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为实现对小尺寸箱体电磁屏蔽效能的测试,对嵌套混响室法在频率搅拌方式下的测试原理进行了分析,并从散射参数的定义出发,推导了屏蔽效能的计算方法。根据该方法,在某大型混响室内构建测试系统,利用喇叭天线与制作的单极子天线,对体积为1 m×0.8 m×0.7 m的箱体屏蔽效能进行了测试。测得的S21参数证明了频率搅拌调节场分布的有效性,而S22参数验证了混响室内测得的天线反射系数要高于其实际真值。进一步数据处理表明:屏蔽效能测试结果与天线位置的选取无关,利用改进后的屏蔽效能计算式可有效消除天线类型对测试结果的影响,这将大大提高测试的可重复性。
In order to test the electromagnetic shielding effectiveness of the small box, the test principle of the nested reverberation chamber under the frequency stirring mode is analyzed. And the calculation method of the shielding effectiveness is derived from the definition of the scattering parameters. According to this method, a test system is built in a large reverberation chamber. The horn shielding effectiveness of a 1 m × 0.8 m × 0.7 m box is tested by using a horn antenna and a monopole antenna. The measured S21 parameter proves the validity of the frequency agitation regulation field distribution, while the S22 parameter verifies that the measured antenna reflection coefficient in the reverberation chamber is higher than its actual true value. Further data processing shows that the shielding effectiveness test result has nothing to do with the antenna location selection. The improved shielding effectiveness calculation formula can effectively eliminate the influence of the antenna type on the test result, which will greatly improve the repeatability of the test.