A novel UWB bandpass filter based on quadruple-mode resonator

A quadruple-mode resonator based on stub-loaded was proposed. The resonator possesses four resonances over the wide frequency band from 3.1-10.6 GHz, which can be employed to implement an ultra-wideband bandpass filter(BPF) to achieve flat response. The quadruple-mode resonator is investigated by using odd-even mode analysis and weak coupling method. Two transmission zeroes are located at the upper and lower stopband which improve the selectivity of the UWB BPF. The six transmission poles in passband are created by the quadruple modes resonator and the interdigital coupled feedlines. For verification, a UWB BPF is designed, fabricated and measured. Good agreement is observed between measured and simulated results.