Miniaturized Common-Mode Filter Using Coupled Synthesized Lines and Mushroom Resonators for High-Speed Differential Signals

A miniaturized common-mode (CM) filter, implemented by coupled synthesized microstrip lines and modified mushroom resonators, is proposed and validated on a three-layer printed circuit board. Four identical unit cells with synthesis equations are developed and cascaded. According to the experiments, this miniaturized filter provides a good compromise between circuit size and electrical performance; it is the second smallest design ever reported but with better CM suppression and wider differential-mode operating bandwidth.