Research Of Field Uniformity Test For Anechoic Chamber

With the development of electronic technology and computer technology, more and more electrical and electronic equipments are used in one system, the networks that connecting equipments become more and more complex. So electromagnetic compatibility problems become more and more important day by day, and at the same time corresponding electromagnetic compatibility testing standards and methods emerged as necessary. In this paper, common test sites for EMC test and the indicators and testing requirements of Anechoic Chamber are introduced firstly, and then the field uniformity test principles of Anechoic Chamber, the testing process of constant power method and constant field method and alternative illumination method for frequencies above 1 GHz are introduced in detail, all of which are according to IEC 61000-4-3 standard.The main task in this paper is to complete two automatic test systems, using the constant power method and constant field method of field calibration for anechoic chamber. VC++ programming language is used in the implementation of the procedures .Both automatic test systems can be divided into three modules, which are the initial information set module, calibration process module (including instrument driver) and data storage, processing and output module. The instrument driver of automatic test system is programmed with the dynamic link library (DLL). Users can only change the instrument driver when using different instruments, which will not affect the main program and can be adapted to different types and manufacturers of instruments. Both automatic test systems can provide users with comprehensive and clear test reports. Users can not only get the basic information of field calibration, but also can get the test result curves in the test report, and the test values at all frequencies can be shown in a table in the test report.Through the on-site test in anechoic chamber of Beijing Jiaotong University, the validity of these two automatic test systems is verified. The similarities and differences between the two testing methods and their advantages and disadvantages are got by comparing the test results of two methods .A more reasonable approach can be chosen to make the test results more accurate and to save more time in the course of the test. Some questions were found when using automatic test system of constant power method and then they were researched in detail. Especially, the test results may be not accurate when the reference field is relatively small, and the solution to the problem is put forward according to the experiment. Finally the calibration of field for frequencies above 1 GHz was researched by using equipment, anechoic chamber, and testing software offered by National Institute of Metrology P.R. China. If a suitable transmitting antenna is adopted, the alternative illumination method according to IEC 61000-4-3 standard can be abandoned, and whether the site is qualified or not can also be judged.