Use grey system theory to analyze EMI harmonic spectrum

During equipment level electromagnetic interference (EMI) experiment, there always exist some frequency spectrum that excess the emission limit, among which harmonic spectrum is the major component. This paper puts forward a method to specially analyze the EMI harmonic spectrum, using model of grey system theory to construct grey-period model for the EMI harmonic spectrum, and the model turns out to include the total trend component and the harmonic component. This paper also testifies the method in actual test, the result shows that the model accuracy can reach 97%, and it extracts the harmonic component effectively, so that this method can be used to describe the EMI harmonic spectrum and find the harmonic component to make support for the electromagnetic compatibility (EMC) design.