On Power Angular Spectrum Estimation in a Reverberation Chamber

The power angular spectrum (PAS) is an important characteristic of the reverberation chamber (RC). Theoretical work suggests that PAS of a well-stirred RC is statistically isotropic, whereas experimental studies show certain degree of anisotropy depending on the RC loading. Since loading is inevitable for both electromagnetic compatibility (EMC) tests and over-the-air (OTA) tests, the PAS is investigated in both frequency and delay domain in this paper. An important finding of this work is that modest loading does not increase the anisotropy in the delay domain. In addition, we show that directive antenna may not be suitable for PAS estimation in the RC and that the periodogram method (for PAS estimation) used in previous literature is equivalent to conventional beamformer, suffering from frequency variation. Instead, a frequency invariant beamformer (FIB) is employed. We further show that the compensation filter of the FIB can actually be approximated by Hankel function of the first kind, simplifying the calculation of the FIB.