Bandwidth enhancement of ultra-wideband microstrip bandpass filter using defected ground structure

In this paper, the bandwidth enhancement of ultra-wideband (UWB) microstrip bandpass filter (BPF) is proposed by utilizing defected ground structure (DGS). The initial UWB microstrip BPF which is designed to have the bandwidth response of 4 GHz with the center frequency of 4 GHz is deployed on FR4 Epoxy dielectric substrate with overall size and thickness of 11 mm × 32 mm and 0.8 mm respectively. To enhance the bandwidth response, an attempt is carried out by applying DGS on to the ground plane of initial filter. Here, the proposed DGS is constructed of 3 circular dumbbells. Some parametrical studies to the DGS such as changing the radius of dumbbells and the dimension of bridging-section of dumbbells are conducted intensively to obtain the optimum geometry of DGS with the desired bandwidth response. From the characterization result, it shows that the utilization of DGS on to the ground plane of filter has widened 3 dB bandwidth response up to 5.36 GHz ranges from 1.84 GHz to 7.2 GHz yielding an enhanced ultra-wideband response for various UWB applications. The minimum insertion loss and maximum return loss of microstrip BPF with proposed DGS in the passband area are 2.05 dB and 6.73 dB, respectively.