An UWB high-q bandpass filter with wide rejection band using defected ground structures

In this paper, an ultra-wideband microstrip bandpass filter (BPF) which operates from 2 GHz to 4.7 GHz, with high selectivity and wide rejection band is presented and experimentally verified. The filter is composed of microstrip lines with shorted stubs acting as a high pass filter (HPF) on top side and dumbbell shaped defected ground structures (DGSs) on bottom side acting as a low pass filter (LPF). The seventh order high pass filter structures and three dumbbell shaped DGS resonators combined on a single layer microstrip substrate are optimized using microwave circuit and electromagnetic (EM) simulation tools to obtain the ultra-wideband bandpass filter. The designed compact filter has 0.9 dB max insertion loss in-band, no harmonics are observed up to and above 12 GHz and finally, it has a good selectivity. The designed hybrid circuit is a production friendly and low cost bandpass filter which has a controllable pass- and rejection band nature.