高速铁路EMC线天线在低频段近场耦合的研究

Study of EMC Antennas Near-field Coupling within Low Frequency Range

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 considered as one of main uncertainties of radiated electromagnetic interference tests.If antennas are not calibrated accurately,they will affect the following processes of tests.So far there are some problems about methods of calibrations of antennas,such as near-field coupling and balun effects to tests,etc.And near-field coupling brings large errors especially in the frequency range of 30MHz to 180MHz.For these problems,this paper firstly describes a numerical method which could consider balun effects and near-field coupling.Then different balun effects on wire EMC antennas are analyzed and a numerical analysis to quantify near-field coupling is conducted.At last this paper calculates the coupling factors which are based on a specified balun for four ordinary EMC tests and validates the numerical datum as much as possible.