Determining the lowest usable frequency of a frequency-stirred reverberation chamber using modal density

This paper aims to determine the lowest usable frequency (LUF) of an unloaded frequency-stirred reverberation chamber with a theoretical approach based upon modal density. Taking into account the composite Q factor, the number of excitable modes is computed as a function of the central frequency of each stirring bandwidth. In a recent work, a relationship was established between the relative error on the standardized variance of the electric energy density in a reverberation chamber and the number of significantly contributing modes. In order to achieve the overmoded condition, we propose to compute an acceptable threshold of the relative error on the standardized variance by the Anderson Darling (AD) goodness-of-fit (GoF) test. A geometric approach based on the plane wave spectrum in k-space is used here to correlate the statistical tests. The LUF determined by this approach is very close to the measured LUF for a 0.423 m × 0.412 m × 0.383 m reverberation chamber built up at the Institute of Electronics and Telecommunications of Rennes (IETR).