Low-loss and high-selectivity bandpass filter with harmonic suppression and piezoelectric transducer tuning

A low-loss and high-selectivity bandpass filter with harmonic suppression and piezoelectric transducer (PET) tuning is presented. At the 3.5 GHz passband, the insertion loss is 1.48 dB, and the transmission zeros at 3.05 and 4.08 GHz have rejection of 55 dB. The rejection at the 7 GHz second harmonic is 50 dB. A PET tunes the bandstop sections to obtain a tunable suppression (>45 dB) around the second harmonic from 5.35 to 7.8 GHz.