A compact common-mode noise suppression filter for high speed differential signals using defected ground structure

A wideband and compact microstrip filter for common-mode electromagnetic (EM) noise suppression in high speed circuit well beyond GHz is presented in this paper. The noise reduction is realized by using specific etched slots in ground metallic plane as defected ground structure (DGS). The effect of the DGS on the characteristics of the investigated filter is examined. It is proved that the common-mode noise can be reduced by more than 15dB at center frequency of 8.4 GHz with a bandwidth from 5.4 GHz to 11.4 GHz. The differential signal is unaffected. The filter size is comparably small to the wavelength interested and the fractional bandwidth of the stop band is 71%. It is also proved the proposed approach is more efficient and effective for the EM noise reduction after comparison with other conventional filters. The proposed simple method for increasing microstrip line insertion loss for the sake of EM noise suppression can be used extensively in microwave filter design.