A fully tunable filter based on non-uniform rectangular resonators

A fully tunable filter based on a novel non-uniform rectangular resonators was proposed in this letter. The center frequency and bandwidth can be adjusted independently through the tuning of the varactors loaded at the resonators. At the same time, a cross coupling structure can be easily introduced to improve the selectivity of the filters. In order to verify the effectiveness of the structure described in this letter, a third-order fully tunable filter adopting this structure was designed, simulated, fabricated, and measured. The measured results show that the bandwidth and frequency of the tunable filter can also be tuned. The insertion loss of this filter was better than 1.3dB. The simulated results were in good agreement with the measured ones.