Design of a compact UWB bandpass filter with notched band

In this paper, a compact ultra-wideband (UWB) bandpass filter (BPF) with a controllable notched band is proposed and implemented for the application in UWB wireless communication system. Stepped-impedance stub loaded resonator (SISLR), which can generate three resonant modes over the UWB passband with two transmission zeros at both lower and upper stopband, is developed in the filter design with aperture-backed interdigital coupled-lines to improve in-band performance and skirt selectivity. To eliminate the interference of the coexisting wireless local area network (WLAN) within the UWB spectrum, two pairs of folded stepped-impedance resonators (SIRs) are added to the coupled-lines at both sides. The notched band can be easily generated, the bandwidth of which are controllable by adjusting the gaps between the folded SIRs and the coupled-lines. The design is successfully realized and verified by the simulations and experiments.