New compact tri-band bandpass filter with transmission zeros designed by using stub-loaded resonators

Abstract

A new compact tri-band microstrip bandpass filter (BPF) designed based on a tri-mode stub-loaded resonator (SLR) is proposed. The SLR equivalent circuit, consisting of one even mode and two odd resonant modes, can be used to create passbands operated at 2.4, 3.5, and 5.2 GHz, corresponding to the wireless local area networks and WiMAX applications. The filter is compact in size because only two sets of resonator are employed by means of the tri-mode behaviors, and the three band can be designed independently. Furthermore, transmission zero on each passband edges can be created by using 0° feed structures, resulting in high skirt selectivity. Experimental results show good agreement with the simulated ones.