Ultra-wideband multi-stub loaded ring resonator bandpass filter with a notched-band

In this paper, a novel compact ultra-wideband (UWB) microstrip bandpass filter (BPF) with a notched band using the proposed multi-stub loaded ring resonator (MSLRR) is presented. The MSLRR is constructed by loading four open stubs in a ring resonator, i.e., one pair of high-impedance stub at the top side and another two low-impedance stubs at the bottom side locations. Five modes, including two odd modes and three even modes, could be designed within UWB band. Moreover, two transmission zeros (TZs) are generated by the ring structure, leading to a quasi-elliptic function response that enhances the selectivity significantly. Two slotline splitring resonators (SRR) are used to create a narrow notched band at 8.6 GHz. The simulated and measured results are in good agreement and show good in-band filtering performance and sharp selectivity.