  Reverberation chambers are currently used to test electromagnetic
compatibility as well as to characterize antenna efficiency, wireless devices,
and MIMO systems. The related measurements are based on statistical averages
and their fluctuations. We introduce a very efficient mode stirring process
based on electronically reconfigurable metasurfaces (ERMs). By locally changing
the field boundary conditions, the ERMs allow to generate a humongous number of
uncorrelated field realizations even within small reverberation chambers. We
fully experimentally characterize this stirring process by determining these
uncorrelated realizations via the autocorrelation function of the
transmissions. The IEC-standard uniformity criterion parameter $\sigma_{dB}$ is
also investigated and reveals the performance of this stirring. The effect of
short paths on the two presented quantities is identified. We compare the
experimental results on the uniformity criterion parameter with a corresponding
model based on random matrix theory and find a good agreement, where the only
parameter, the modal overlap, is extracted by the quality factor.
