A tunable cross‐coupled trisection bandpass filter with constant bandwidth based on dual‐mode resonators

A novel third‐order tunable cross‐coupled trisection bandpass filter (BPF) based on dual‐mode resonators (DMRs) is presented in this letter. Electric and magnetic dominant coupling path can be constructed by using two coupled DMRs to meet the requirement of cross‐coupled tunable bandpass filter with constant bandwidth. Three resonating modes of the two DMRs are used to build the cross‐coupled trisection tunable bandpass filter topology. The coupling structure is analyzed and the coupling coefficients are calculated. The tunable BPF is designed, and a transmission zero (Tz) due to the cross‐coupled trisection topology is generated, so that frequency selectivity is enhanced. The prototype is fabricated and measured. The measured results show that the fabricated circuit realizes a tunable central frequency range from 1.64 to 2.16 GHz, maintaining a −3 dB bandwidth of 119.5 ± 3.5 MHz, and a Tz is generated at the lower side of the passband.