Ultra wideband bandpass filter using microstrip-slot couplers combined with dumbbell slots and H-shaped stubs

A bandpass filter (BPF) that covers the ultra wideband (UWB) frequency range of 3.1 GHz to 10.6 GHz is presented. The filter uses multi-layer microstrip-slot couplers combined with dumbbell slots in the ground plane and H-shaped stubs at the input/output ports to achieve high quality bandpass and band-rejection performance. The simulated results show that the designed filter has a UWB passband with an insertion loss less than 0.5 dB and a return loss greater than 25 dB at the centre of the passband. The device also exhibits sharp and wide low and high frequency stopbands. The simulated group delay of the filter indicates a low peak-to-peak variation of around 0.2 ns across the passband. It features a compact size of 1.5 cm×2 cm when developed on RT6010 with dielectric constant of 10.2.