Novel lowpass filter with ultra-wide stopband using defected ground structure

In this paper, a novel lowpass filter using defected ground structure (DGS) with a stopband up to 40GHz is realized using Rogers RT5880 substrate ( thickness = 0.508 mm). The filter is combined with two parts, the top single microstrip and the bottom DGS. The simulated and measured results show the great stopband performance of this filter. The passband of this lowpass filter is from 10 MHz to 4.85 GHz, with the typical insertion loss of 0.6 dB and the minimum return loss of 30 dB, while the stopband starts from 5.2 GHz to 40 GHz and all S21 is below −23dB. Compared to other lowpass filter, this filter has an ultra-wide stopband in the same size (80mm * 10mm) and is realized only by DGS rather than modifying the top microstrip.