A compact ultra-wideband bandpass filter design based on open stub loaded SIR structure

Based on stepped impedance resonator (SIR) and open stub loaded resonator structure, An ultra-wideband (UWB) bandpass filter is presented in this paper. A interdigital coupledline with four open stubs at the end has been used to control parasitic passband, which can ensure the frequencies of parasitic passband be away from the frequencies of ultra-wideband frequency. An X-slot is created to improve the UWB BPF's passband performance. The filter is simulated by 3D EM commercial software HFSS, The resulting indicates that the presented UWB BPF covers the frequency range from 3.1-10.6 GHz, The return loss is greater than 15 dB and the insertion loss is below 0.6 dB in most part of the passband.