Detection of a polarization imbalance in reverberation chambers and how to remove it by polarization stirring when measuring antenna efficiencies

It has previously been shown that the radiation efficiency of small antennas can be measured with good accuracy in reverberation chambers. The results are obtained by averaging several measurements of the transmitted power between the antenna under test and a fixed antenna, both located inside the chamber. Further investigations have shown that the results depend strongly on the orientation of the antenna under test and thereby on its polarization. The present Letter explains why it is like this, and how this imbalance can be removed by polarization stirring, that is, by using three orthogonal fixed antennas instead of one. (C) 2002 Wiley Periodicals, Inc.