A Research On EMI Test Using A GTEM Cell

The electromagnetic compatibility of electronic equipment is briefly introduced and the background of the subject is studied in this thesis. Based on electromagnetic interference test, the paper introduces the test sites and test instruments that used in the research, and the special committees for electromagnetic compatibility, as well as standards published by the committees.The three theoretical methods on correlating GTEM cell and OATS emission have been studied based on the electromagnetic field theory and the electromagnetic wave propagation theory. The three methods are Wilson method, Lee method, and a method using antenna factors. For each method, the corresponding formulas have been given, and the measurement processes and guidelines have been confirmed.Software has been designed and developed for EMI test using a GTEM Cell, it is mainly used for calculating the results by using the data that measured in the GTEM cell, and it is a very important tool to study the subject. The software involves many functions, such as, algorithm selecting, model setting, results calculating, results drawing, errors showing, configuration managing and so on. The software has been developed by using single-document application of Visual C++ 6.0, it is user-friendly, easy to operate, and has a great convenience to the observation and analysis.In order to study the performance of the three correlating methods when electronic equipments that with complex radiation characteristics are being tested, the EUT that has a non-uniform field distribution has been made by putting the comb-like signal generator in a metallic box with a small slot. The standard EUT radiation field strength values have been measured in a semi-anechoic chamber that takes replace of the OATS. And the port voltages of the EUT in the GTEM cell have been measured in accordance with the test guidelines. Then, the radiation field strength values of the three methods have been calculated by using the software, and the errors have been gotten by comparison. The possible reasons for the errors have been analyzed. The reasons may be due to test environment, test processes or the theoretical approximation. And the ways to reduce the errors of such reasons have been discussed.Finally, the performances of the three methods have been compared. The results of Wilson method and the method using antenna factors are better. And to Lee method, the vertical electric fields are better than the horizontal electric fields. For ideal situation, such as comb-like signal generators, the results are better than the EUT. That is to say, using a GTEM cell for EMI testing is entirely possible, but further researches and improvements need to be made.