Currents Induced on Conducting Rods by Near and Far Zone Sources

Missies in flight are often immersed in an elec­ tromagnetic environment. Whether desirable or not, this EMC situation may cause undue influences on per­ formance of on-board subsystems. To measure these effects, it invariably becomes necessary to experimen­ tally test real-life systems on an antenna range. To cover all threats, large frequency bands as well as high field intensities are needed. Thus the use of near-zone transmitting antennas are often required. The simulation validity of such a test arrangement is a cause for concern, since in flight, the missile experiences plane wave incidence. Are there then significant differences in system response when caused by the near-zone source fields compared to plane wave fields? More importantly, how far away does the source have to be to achieve valid simulation? Since the cost of the test facility depends directly on the power needed, which in turn depend on the separation distance, the answers to these questions are therefore of cri­ tical concern.