Tri-band bandpass filter using modified tri-section and stub-loaded stepped impedance resonators

Abstract

In this letter a compact tri-band bandpass filter (BPF) based on a modified tri-section stepped impedance resonator (SIR) and a stub-loaded SIR is proposed. By properly adjusting the resonant modes of the two resonators independently, a tri-band BPF centred at 1.8/3.5/5.2 GHz is designed, corresponding to the GSM, WiMAX, WLAN applications, respectively. Moreover, several transmission zeros (TZs) are generated on each side of the passbands to improve the selectivity. Measured results show good agreement with the simulated results.