Evaluation Method for the Probability Distribution of the Quality Factor of Mode-Stirred Reverberation Chambers

An efficient experimental technique is presented for determining the empirical probability distribution of the quality factor ( Q) of a mode-stirred reverberation chamber. The method is based on triplets of S-parameters that are measured at three locations of the receiver and spectrally averaged across a narrow frequency interval. It avoids the need for detailed spatial mechanical scanning of a field sensor. Statistics of the fluctuations of the stored and dissipated energy can be deduced individually. The effective number of excited cavity modes per stir state M at a selected frequency serves as a degrees-of-freedom parameter of the distribution. The value of M is estimated with the method, by fitting the empirical distribution of Q to a Fisher-Snedecor theoretical distribution using nonlinear minimization. Measurement results across 0.1-6.1 GHz support the validity of the theoretical distribution and the experimental technique, indicating that spectral averaging over a band as narrow a few MHz is sufficient within this frequency range to obtain good agreement. For a chosen averaging bandwidth, M is found to increase rapidly with frequency below approximately 1 GHz in our chamber, followed by a slow decrease at higher frequencies. This frequency dependence is interpreted physically.