Impedance analysis of EMI filter circuitry used for estimation of the spurious components and boundings

One of the problems in the design of powerline EMI filters is the uncertainty and ambiguity of their source/load impedances which results in breach of expected filter parameters in a real installation. To cover the uncertainty of these terminating impedances, the producers of the filters usually give for their EMI filters the measured insertion loss in several different impedance conditions. This measurements are usually done in harmony with the international standard CISPR 17. These measurements cover frequency range up to 30 MHz and they are also time consuming. In past the author provide several approaches to come up with the method for creation the EMI filter model directly from measured data in the 50 Ω/50 Ω. This approach is complicated by the ignorance of the real spurious components of the EMI filter. So for this reason, this article is focused on the identification of this spurious components of the EMI filters. Each branch of the filter is measured separately by the VNA and after that the performance is compared with the data taken from the simulations. The resonance frequencies are nicely significant in measured data and in calculated as well.