A fully tunable bandpass filter based on convex resonators

A fully tunable bandpass filter based on convex resonators is proposed in this letter. Independent tuning of the center frequency and bandwidth of the filter is achieved by adjusting the tunable capacitors loaded at different positions on the resonator. This tunable filter has the advantages of large design freedom, wide adjustment range, and easy cascading to improve the out of band suppression performance. To verify the proposed idea, a 3-order fully tunable bandpass filter was designed and fabricated. The measured results show that the center frequency of the fully tunable filter can be tuned in the range of 223MHz-537MHz, with a frequency variation range of 82.6%, and a 3dB bandwidth tunable in the range of 54MHz-73MHz.