Chapter 19: Calibration of ELF to UHF Wire Antennas, Primarily for EMC Testing

19.1 Introduction

Wire antennas such as monopoles, biconical and log-periodic dipole array (LPDA) antennas are used for electromagnetic compatibility (EMC) testing, and typically, cover the frequency ranges 1 kHz to 30 MHz, 30-300 MHz and 200 MHz to 2 GHz, respectively. The primary parameter of interest is the maximum gain. EMC implies that the radiated emission from a product does not impair the performance of a 'victim' product, so that, for example, a radio and television set will operate satisfactorily when placed next to each other. It is useful to know the strength of the E-field that one product is 'bathing' the other product in. For this reason the antenna gain is given in terms of antenna factor (AF) which enables a direct conversion to E-field magnitude. Uncertainties for EMC-radiated emission measurements tend to be of several decibels; therefore, the AF data are generally not needed to uncertainties better than 0.5 dB. The antenna return loss is usually measured during the calibration of AF so that the mismatch uncertainty of the receiver reading during an EMC test can be estimated.

Above 30 MHz, EMC measurements are made with the antenna both vertically and horizontally polarised so the cross-polar discrimination of the antenna is required as a component of the uncertainty budget. EMC measurements below 1 GHz are made over conducting ground planes or in free-space environments, either outdoors or in an anechoic chamber, whose imperfections will be 'seen' according to the directivity of the antenna, so knowledge...