Common and differential mode characterization of EMI power-line filters from S-parameters measurements

A new technique to predict the small signal behavior of EMI power-line filters is presented. This technique is based on S-parameter measurements performed at all the terminals of the power-line filter. These measured S-parameters are converted to a set of modal S-parameters using the presented analytical matrix expressions. The modal S-parameter matrix completely models the small signal behavior of the power-line filter in terms of line and load common and differential modes. From this matrix, information such as common and differential mode insertion loss, modal behavior of the filter at different line and load impedances, and energy transfer between any combination of modes can be obtained.