On the Number of Independent Samples Available in a VIRC Over a Long Exposition Time and the Potential Detection of Periodical Stirring Patterns

A procedure able to compute the number $N_{\text{ind}}$ of independent samples obtained during a long time sequence (typically lasting several tens of seconds) in a vibrating intrinsic reverberation chamber (VIRC) (which is a reverberation chamber made with a flexible metallized textile) is presented. The procedure which requires to measure time-domain $S$-parameter measurements at each frequency of interest is proved to be independent of the antenna positions within the VIRC. This approach using updated correlation assessment methods clearly highlights the importance of the stirring process randomness implemented to move the canvas. The detection of repetitive (or periodical) patterns of the stirring process is shown to be of prime importance as this situation would lead to a drastic decrease of $N_{\text{ind}}$. If the stirring process is excellent (and without any repetitive pattern), the number of independent samples able to be collected at a given position in a VIRC is shown for the first time to be proportional to the exposition (or acquisition) time. This makes a VIRC a good candidate for reverberation chamber applications requiring a low uncertainty budget, and this without the need to move any object inside the chamber during these measurements unlike in classical parallelepipedal reverberation chambers. This also simplifies both the experimental setup as well as the definition of the stirring sequence which requires only to collect measurements with a time interval larger than the “uncorrelation time” which is known to be lower than a second in a VIRC.