To provide a small sized electronic tuning polar filter that has a steep attenuation pole in the vicinity of a pass band and where the position of the attenuation pole is controlled electronically.
An auxiliary circuit 110 consisting of cascade connection of a variable phase shifter 102 whose phase shift amount is adjustable and a variable attenuator 103 whose attenuation is adjustable is connected to a band pass filter 101 via connection circuits 104, 105 respectively and the phase shift amount and the attenuation are controlled electrically by employing active elements for the variable phase shifter 102 and the variable attenuator 103. An attenuation pole of the title filter is caused at a frequency at which an amplitude of a signal from an input terminal 106 to an output terminal 107 via the band pass filter 101 is the same as an amplitude of a signal from the input terminal 106 to the output terminal 101 via the variable phase shifter 102 and the variable attenuator 103 and a phase of the former signal is opposite to a phase of the latter signal. Since the phase shift amount and the attenuation are controlled electrically, the frequency at which the attenuation pole is produced is easily adjusted. Moreover, circuit integration is possible for the variable phase shifter 102 and the variable attenuator 103 and then they are made small.
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YABUKI HIROYUKI
MAKIMOTO MITSUO
