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.