Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
1999-06-02
2001-09-11
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S126000, C455S082000, C455S083000
Reexamination Certificate
active
06288620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna-duplexer and a communication apparatus, used for instance at the microwave band.
2. Description of the Related Art
There is a frequency-variable antenna-duplexer in which an impedance element (switching element), such as a PIN diode or a variable-capacity diode, is connected to a resonator via a capacitor or the like, and the resonant frequency is varied by voltage-controlling these elements. (See for instance Japanese Unexamined Patent Publication No. 7-321509) When a PIN diode is used, the frequency can be switched ON and OFF so that there are two bands, one band during ON and another during OFF. Usually, a positive control voltage is applied to switch the PIN diode ON, and a negative voltage is applied to switch it OFF. A negative voltage is needed for switching OFF because when a high-frequency signal of large electrical power is input, a high-frequency voltage is applied to the PIN diode, thereby switching it ON; a negative voltage avoids this. That is, a negative voltage is needed to prevent the pin diode from becoming unstable when a large power is input, resulting in fluctuating frequency characteristics.
In the above described frequency-variable antenna-duplexer, the impedance element, such as a PIN diode, is nonlinear, and consequently when an unwanted electromagnetic wave enters from the antenna terminal during transmission, the transmission wave F
1
and the intrusive wave F
2
suffer relative modulation. As a result, a spurious signal F
3
(
2
F
1
-F
2
) is generated. Depending on the frequency of the intrusive wave F
2
, the spurious signal F
3
may be the same as the reception frequency. Therefore, in an antenna-duplexer, such relative modulation distortion needs to be reduced as much as possible. This relative modulation distortion occurs when the impedance element has been switched OFF by applying a negative voltage to it.
One method of countering this problem is to increase the negative voltage to stabilize the diode. However, this requires a circuit to generate the large negative voltage, and consequently the communication apparatus cannot be made small-scale. Furthermore, in a third embodiment disclosed in Japanese Unexamined Patent Publication No. 7-321509, two diodes are used for the resonator circuit, instead of generating a large negative voltage. However, since two diodes must be used for all every resonator circuit, there is a problem that an antenna with multiple resonator circuits will be extremely large, making this method inefficient.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention provide an antenna-duplexer and a communication apparatus which have low relative modulation distortion of transmitted waves and intrusive waves, and in addition, are small-scale.
One preferred embodiment of the present invention provides an antenna-duplexer, comprising:
a transmission terminal, a reception terminal and an antenna terminal;
a transmission side circuit, electrically connected between said transmission terminal and said antenna terminal, and comprising at least one first resonator and a first voltage-controllable impedance element which is electrically connected between said first-resonator and ground via either a first inductance or a first capacitor; and
a reception side circuit, electrically connected between said reception terminal and said antenna terminal, and comprising at least one second resonator and a second voltage-controllable impedance element which is electrically connected between said second resonator and ground via either a second inductance or a second capacitor;
a plurality of said first impedance elements being connected in series to said first resonator of said transmission side circuit which is electrically connected closest to said antenna terminal.
Here, PIN diodes, variable-capacitance diodes or field effect transistors are used as the first impedance elements.
With the above constitution, high-frequency voltage can be divided by multiple in-series first impedance elements, connected to the first resonator of the transmission side circuit which is electrically connected closest to the antenna terminal, making it possible to effectively reduce the relative modulation distortion of the transmission waves and intrusive waves, entering from the antenna terminal.
Furthermore, a communication apparatus according to the present invention comprises any one of the antenna-duplexers having the characteristics described above, whereby relative modulation distortion of the transmission waves and intrusive waves from the antenna terminal can be reduced. Thus, the electrical characteristics of the communication apparatus can be improved.
Other features and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention which refers to the accompanying drawings, wherein like reference numerals indicate like elements to avoid duplicative description.
REFERENCES:
patent: 5227748 (1993-07-01), Sroka
patent: 5594394 (1997-01-01), Saski et al.
patent: 6085071 (2000-07-01), Yamada et al.
patent: 7321509 (1995-12-01), None
Atokawa Masayuki
Tsunoda Kikuo
Yamada Yasuo
Glenn Kimberly E
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Pascal Robert
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