Possible improvement of the correlation method for GTEM cell emission tests

The standard IEC 61000-4-20 describes the test procedures in coaxial transmission lines, including a so called correlation method, in order to compare emission test results measured in a GTEM cell with the limits given by the product standard. One parameter that has to be taken into account is the directivity of the test object, characterizing its radiation pattern. The standard assumes a constant and frequency-independent value for it. This leads to significant deviations in the emission spectrum compared to a measurement taken inside a semi-anechoic chamber (SAC), as was observed for real-world objects. The following paper describes a new approach to improve the correlation method based on a frequency-dependent directivity retrieved from a numerical calculation of three more or less complex electrical objects.