A Tunable Cross-coupled Trisection Bandpass Filter with Constant Bandwidth Based on Dual-mode Resonators

Sheng Wang, Qianyin Xiang* and Quanyuan Feng

School of Information Science and Technology, Southwest Jiaotong University, Chengdu, China, 611756;

ABSTRACT: A novel third-order tunable cross-coupled trisection bandpass filter (BPF) based on dual-mode resonators is presented in this letter. Electric and magnetic dominant coupling path can be constructed by using two coupled dual-mode resonators (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 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 1.64GHz to 2.16GHz, maintaining a -3dB bandwidth of 119.5±3.5 MHz, and a Tz is generated at the lower side of the passband.