
54
and central conductors
51
,
52
, and
53
, a permanent magnet
3
, and a resin frame
7
are arranged in a magnetic closed circuit composed of an upper yoke
2
and a lower yoke
8
. In the resin frame
7
, port P
1
of the central conductor
51
is connected to an input/output terminal
71
and a matching capacitor C
1
. Port P
2
of the central conductor
52
is connected to an input/output terminal
72
and a matching capacitor C
2
. Port P
3
of the central conductor
53
is connected to a matching capacitor C
3
and a termination resistor R. One end of each of the capacitors C
1
, C
2
, and C
3
and one end of the termination resistor R are connected to grounds
73
.
In the equivalent circuit shown in
FIG. 21
, the ferrite member has a disk-like shape and a DC magnetic field is indicated by the symbol H. The central conductors
51
,
52
, and
53
are shown as equivalent inductors L. In such a circuit structure, forward-direction characteristics are equivalent to the characteristics of a band pass filter. In frequency bands distant from the pass band, even in the forward direction, signals are slightly attenuated.
In general, in a conventional communication apparatus, an amplifier used in a circuit of the apparatus usually causes some distortions. This is a factor producing spurious components such as the second and third harmonics of a fundamental frequency, by which unnecessary radiation is generated. Since such unnecessary radiation emitted from the communication apparatus causes the malfunction of a power amplifier and a problem of interference, standards and specifications are determined in advance to suppress the unnecessary radiation below a certain level. In order to prevent the unnecessary radiation, it is effective to use an amplifier having good linearity. However, since such an amplifier costs much, for example, a filter is usually used to attenuate unnecessary frequency components. Still, such a filter is expensive and the size of the apparatus increases. In addition, there is a loss generated by the filter.
Thus, it is considered that spurious components can be suppressed by using the characteristics of a band pass filter included in an isolator or a circulator. However, it is impossible to obtain sufficient attenuation characteristics in unnecessary frequency bands by using the conventional nonreciprocal circuit device having a basic structure shown in each of
FIGS. 19
to
21
.
In order to solve the above problems to obtain a large amount of attenuation in spurious frequency bands such as the second and third harmonics of a fundamental frequency, there is disclosed a nonreciprocal circuit device in Japanese Unexamined Patent Application Publication No. 10-93308. Each of
FIG. 22
,
FIGS. 23A and 23B
, and
FIG. 24
shows an isolator as an example of the nonreciprocal circuit device.
FIG. 22
shows an exploded perspective view of the isolator. Each of
FIGS. 23A and 23B
shows the inner structure of the isolator.
FIG. 24
shows an equivalent circuit diagram of the isolator.
Unlike the isolator shown in each of
FIGS. 19
to
21
, this isolator includes an inductor Lf for a band pass filter. The inductor Lf is connected between port P
1
of a central conductor
51
, a matching capacitor C
1
, and an input/output terminal
71
. As the inductor Lf, a solenoid coil is used, which is adaptable to miniaturization of the circuit structure. An isolator applied in the 1 GHz band uses a coil having an inductance of approximately 24 nH. More specifically, the used coil is formed by making nine turns of a copper wire having a width &phgr; of 0.1 mm with an outside diameter &phgr; of 0.8 mm.
A capacitor Cf is connected in series to the input/output terminal
71
of the isolator having the above structure. With this arrangement, as seen in the equivalent circuit diagram shown in
FIG. 24
, the capacitor Cf and the inductor Lf form a band pass filter. As a result, the signal components of frequencies distant from the pass band can be attenuated.
FIG. 25
shows a graph illustrating frequency characteristics of the isolator (a first conventional example) shown in
FIGS. 19
to
21
and the isolator (a second conventional example) shown in
FIGS. 22
to
24
. This graph shows the frequency characteristics of the isolators applied in the 1-GHz band. When a comparison is made between the first conventional isolator and the second conventional isolator, it is found that attenuation of the second harmonic (2 GHz) is increased from 20.2 dB to 33.3 dB, and attenuation of the third harmonic (3 GHz) is increased from 28.2 dB to 46.4 dB.
Thus, when the solenoid coil is arranged in the nonreciprocal circuit device to form a filter attenuating unnecessary frequency components, the entire circuit structure can be made smaller than the structure including a discrete filter disposed outside of the device.
Recently, with an increasing need for further miniaturization of a mobile communication apparatus, there has been a demand for a smaller nonreciprocal circuit device incorporating an inductor for a filter. Thus, it is also necessary to reduce the size of the inductor for a filter. However, when an inductor formed by a solenoid is miniaturized, inductance of the inductor becomes smaller, thereby reducing attenuation in the second and third harmonics of the fundamental frequency. In addition, in order to miniaturize such a solenoid inductor without causing inductance reduction, it is considerable to form a solenoid inside a magnetic member. However, this arrangement requires a magnetic member and such a structure is difficult to manufacture, increasing cost.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a compact nonreciprocal circuit device in which a large amount of attenuation can be obtained in a predetermined frequency band without increasing cost. It is another object of the invention to provide a communication apparatus using the nonreciprocal circuit device.
According to a first aspect of the invention, there is provided a nonreciprocal circuit device including a magnetic member to which a DC magnetic field is applied, the magnetic member including a plurality of central conductors arranged to mutually intersect, one end of each of the central conductors being grounded, and a plurality of matching capacitors connected to a non-grounded end of each of the central conductors, in which at least one of the matching capacitors has a self-resonance frequency equal to or less than four times the central frequency of a pass band of the nonreciprocal circuit device.
In general, in a nonreciprocal circuit device, parallel resonance circuits are formed by central conductors having inductance components and matching capacitors to obtain matching with the central frequency of a pass band. With this arrangement, attenuation near the central frequency of the pass band can be almost removed. However, in t
Bettendorf Justin P.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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