Risk to Declare EMC Compliant a Faulty EUT During Radiated Susceptibility Tests Performed in an Undermoded Reverberation Chamber

Abstract

This article investigates the risk to declare compliant a faulty equipment under test during a radiated susceptibility test performed in a reverberation chamber (RC) working imperfectly, i.e., in the lowest frequency range when the chamber is undermoded. The results obtained from an extensive measurement campaign are compared, using the same worst-case approach, to a probabilistic model proposed recently for well-stirred RCs. Below the frequency when the RC can be assumed to be well-stirred, the variance (or the standard deviation) of the electromagnetic field (or of the induced power on the equipment) may strongly differ from the ideal case, depending on the effect of the stirring process and of the modal density. If the variance is low, the test is, as expected, quite meaningless and it makes sense to avoid this corresponding frequency range. However, more surprisingly, if the variance is higher than the one observed in ideal conditions, the risk is paradoxically reduced for weakly susceptible equipment (but increased for highly susceptible ones). Indeed, this higher variance makes the appearance of a strong amplitude of the disturbance for a given stirring configuration more probable. This article is considered as an incremental step in the understanding of the RC behavior from the point of view of radiated susceptibility testing, particularly when the RC is undermoded, a frequency range generally used to perform this kind of tests.