Directivity of equipment and its effect on testing in mode-stirred and anechoic chamber

If radiated susceptibility testing in a mode-stirred chamber (MSC) is used to test equipment that in its real operation may become irradiated by plane waves it is necessary to increase the test level, i.e. add a margin. In order to find out typical magnitudes of this margin coupling measurements to the interior of several objects have been carried out both in mode-stirred and anechoic chamber (AC). The results show that the maximum coupling in the anechoic chamber is 10-15 dB higher than the coupling measured in the mode-stirred chamber. Also, the assumption of isotropic field conditions in the mode-stirred chamber is strongly supported by the measurements. Finally, it is shown that the statistical distribution of the equipment´s internal field when rotating the stirrer in an MSC is not the same as when the angle of incidence is varied in an AC