Sources of variability in semi-anechoic chamber radiated emissions measurement

Investigations into the sources of variability in radiated emissions testing to CISPR 25 were conducted in a 6.7 m×3.7 m×3.2 m semi-anechoic chamber. A large number of potential sources of variability were identified and experiments conducted to quantify the level of variability each potential source introduced to the measurement of radiated emission. A commercial wide-band comparison noise emitter (CNE) was used as an emission source. Three different receiving antennas (biconical, log-periodic-biconical and horn) were used to assess some of the emission variability due to different antenna structures. Other elements of variability examined include cable placement, effect of detector type and positional accuracy. It is believed that this is the first reported quantified analysis of the effect of many of the investigated variables on radiated emission levels in a compact chamber. This study should enable higher precision results in semi-anechoic chamber radiated emission tests by appropriate control of emission variability within the test environment. Ultimately the data could improve specification writing for EMC radiated emissions testing