LOWPASS FILTER WITH WIDE STOPBAND AND SHARP SKIRT USING NOVEL DEFECTED GROUND STRUCTURE

A novel defected ground structure unit is presented in this paper. This structure is composed of a traditional dumbbell DGS and a pair of coupling stubs in the aperture. In contrast to a single finite attenuation pole characteristic offered by the conventional dumbbell DGS, the proposed DGS unit provides dual finite attenuation poles that can be independently controlled. By adjusting the position of the two attenuation poles, a much sharper skirt and wider stopband could be achieved. A lowpass filter with a cut off frequency of 3.2 GHz utilizing four cascaded novel DGS units is designed, fabricated and measured. This lowpass filter achieves a wide stopband with over 30dB attenuation up to 30 GHz. The results obtained from simulation and measurement have good agreement.