Determination of the insertion loss of EMI filters using a black-box model

Usually, the insertion loss (IL) of the EMI filter is characterized under 50Q/50Q input and output impedances even if these impedances are different in the real application. In this paper, two approaches are presented to calculate the insertion loss of the filter taking into account the arbitrary input and output impedances. First, a black-box 50Q/50Q model is obtained from S-parameters and then extended to determine the IL of the EMI filter with different impedances. And second, a direct measurement procedure interconnecting the real impedances obtained with the measurement equipment. Both approaches are compared to the real insertion loss calculated from conducted emissions with and without filter.