A broadband compact range for radiative EMC testing

Ideally, radiative EMC tests (including the calibration of field probes) should be performed under `far-field´ conditions, requiring a relatively large distance between the equipment under test (EUT) and the known antenna. Such far-field conditions would give repeatable results that would allow straightforward prediction of the EMC behaviour of the EUT in a real situation. Unfortunately, such tests are not feasible since, in susceptibility mode, they would require high-power variable-frequency radiation that would breach frequency allocation regulations. Analogously, the results of a far field emission test could be masked by external noise. A number of procedures (screened rooms, mode-stirred chambers, TEM cells, etc.) are used to undertake such tests at present, but the test conditions in all of these deviate substantially from those in the far field. The compact range, however, is a test procedure now well established in the antenna community, which enables an approximation to a plane wave to be set up very close to a suitable aperture antenna, thus enabling far field conditions to be realised in a compact space. It also permits efficient use of transmitted power in a susceptibility test and any stray radiation may be easily absorbed by anechoic material. The experimental range constructed at Bradford University is outlined