A Novel Coplanar Common-Mode Filter With a Wide Stopband

摘要

For the practical design of a common-mode filter (CMF), the substrate uncertainty and process deviations always result in the stopband offset of the CMF at high frequencies. To compensate the stopband offset, in this paper, a general method for expanding the bandwidth of a CMF is proposed. A three-conductor model is used to analyze the coupling characteristic between the CMF and the differential lines, and then etching slot on the ground plane for stopband bandwidth expansion is developed. A wideband CMF with a central frequency around 25 GHz and an all-pass performance (from DC to 40 GHz) for differential signals is designed. Both the simulation and measurement results verify the effectiveness of the proposed improved CMF. The -10 dB stopband bandwidth of the coplanar CMF is increased by five times without SI problems. This greatly increases the robustness of the CMF against the substrate uncertainty and the printed circuit board process deviations.