Design of trisection filter with reconfigurable center frequency and transmission zeros using evanescent-mode cavity resonators

In this paper, a trisection filter with reconfigurable transmission zeros based on the evanescent-mode cavity (EVA) resonators is proposed. The design incorporates three EVA resonators. The varactors are set between two EVA resonators. By controlling the varactor capacitance value, couplings can be switched between electrical coupling and magnetic coupling. Based on this technique, the resulting two zeros can be designed to the desired position. Furthermore, a novel method by analyzing the magnitude and phase of trisection filters is proposed. Using this method, the transmission zeros position can be determined quickly. Measurement shows that the filter covers a frequency range of 2.11–2.83 GHz. Two transmission zeros can be arbitrarily designed to the left or right sides of the passband. Good agreement is obtained between simulated and measured results.