Design of wideband bandpass filter with high and wide stopband rejection using asymmetrical-loadedstepped-impedance resonator

This study presents a wideband bandpass filter (WBBPF) with wide and high stopband suppression by loading a stepped-impedance resonator (SIR). The prototype of WBBPF is composed of an inverted pi-shaped resonator with T-shaped resonator and open stub loaded, centrally. Odd-/even-mode analysis technique is employed to characterize the resonant properties of this prototype. Then, a SIR is loaded to this filter, asymmetrically, to improve the out-of-band performance. For experimental validation, a WBBPF is designed, fabricated, and tested. The measurement results show that the center frequency of WBBPF is located at 5.095 GHz, and the 3-dB fraction bandwidth is about 71%. Plus, the out-of-band suppression with 30-dB rejection level can be extended to 18.17 GHz.