Dual-Mode Cavity Filter With Reconfigurable Bandwidth and Frequency

A frequency-and bandwidth-tunable filter based on dual-mode movable microstrip-cavity structure is proposed in this letter. The TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> and TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> modes of the cavity are employed as the resonant modes. To realize frequency and absolute bandwidth (ABW) tunings, a microstrip feeding line with a movable metal ground is introduced. By moving the metal ground, the external couplings of the two modes are controlled simultaneously. Dielectric posts are inserted into the cavity to independently change the frequencies of the two modes. In this approach, a dual-mode filter with reconfigurable frequency and ABW is obtained using single-cavity resonator. From the measurement, over the frequency tuning range from 8.5 to 10 GHz, variable ABWs are achieved and the insertion loss is kept below 1 dB in the tuning procedure. Hence, the proposed design possesses high-performance filtering response and wide tuning ranges, making it competitive in the multiband radio frequency (RF) front end.