Abstract: A tri-band bandpass filter has been designed using open-loop resonator with open and short stubs. The filter can control each center frequency independently. An odd-even mode analysis is performed on the resonator. The center frequencies of the first and third passbands are obtained with the even mode, and determined by the electrical length and impedance ratio of the stubs. The center frequency of the second passband is obtained with the odd mode and determined by the electrical length and impedance of the open-loop. The filter has triple passband center frequencies of 1.57 GHz for GPS, 2.4 GHz for WLAN, and 3.5GHz for WIMAX, with 3dB fractional bandwidths of 2.5%, 4.7%, and 2.0% , respectively. Measurement results are in general agreement with EM simulation results.

Key words: open-loop resonator, tri-band;bandpass filter (BPF);odd-even mode;open andshort stubs loaded