Relations between radiation characteristics of small antennas located in free space and close to lossy phantom

The characterization of small terminal antennas close to head phantoms and other lossy objects is time-consuming, and in particular if the radiation patterns are to be measured for many positions close to the phantom. The main effect of a lossy object is absorption and a corresponding reduction in the radiation efficiency of the antenna. For operation in multipath environments with Rayleigh fading the radiation efficiency is the most significant performance parameter; the radiation pattern plays a minor role. Therefore, characterization could be based on only the radiation efficiency, which can be measured fast and accurately in e.g. a reverberation chamber. It has been proposed (and is also practiced some places) to determine the absorption in the head phantom and the corresponding radiation efficiency by simply using the free space radiation pattern to calculate the relative power shadowed by the phantom. The purpose of the present work is to investigate the relevance and accuracy of such an approach, compared to an actual measurement of radiation efficiency