| 摘要 |
PURPOSE:To improve the stability of the device at a frequency except the operating frequency by providing a variable impedance circuit including a capacitor between a main line and a stub so as to improve the microwave characteristic with simple constitution. CONSTITUTION:A high frequency input from a terminal 11 is led to an output terminal 17 via a DC cut-off capacitor 12, a main line 13, an FET amplifier element 14, a main line 15 and a capacitor 16 or the like. The variable impedance circuit including capacitors 21, 22 is formed between the line 13 and the stub 18 and between the line 15 and the stub 19, the impedance of the capacitors 21, 22 is nearly zero at the operating frequency and the open stubs 18, 19 are operated normally to obtain the impedance matching with no loss. On the other hand, the inductive component and resistive component of the capacitors 21, 22 are increased attended with the frequency increase, the impedance matching shows a network including a loss, the reflected power is absorbed and causes to instability and oscillation to the amplifier are suppressed. Thus, the microwave characteristic is improved with simple constitution aud the stability of the device at a freqeuncy other than the operating frequency is improved.
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