Design of center frequency and bandwidth tunable bandpass filter

This paper presents a center frequency and bandwidth tunable bandpass filter with high selectivity. The proposed filter employs an open stub-loaded resonator with three varactors. The odd-mode and even-mode resonant frequencies of the open stub-loaded resonator can be flexibly controlled, and the tunablities of center frequency and bandwidth can be achieved by probably adjusting both odd-mode and even-mode resonant frequencies. To improve the selectivity and achieve a high out-of-band rejection, the source-load coupling is utilized to generate two transmission zeros on either side of passband. For validation, a demonstration filter is implemented. The performance of this electronically tuned filter is promising in terms of continuous center-frequency and bandwidth tunings.