EMC test site validations for 1m automotive and military emissions tests

Computational Electromagnetic Simulation holds promise as a way of validating EMC test setups and has been investigated by numerous researchers already. By producing a simulation of a reference emission source, it is hoped that an “ideal” set of measurement results can be simulated; then, if a particular test site such as an Absorber Lined Shielded Enclosure (ALSE) can produce measurement results that are consistent with the simulation results within some limit, the chamber can be considered to be sufficiently free of unwanted reflections. Standards that could benefit from such a set of validation criteria are CISPR 25, MIL STD 461 and RTCA/DO-160: these three methods employ 1m range tests using a conductive table top, generally in a semi-anechoic chamber (although an OATS is sometimes used). In all three cases, a monopole antenna is used for radiated emissions tests below 30 MHz. A special challenge that is associated with this endeavour is the existence of a resonance in the frequency range 10-30 MHz with the conductive table top and active monopole antenna. This is well identified and changes introduced with MIL STD 461 version F over version E are designed to address the resonance. This paper describes simulations that were performed to investigate the different variations on rod antenna tests in the range 100 kHz to 30 MHz.