On determining the directivity of electrically large, unintentional electromagnetic radiators — Assessment of a real electronic equipment

Several CISPR and IEC standards describe different procedures for the measurement of the radiated disturbance of electronic equipment. The limits are only defined for testing on an open area test site (OATS) so that the results obtained in an alternative test site need to be correlated with those values. An important measure for this post-processing is the EUT's directivity. However, for electrically large, unintentional radiators, the maximum directivity is not known by design; especially for frequencies above 1 GHz. Hence, stochastic approximations which estimate the directivity of arbitrary EUTs have been developed in the past. Yet, this approach is only validated for generic EUTs but not for “real” electronic equipment. This paper addresses the topic and exemplarily assesses the directivity of a computer mainboard. Due to the signal characteristics of a “real” EUT, a discussion about the measurement receiver arises and opens a second topic which is addressed in this paper.