Highly Selective UWB Bandpass Filter with Dual Notch Bands Using Stub Loaded Multiple-mode Resonator

In this paper, a low-loss ultra-wideband (UWB) bandpass filter with high selectivity and multiple notch bands is proposed. The filter is based on multi-mode resonator (MMR) which mainly consists of a step impedance transmission line that excites several resonant modes. The MMR structure is loaded a T-shaped open-circuited stub which generate two transmission zeros at the edge of the passband to improve selectivity. Meanwhile, MMR structure is also loaded two pairs of short high impedance stubs to extend the upper stopband of the filter. In addition, to address the in-band interference issues, by coupling a tunable parasitic unit to generate dual band notches at 5.8GHz (WLAN) and 8.1 GHz (X-band). Simulated result indicates that the designed filter’s passband is from 3.18 GHz to 10.67 GHz, the insertion loss is lower than 0.5 dB and its 3 dB relative bandwidth is 108.1%. At the same time, the filter has a high selectivity (30dB skirt factor is 0.917) and a stopband of up to 20 GHz (S
21
< −15dB).