Frequency-variable type filter, duplexer and transceiver

摘要

The invention provides A frequency-variable type filter (1), comprising: a voltage control terminal (CONT 1); at least one resonator (4, 5, 6); and a reactance device capable of being controlled by a control voltage supplied to the voltage control terminal (CONT 1); and the frequency-variable type filter (1) being served as a first filter utilizing a fundamental resonance mode of the resonator (4, 5, 6) when a first control voltage is supplied to the voltage control terminal (CONT 1); whereas the frequency-variable type filter (1) being served as a second filter utilizing a higher resonance mode of the resonator (4, 5, 6) when a second control voltage is supplied to the voltage control terminal (CONT 1).