辐射测试（CISPR 22）不合格的测试基本原理简析

首先，辐射测试在国际电工委员会CISPR组织发布的标准CISPR 22中有规定测试辐射的方法及相关技术要求、限值等。

标准要求的限值
传导限值：
Limits of mains terminal disturbance voltage

Limits  for conducted disturbance at the mains ports of class A ITE
Frequency range	Limits dB(μV)
	Quasi-peak		Average
0,15 to 0,50	79		66
0,50 to 30	73		60
NOTE The lower limit  shall apply at the transition frequency.

Limits for conducted disturbance at the mains  ports of class B ITE
Frequency  range	Limits dB(μV)
	Quasi-peak		Average
0,15 to 0,50	66 to 56		56 to 46
0,50 to 5	56		46
5 to 30	60		50
NOTE 1 The lower limit shall apply at the  transition frequencies. NOTE 2 The limit decreases linearly with the logarithm of the frequency in  the range 0,15 MHz to 0,50 MHz.

辐射限值：Limits below 1 GHz
Limits for radiated disturbance

Limits for radiated disturbance of class A ITE at a measuring  distance of 10 m
Frequency range     MHz		Quasi-peak limits     dB(μV/m)
30 to 230		40
230 to 1 000		47
NOTE 1 The lower limit shall apply at the transition  frequency. NOTE 2 Additional provisions may be required for cases where  interference occurs.

Limits for radiated disturbance of class B ITE at a measuring  distance of 10 m
Frequency range     MHz		Quasi-peak limits     dB(μV/m)
30 to 230		30
230 to 1 000		37
NOTE 1 The lower limit shall apply at the transition  frequency. NOTE 2 Additional provisions may be required for cases where  interference occurs.

Limits above 1 GHz

Limits for radiated disturbance of Class A  ITE     at a measurement distance of 3 m
Frequency  range     GHz		Average limit     dB(μV/m)		Peak limit     dB(μV/m)
1 to 3		56		76
3 to 6		60		80
NOTE The lower limit applies at the transition frequency.

Limits for radiated disturbance of Class B  ITE     at a measurement distance of 3 m
Frequency  range     GHz		Average limit     dB(μV/m)		Peak limit     dB(μV/m)
1 to 3		50		70
3 to 6		54		74
NOTE The lower limit applies at the transition frequency.

标准要求的测试实验室
传导端子电压骚扰测试


空间辐射发射测试


空间辐射抗饶度测试


辐射发射测试实验室EUT产品放置要求


       总结上述可知，产品放在一个屏蔽的暗室里面的转台0.8m高的绝缘桌子上面，此桌子可以360°旋转。另外，在其待测试产品的另外一端3m或者10m处有一个可以上下1m~4m高度自由移动的天线塔，接收对面转台上面的产品正常工作时产生的以电磁波形式通过空间发射的场强，再连接到外部的接收机进行测量，与其限值进行比较，从而判定是否合格。
       由上分析可知，其测试不合格主要是天线塔上的接收电磁波的天线，接收到对面转桌上面的产品产生的干扰。那么这个产品的干扰是怎么发射出去的，从产品放置的转桌的摆放图中，发现有相关电缆形成的发射天线，产品的外壳、甚至内部PCB的trace都有可能在高频的情况下，形成等效发射天线，从而导致测试不合格。