Field characterisation of an aircraft sized TEM cell

DSTO conducts research into novel approaches for aircraft HIRF (High Intensity Radiated Fields) testing with recent work focused on testing at frequencies below 30 MHz. A 30 m × 11 m × 6 m reverberation chamber, developed as part of our research program, has been modified to incorporate a TEM (Transverse electromagnetic) mode of operation, with a 20 m × 6 m septum as the major component. The ultimate aim is to provide continuity in the available testing frequencies between the TEM and reverberation modes of operation. A validated computational model of the system has been used to investigate the uniformity of the electric field and the power requirements as a function of frequency. Results indicate that below 15 MHz, where pure TEM modes of operation are achievable, field variations of no more than 6 dB are observed over the volume occupied by a representative EUT (equipment under test). In addition, the power required to achieve a field strength of 200 V/m is of the order of 20 kW. Also discussed in this paper, is that at resonant frequencies within the chamber, the situation becomes uncertain and requires further investigation.