A multi-parameter tunable filter based on different U-type resonators

A multi-parameter tunable filter based on different U-type resonators was proposed in this letter. Through the introducing of back-to-back U-type resonator between two typical U-type resonators, the source/load cross coupling can be introduced between the input/output ports to improve the out of band suppression performance of the filter. Adopting of the structure, the center frequency and the cutoff frequency at the high-frequency end of the bandpass filter can be tuned and the one at low-frequency remains unchanged at the same time. A tunable filter with three resonators was designed, fabricated and measured. The simulated results were agreement well with the measured ones.