Narrow bandpass filter based on the modified DGS

In this paper, a bandpass filter based on the modified defected ground structure (MDGS) is proposed and its corresponding transmission line (TL) model is developed as well. The resulting bandpass filter provides 1.89 dB insertion loss and 19.2% relative bandwidth. A second order narrow bandpass filter is then investigated by closely coupling two unit cells. This leads to an improvement of 44% in the quality factor. The resulting passband insertion loss is 2.27 dB and the relative bandwidth is 10.7% around 4.2 GHz. Both structures were realized on FR4 substrate, EM simulation, TL model, as well as measurement results are in a very good agreement.