Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type
Reexamination Certificate
2001-03-02
2003-08-05
Donovan, Lincoln (Department: 2832)
Wave transmission lines and networks
Plural channel systems
Nonreciprocal gyromagnetic type
C333S024200
Reexamination Certificate
active
06603369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to nonreciprocal circuit devices used in a high frequency band such as a microwave band, for example, isolators or circulators. In addition, the invention relates to communication apparatuses incorporating the nonreciprocal circuit devices.
2. Description of the Related Art
In conventional nonreciprocal circuit devices such as lumped-constant isolators and circulators, attenuation in a signal propagation direction is extremely small, whereas attenuation in the opposing direction is extremely large. Conventional nonreciprocal circuit devices having such characteristics are widely used in communication apparatuses to allow oscillators and amplifiers to act in a stable manner and secure functions of the oscillators and amplifiers.
FIG. 8
shows an exploded perspective view of a conventional isolator, and each of
FIGS. 9A and 9B
show the inner structure of the isolator.
FIG. 10
shows an equivalent circuit thereof.
As shown in each of FIG.
8
and
FIGS. 9A and 9B
, in the lumped-constant isolator, inside a magnetic closed circuit formed by an upper yoke
2
and a lower yoke
8
are arranged a magnetic assembly member
5
composed of central conductors
51
,
52
, and
53
, a ferrite member
54
, a permanent magnet
3
, and a 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
and port P
2
of the central conductor
52
is connected to an input/output terminal
72
and a matching capacitor C
2
. The input/output terminals
71
and
72
and the matching capacitors C
1
and C
2
are disposed in the resin frame
7
. 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 the termination resistor R is connected to grounds
73
.
In the equivalent circuit shown in
FIG. 10
, the ferrite member has a disk shape and a direct-current magnetic field is indicated by the symbol H. The central conductors
51
,
52
, and
53
are shown as equivalent inductors L. With such a circuit structure, forward-direction characteristics are equivalent to the characteristics of a band pass filter. In frequency bands distant from the pass bandwidth, 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 always causes distortions to some extent. This is a factor producing spurious components including the second harmonic and the third harmonic of a fundamental wave, by which unnecessary radiation is generated. Since such unnecessary radiation emitted from the communication apparatus causes the malfunction of a power amplifier and interference, standards and regulations for manufacturing the apparatus are pre-determined. Thus, it is necessary to suppress the unnecessary radiation below a certain level. In order to prevent unnecessarily radiation, it is effective to use an amplifier having good linearity. However, since such a amplifier costs much, with the use of a filter or the like, usually, unnecessary frequency components are attenuated. However, still, such a filter costs and the size of the apparatus increases. In addition, there is a loss generated by the filter.
Therefore, it is considerable to suppress spurious components by using 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. 8
to
10
.
In order to solve the above problems and obtain a large amount of attenuation in spurious frequency bands including the second harmonic and third harmonic of a fundamental wave, there is disclosed a nonreciprocal circuit device in Japanese Unexamined Patent Application Publication No. 10-93308. Each of
FIGS. 11
,
12
A and
12
B, and
13
shows an isolator as an example of the nonreciprocal circuit device.
FIG. 11
shows an exploded perspective view of the isolator Each of
FIGS. 12A and 12B
shows the inner structure of the isolator, and
FIG. 13
shows an equivalent circuit of the isolator.
Unlike the isolator shown in each of
FIGS. 8
to
10
, the isolator includes an inductor of for a band pass filter. The inductor Lf is connected between the port P
1
of a central conductor
51
, a matching capacitor C
1
, and an input/output terminal
71
. As the inductor, a solenoid coil adaptable to miniaturization of the device is used. An isolator applied for the 900-MHz band uses a coil having an inductance of approximately 24 nH. More specifically, a coil used in this isolator is formed by a copper wire having a diameter &phgr; of 0.1 mm which is wound 9 turns with an external 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 connection, as in the equivalent circuit shown in
FIG. 13
, the capacitor Cf and the inductor Lf form a band pass filter, with the result that the signal components of frequencies distant from the pass bandwidth can be attenuated.
FIG. 14
shows a graph illustrating frequency characteristics of the isolator (a first conventional example) shown in
FIGS. 8
to
10
and the isolator (a second conventional example) shown in
FIGS. 11
to
13
. This graph shows the frequency characteristics of the isolators applied for the 900-MHz band. When compared with the first conventional isolator, in the second conventional isolator, attenuation or the second harmonic (1800 MHz) is improved from 19.3 dB to 28.3 dB, and attenuation of the third harmonic (2700 MHz) is improved from 28.6 dB to 40.1 dB.
As described above, when the inductor is disposed in the nonreciprocal circuit device to form a filter permitting attenuation of unnecessary frequency components, the entire circuit structure can be made smaller than the structure including a single 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 more compact nonreciprocal circuit device incorporating an inductor for a filter. Thus, it is also necessary to reduce the size of such an inductor. However, when a solenoid inductor is miniaturized, inductance of the inductor becomes smaller, thereby reducing attenuation in the second harmonic and third harmonic of the fundamental wave. In addition, in order to miniaturize such a solenoid inductor without decreasing inductance, it is possibly considerable to provide a solenoid within a magnetic member. However, this arrangement newly requires a magnetic member, and manufacturing of the structure is a difficult task, which increases 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 at a predetermined frequency band without increasing cost. It is another object of the invention to provide a communication apparatus using the nonreciprocal circuit device.
The present invention provides a nonreciprocal circuit device including a magnetic member to which a direct current magnetic field is applied, the magnetic member including a plurality of central conductors arranged to intersect one another, and a series resonant circuit including a capacitor and an inductor. The series resonant circuit is connected between at least one of the central conductors and a ground, and has a resonance frequency greater than the central frequency of a pass bandwidth of the nonreciprocal circuit device. The series resonant circuit is formed by directly connecting a cold end of the capacitor and a hot end or the inductor.
Regarding a communication apparatus, the frequencies of major problematic spurious components generated are higher than a basic wave frequency. Thu
Hasegawa Takashi
Ohira Katsuyuki
Donovan Lincoln
Keating & Bennett LLP
Murata Manufacturing Co, Ltd.
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