Modification of approximate worst-case measurement system for EMI filters

This paper deals with the approximate worst-case test method for testing the insertion loss of the EMI filters. The systems with 0.1 Ω and 100 Ω impedances are usually used for this testing. These measuring systems are required by the international CISPR 17 standard. The main disadvantage of this system is the 0.1 Ω impedance transformer. The dynamic range for the transformation from the 50 Ω, which is most common matched impedance for the measurement setups, to 0.1 Ω is very large. It is no easy to produce such transformers with this high impedance transformation ratio. These transformers have usually very narrow bandwidth. This paper discusses the alternative system with 1 Ω and 100 Ω impedances. The performance of these systems was tested on several filters and the obtained data are depicted, too. The performance comparison of several filters in several systems is also included. The performance of alternate worst-case system is discussed in the conclusion.