  The use of correlation matrices to evaluate the number of uncorrelated
stirrer positions of reverberation chamber has widespread applications in
electromagnetic compatibility. We present a comparative study of recent
techniques based on multivariate correlation functions aimed at relating
space-frequency inhomogeneities/anisotropies to the reduction of uncorrelated
positions. Full wave finite-difference time domain simulations of an actual
reverberation chamber are performed through an in-house parallel code. The
efficiency of this code enables for capturing extensive
inhomogeneous/anisotropic spatial volumes (frequency ranges). The concept of
threshold crossing is revised under the light of random field sampling, which
is important to the performance of arbitrary reverberation chambers.
