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Abstract
A microstrip bandpass filter (BPF) using a novel defected ground structure (DGS) resonators and inter-digital capacitors is proposed in this paper. The BPF is designed by cascading a novel microstrip highpass filter (HPF) and a lowpass filter (LPF). The LPF with a 3 dB cutoff frequency of 6GHz is constructed by a laddershaped transmission line on the top plane and a combined open loop DGS on the bottom one, resulting high selectivity and good stopband performance. The HPF consists of a ladder-shaped transmission line with zigzag slot on the top plane and the open loop DGS on the bottom one, providing two transmission zeros and steep rejection slope. The designed BPF with a 3 dB bandwidth of 2GHz and center frequency of 5GHz exhibits sharp cutoff frequency response. The BPF also shows good stopband performance with rejection better than 20 dB from DC to 3.55GHz in lower stopband and 6.2 to 14GHz in upper stopband, respectively. The measured results agree well with the simulations.