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.