A Skeptic's View of Unstirred Components

In the practice and research on reverberation chambers, the concept of unstirred field components have often been invoked as soon as empirical distributions fail to comply with goodness-of-fit tests applied to data collected at a frequency of operation far beyond the lowest usable frequency. The current explanation for this phenomenon is that under certain conditions, the field samples generated by means of a stirring procedure are not characterized by a zero average-value, but actually present a deterministic offset term that is linked to a line-of-sight contribution. In this paper, we prove that this practice is not sound, as it does not acknowledge the fact that even a very low but non-zero residual correlation between the samples is enough to put in jeopardy the validity of the limits imposed by most hypothesis-test statistics, and hence their ability in properly detecting any constant contribution. An alternative approach is here proposed, based on the analysis of the variability of the line-of-sight contribution estimate, capable of accounting for the residual correlation in a reverberation chamber. Experimental results are presented to support the validity of our approach, exposing the critical use of goodness-of-fit tests as currently applied.