Novel tunable dual-band filter using evanescent-mode cavity resonators

In this paper, a dual-band filter with highly selective channels and independently tunable channels using evanescent-mode cavity (EVA) is proposed. It consists of four EVA resonators, each of which is topped by a piezoelectric actuator, which is tuned with frequency. Four sets of varactors between two adjacent resonators are used to tune interstage coupling while four sets of varactors are used between ports and resonators for control of the external coupling. By governing resonant frequencies of the EVA resonators and coupling coefficients between adjacent resonators, the independent center frequency tuning ranges of the lower passband and higher passband of the dual-filter are 2.05–2.55 and 2.35–2.75 GHz, respectively. Simulation and measurement results maintain the good agreement.