A wideband balanced bandpass filter with common-mode suppression using defected ground structure

A microstrip wideband balanced bandpass filter (BPF) with defected ground structure is presented. Firstly, a four-port microstrip differential-mode BPF is designed. Then, the defected ground structure is employed to suppress the common-mode responses while it has very little impact on the differential-mode responses. Finally, the balanced BPF is designed and optimized. Simulated and measured results show good performances of the proposed balanced BPF, such as differential passband with sharp roll-off and wide stopband performance, and common-mode suppressing.