Tri-band bandpass filter using square ring short stub loaded resonators

A tri-band bandpass filter (BPF) using square ring short stub loaded resonators (SRSLR) is presented. The characteristics of the triple-mode resonator are investigated by using even/odd mode analysis. The centre frequencies of the first three passbands can be independently controlled by tuning the dimensions of the SRSLR. Moreover, the filter has been implemented with eight transmission zeros to improve the selectivity. A prototype of a tri-band BPF centred at 2.4, 3.5 and 5.2GHz has been designed and fabricated. Good agreement can be found between the measured and simulated results. © 2012 The Institution of Engineering and Technology.