Design of lowpass filter with ultra-wide stopband and high selectivity based on DGS resonators

A new defected ground structure with two transmission zeros is presented. This structure is composed of a dumbbell defected ground structure and a pair of coupling stubs. In contrast to a single finite attenuation pole characteristic offered by the conventional dumbbell DGS, the proposed DGS cell provides dual finite attenuation poles that can be independently tuned. By controlling the position of the two attenuation poles, High selectivity and ultra-wider stopband could be realized simultaneously. A lowpass filter with a cut off frequency of 3.2 GHz and ultra-wide stopband up to 30 GHz utilizing four cascaded DGS cells proposed is designed, fabricated and measured. The results obtained from simulation and measurement have good agreement.