Calibration of Antenna for EMI Measurements in Compact Semi-anechoic Rooms

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, this would imply calibrating antennas in close-to-ideal test sites (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 the greater number of EMC test sites is designed for measurements at 3 meters 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 on the suitability of compact (standard compliant for measurements at 3 m) semi-anechoic rooms for reliable antenna factor calibrations of EMI antennas. As an example, the calibration of a common broadband biconical antenna in the range 200 MHz-1 GHz has been considered. A detailed experimental analysis was performed for estimating all the involved uncertainty components.