| 摘要 |
PURPOSE:To easily control a filter characteristic, by connecting a negative resistance circuit having an active element to a resonance circuit connected to a transmission line, and increasing/decreasing the Q of the resonance circuit equivalently by energizing/de-energizing the active element. CONSTITUTION:A resonator 31 of lambda/2 is connected to the transmission lines 11 and 12 via a capacitance 21. An amplifier 41 and a phase adjusting line 51 are coupled with capacitances 22 and 23 at the other end of the resonator 31. And by opening/closing a switch 61, an operating power source VB is supplied or stopped to the amplifier 41. By operating the amplifier 41, and cooperating with the phase adjusting line 51, they are actuated as the negative resistance in the neighborhood of a resonance frequency f0, and supply energy to the resonator 31, and remarkably increases the Q of the resonator 31 equivalently. In such way, the filter characteristic can be easily controlled.
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