A wide stopband microstrip bandpass filter using defected ground structure

Defected ground structure (DGS) has the characteristics of slow wave, wide stopband and compact size. A coupled-line bandpass microstrip filter with the central frequency of 12 GHz is designed by using computer-aided design (CAD) tools, and then, the DGS shape is proposed to optimize the stopband and to restrain the spurious passband. Thus, the stopband of the filter is wider than that of conventional coupled-line filter. The experimental results on a fabricated parallel coupled-line filter using DGS agree with the simulation results very well.