| 摘要 |
A gain deviation is leveled in the same band by using a varactor diode having the same characteristics as that used in an input tuning circuit for coupling the input tuning circuit and a high frequency amplifier without using a costly and special varactor diode. Means is provided including an input tuning circuit having a tuning varactor diode whose tuning frequency varies with a tuning voltage applied to the cathode of the tuning varactor diode, a high-frequency amplifier provided in a stage subsequent to the input tuning circuit, and a coupling varactor diode for coupling the input tuning circuit to the high-frequency amplifier, in which the cathode of the coupling varactor diode and that of the tuning varactor diode are connected with each other and a bias voltage higher than the voltage at the anode of the tuning varactor diode and lower than the lowest voltage of the tuning voltage is applied to the anode of the coupling varactor diode.
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