s Planar Microstrip UWB Bandpass Filter with Quad Notched Bands and High Selectivity

Background: This study aims at solving the problems of large design size and insufficient number of the notched band for traditional ultra-wideband (UWB) filters. A planar compact microstrip UWB bandpass filter (BPF) with quad notched bands and good selectivity is proposed using a modified multiple-mode resonator (MMR) and defected ground structure (DGS). Methods: The MMR consists of a stepped impedance stub above and two pairs of open-circuited stubs on both sides, which can generate the passband and double notched bands of UWB filter, the other two notched bands are obtained by DGS. Results: The UWB filter with quad notched bands respectively centered at 3.9 GHz, 5.7 GHz, 7.9 GHz, and 9.8 GHz is fabricated and measured. Conclusion: The measured results are basically consistent with the simulated results, which proves the correctness and practicability of the UWB filter.