The Study of Electromagnetic Interference Measurement Technique Based on Wavelet Analysis
基于小波分析的电磁干扰测量技术研究

A innovative digital signal processing technique for fast measurements of ElectroMagnetic Interference(EMI) from devices under test in the time-domain at open area test sites is presented. Suppressing ambient noise by using the wavelet analysis, the EMI measurements of an Equipment Under Test(EUT) can be performed at a test site polluted with electromagnetic ambient noise. Frequency-domain threshold funtion filtering using the wavelet analysis method is applied. The coherence of ambient noise is computed by using the wavelet analysis in time domain and frequency domain. With the characteristic of ambient noise, it can be suppressed by the threshold function in the wavelet domain, and the pure electromagnetic radiation can be obtained readily. The EMI measurement can be performed without the anechoic chamber. It is seen that it is convenient to perform the EMI measurements while the total cost can be reduced greatly. Measurement results show that the successful cancelation of ambient noise can be obtained in the frequency range of 30 Hz to 1000 MHz.