Sharp roll-off lowpass filter using interdigital DGS slot

A novel lowpass filter (LPF) with a sharp roll-off and a wide stopband is presented. The proposed LPF is based on a dual-plane structure with an interdigital shape defected ground structure (DGS). The DGS exhibits a sharp roll-off and three transmission zeros. By tuning the length of the fingers, the resonant frequency can be easily changed. Based on the proposed DGS, a LPF has been designed, fabricated and measured. The transition band is from 3.11 (f_c) to 3.23 GHz with -3.02 and -22.5 dB, respectively. The stopband with rejection better than 25 dB can be extended to 3.4 f_c.