Novel ultra-wide bandpass filter with notched band using multimode resonator and open stubs

In this letter, a novel ultra-wideband bandpass filter with notched band is proposed. This filter is based on multi-mode resonator (MMR) and coupled with the special feed-line structure. The main structure creates the UWB passband from 3.9GHz to 11.1GHz. The notched band was generated around 9GHz by connecting the open-stubs in the original structure. Moreover, the theoretical analysis of the main resonator is given, briefly. The measured results show the feasibility of the filter with the insertion loss lower than 2dB and the average group delay less than 0.4ns. Compared to other UWB filter with notched band, the size of filter is 50% smaller and fabricated in just a single layer of the substrate.