Some measurements of field uniformity within commonly used environments for radiated susceptibility measurements

Measurements of field strength are made in a 7×7×7 array of positions within a 50 cm cubic volume, in eleven environments that are commonly used for radiated susceptibility testing. The average value, absolute variation and standard deviation of the fields are analysed to deduce the field uniformity levels in each environment for the frequency range of 30-230 MHz. A simulated item of equipment under test is also used to assess the suitability of each environment for making repeatable measurements. It is concluded that semi-anechoic chambers offer the best environment in which to perform susceptibility measurements, but that stripline cells used in small damped screened rooms can offer a similar level of repeatability. A criterion, that the standard deviation of the fields over the volume occupied by the equipment under test should be at least 13 dB down from the mean field, is proposed for a general environment to provide repeatable measurements