The accurate calibration of EMC antennas in compact chambers — Measurements and uncertainty evaluations

The accurate knowledge of the antenna factor is a fundamental requirement for reliable electromagnetic compatibility (EMC) measurements in emissions, immunity and human exposure tests. According to international standards, the calibration of EMC antennas requires close-to-ideal test sites (or calibration test sites), characterized by very large sizes of the ground plane and of the empty space volume above it (free-space behaviour). On the other hand a great number of EMC test sites are available and designed for measurements at 3m distance, therefore it would be very convenient to calibrate antennas in such facilities at the cost of an acceptable loss of accuracy. In this paper, the authors investigate the suitability of compact semi-anechoic chambers (standard chambers, compliant for measurements at 3 m distance from the equipment under test) for reliable antenna factor calibrations. As an application, the calibration of a common broadband biconical antenna in the 200–1000 MHz frequency range is here considered and analysed. A detailed experimental analysis is offered for estimating all the relevant uncertainty contributions.