Tunable Bandpass Filter With Continuously-Tuned Center Frequency And Bandwidth

Abstract

This paper presents a bandpass filter with electricallytunable center frequency and bandwidth. The proposed filter employs a centrally-loaded resonator with three varactors. The odd-mode and even-mode resonant frequencies of the resonator can be flexibly controlled by changing the voltage of the corresponding varactors. The adjustability of center frequency is achieved by adjusting both odd- and even-mode resonant frequencies, and the tuning of bandwidth can be achieved by probably adjusting the discrepancy between odd- and evenmode resonant frequencies. To improve the selectivity, the source-load coupling is utilized to generate transmission zeros. The performance of this electronically tuned filter is promising in terms of continuous center frequency and bandwidth tunings. For validation, both theory and experimental results are provided. It is shown that the filter could operate within the frequency range from 525MHz to 655MHz and be applicable to cognitive radio systems.