Piezoelectric transducer tunable microstrip bandpass filter with a capacitive coupling

This paper presents a piezoelectric transducer tunable microstrip bandpass filter with a capacitive coupling. A piezo bender transducer together with a alumina substrate tunes the bandwidth and center frequency of a second-order open loop microstrip bandpass filter. A strip alumina substrate is used for the bandwidth tuning and a large-size alumina substrate for the center frequency tuning of the filter. The bandwidth tuning ranges from 102MHz to 152MHz and the center frequency tuning range from 2.37GHz to 2.50GHz with a DC voltage of -50~50V.