Biased Estimation of Antenna Radiation Efficiency Within Reverberation Chambers Due to Unstirred Field: Role of Antenna Stirring

Reverberation chambers (RCs) are now a reliable alternative to anechoic chambers (ACs) to perform antenna radiation efficiency measurements. Most methods, including the two-antenna one used in this article, are based on the evaluation of the stirred components of the scattering parameters. They are obtained by subtracting the average scattering parameters from the measured ones. This averaging is performed because of mechanical stirring, that is, sometimes supplemented by additional stirring such as antenna stirring (which includes platform stirring and source stirring). In this article, we present an extensive study on the role of antenna stirring in the retrieved radiation efficiency. Four measurement campaigns were successively performed: without antenna stirring, with platform stirring only, with source stirring only, and with a combined stirring of both antennas. Performing only source stirring or platform stirring leads to a biased estimation of the radiation efficiency. Therefore, we showed that the stirring of both antennas is mandatory to obtain an unbiased estimation of the radiation efficiency.