The definition of the EMC antenna calibration time intervals

The calibration of EMC antenna has always been a frustrating subject for most EMC laboratories. On the other hand in many cases EMC antennas are recalibrated when it is not strictly necessary. This paper proposes a procedure to establish when EMI antennas shall be calibrated on the basis of technical considerations without making reference to abstract quality assurance rules. It seems more correct to stipulate the definition of the calibration time intervals on the basis of a statistical approach comparing the past performance characteristics with the present ones. The reflection coefficient at the antenna input terminal is monitored over the frequency range of interest at regular time intervals to detect whether a modification has occurred; only if this modification is beyond the assumed tolerance limits the antenna shall be calibrated. The procedure illustrated in this paper is in line with the well accepted use of control charts described in quality assurance documents; it has been modified from the standard methods to take into account the specific characteristics of EMI antennas.