A compact common-mode suppression filter for differential signal transmission with slow-wave structure

A compact wideband filter is designed for common mode noise (CMN) suppression in high-speed differential signaling. It is realized by the patch-bridge (PB) patterns on the ground plane beneath the center of differential lines. A two-stage version of the filter units is used to enhance the common-mode rejection level of stopband. Furthermore, a slow-wave structure is introduced between the two filter units, which not only contributes to the miniaturization, but also improves the performance of the proposed CMN filter. The simulated and measured results of the prototype indicate that the CMN can be suppressed over 20 dB from 3.24 to 11.29 GHz by the filter, while good transmission characteristic can be achieved for the differential signals.