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天线系数是辐射类的电磁骚扰发射(EMI)检测中主要不确定度来源之一,如果天线没有被准确地校准,会影响到后续所有的测试过程。对于天线校准的方法,至今仍然有一些问题尚未很好地解决,譬如未考虑近场耦合问题以及平衡不平衡转换器(balun)对天线系数测量结果的影响等等。尤其是在低频(30M～180MHz)的情况下,近场耦合的影响相当明显,给测量带来很大的误差。针对这些问题,首先描述了一种能计算已知balun结构和近场耦合的数值仿真方法,然后利用该方法分析了不同的balun结构对EMC线天线的影响,并根据特定的balun结构对近场耦合进行了量值分析,最后重点针对常规EMC测试情况,根据特定的balun结构计算出了近场耦合系数,并且在一个实际的测试场地上尽可能地验证了数值计算的结果。
Antenna factor is one of the main sources of uncertainty in the detection of electromagnetic disturbing emissions (EMI) of the radiated species. If the antenna is not accurately calibrated it will affect all subsequent test procedures. As to the method of antenna calibration, there are still some problems that have not been solved so far. For example, the problem of near-field coupling and the influence of the balun on the antenna coefficient measurement are not considered. Especially in the low frequency (30M ~ 180MHz) case, the impact of near-field coupling is quite obvious, to bring great errors to the measurement. In order to solve these problems, a numerical simulation method to calculate the balun structure and near-field coupling is first described. Then the influence of different balun structures on the EMC line antenna is analyzed. Based on the balun structure, Coupling was conducted for the numerical analysis. At last, the near-field coupling coefficient was calculated according to the specific balun structure. Finally, the numerical results were validated as far as possible on an actual test site.