Compact UWB bandpass filter with triple notched bands using parallel U-shaped defected microstrip structure

A novel compact ultra-wideband (UWB) bandpass filter (BPF) with triple sharply notched bands and good selectivity is proposed using a parallel U-shaped defected microstrip structure (UDMS). The initial UWB BPF comprises interdigital coupled lines and an E-shaped multiple-mode resonator to achieve two transmission zeros on both sides of the passband, thus improving skirt selectivity. Then, three parallel UDMSs are introduced, which have the properties of achieving the triple band-notched characteristics and providing a high degree of adjusting freedom. To validate the design theory, a microstrip UWB BPF with three notched bands centred at 5.2, 5.8 and 8.0 GHz, respectively, is designed and fabricated. Both the simulation and the experimental results are provided which have good agreement.