Compact tri-band bandpass filter designed using stub-loaded stepped-impedance resonator

Abstract

A compact tri-band bandpass filter (BPF) designed using the stub-loaded stepped-impedance resonator (SL-SIR) is presented in this paper. The characteristics of the SIR are firstly studied by using the even-/ odd-mode analysis method. In order to reduce the overall size, a stepped-impedance meander loop resonator is used to design the tri-band BPF. By optimizing the structural parameters, a tri-band BPF operating at 2.45/ 3.5/ 5 GHz is designed and simulated. By adjusting the perturbation size, two degenerate modes are excited and coupling within the first passband. What's more, five transmission zeros which can further improve the performance of the BPF locate on both sides of the three passbands. Simulated results show that the proposed BPF possesses finer frequency response characteristics.