The use and calibration of small dipole and loop antennas

In general, electronic equipment radiates electromagnetic waves. In some cases it is designed to do so, but in the majority of cases it is not and this radiation can cause interference with other electronic equipment. So it is necessary to test the equipment for electromagnetic compatibility (EMC) with neighbouring equipment. The parameter commonly required of a radiation (or emission) test is a measure of the radiated power in the far-field. However, a true measure of the electric (E) or magnetic (H) fields in the far-field is only directly obtainable when the receiving antenna (probe)is a few wavelengths away from the equipment under test (EUT). It is for this condition that a receiving antenna is normally calibrated, that is, its voltage output is directly related to the far-field strength. Results of E-field measurements on a spherical dipole in a range of TEM cells is presented, with an analysis of uncertainties of measurement due to the proximity of reflecting surfaces. The uncertainty of measurement of loop antennas in TEM cells is also presented