Comparison method for validation of radiated emission test site

Summary form only given. As per ANSI C 63.4-1992, a Radiated Emission Test Site (RETS) shall be considered acceptable for radiated electromagnetic field measurements if the measured Normalized Site Attenuation (NSA), are within +4 dB of the theoretical NSA for an ideal site for both horizontal and vertical polarizations. ANSI C 63.4-1992 allows +4 dB NSA tolerance, which includes antenna/instrumentation calibration errors, measurement technique errors, and errors due to site anomalies. These errors are analyzed in ANSI C 63.6-1988, wherein it is shown that more than 50% of the total allowable tolerance is contributed by the antenna factors of the transmit and receive antennas used and the performance of a well-built site contributes only 1 dB. Experience has shown that antenna factor variations may be caused by the antenna height variations and polarization changes with respect to the ground plane, the use of measurement geometries, mutual coupling, and transmission line scattering for vertically polarized antennas. Also, in ANSI C 63.4-1992, a single-point NSA measurement is carried out which is insufficient to pick up all possible reflections from the site very accurately. In this paper a new methodology is proposed called the "Comparison Method", in which the uncertainty in antenna factors used for SA measurements is avoided. In this approach, instead of a comparison of measured with theoretical "NSA" as given in ANSI C 63.4-1992, the RETS is validated by comparing the SA's measured at different locations without changing the antenna path geometry, because only one reflecting surface (metal ground plane) exists.