Abstract:A microstrip bandpass filter using triple-mode ring resonator is presented in this letter. By loading with an open stub, the resonator produces three resonant modes in the pass band. Due to the dual path effect of the ring resonator, two transmission zeros can be introduced at the upper and lower cut-off frequencies, resulting high passband selectivity. Simulation and experimental results show that the center frequency of filter is 5.05GHz, pass band frequency is 4.4-5.7GHz, insertion loss is less than1.7dB in pass band.