Influence of calibration and measurement techniques on the inhomogeneity of electromagnetic fields for immunity tests

The influence of varying calibration procedures with different measurement hardware on the quality of electromagnetic test fields for immunity tests of electronic equipment is considered. Field variations up to 3 dB are quite common and in case of test hall resonances even more than 10 dB can occur. Reasons for these deviations can be found in the calibration procedure, the environment of the test setup, and mainly in the field generator. Here, not completely suppressed reflections of the electromagnetic waves at the inner wall(s) of the field generator (anechoic chamber or (G)TEM-cell) and different types of field sensors (isotropic or directional) play important roles. Polarization ellipses are sensitive visual representations to assess residual field inhomogeneities