Comparison of active levelling and pre-calibrating/substitution method for radiated immunity testing of large equipment

Radiated susceptibility tests have originally been performed using the so-called leveling method: a field strength sensor is put in front or on top of the equipment under test and the power towards the antenna is changed until the required level is achieved. Since computers became available for controlling test equipment the pre-calibration, or substitution, method became more popular. From a metrology point of view this is also a standard method but the leveling method is still preferred in some standards. The advantages and disadvantages of the methods are described in terms of the testing of very large equipment. Measurements were carried out with large and small equipment and the result shows that the methods are applicable for different purposes; Active leveling is more suitable for small EUT in closer distance while the pre-calibration is the established and preferred method for large equipment.