Effects of a Non-Ideal Plane Wave on Compact Range Measurements
Authors: David Wayne, Jeffrey A. Fordham, John McKenna
Performance requirements for compact ranges are typically specified as metrics describing the quiet zone's electromagnetic-field quality. The typical metrics are amplitude taper and ripple, phase variation, and cross polarization. Acceptance testing of compact ranges involves field probing of the quiet zone to confirm that these metrics are within their specified limits. It is expected that if the metrics are met, then measurements of an antenna placed within that quiet zone will have acceptably low uncertainty. However, a literature search on the relationship of these parameters to resultant errors in antenna measurement yields limited published documentation on the subject.
Various methods for determining the uncertainty in antenna measurements have been previously developed and presented for far-field and near-field antenna measurements. An uncertainty analysis for a compact range would include, as one of its terms, the quality of the field illuminating on the antenna of interest. In a compact range, the illumination is non-ideal in amplitude, phase and polarization. Error sources such as reflector surface inaccuracies, chamber-induced stray signals, reflector and edge treatment geometry, and instrumentation RF leakage, perturb the illumination from ideal.
This paper will review, in a summary fashion, the equations that estimate the effect of a non-ideal incident electromagnetic field on an antenna. It will calculate the resulting antenna pattern for a candidate antenna and compare it to the ideal antenna pattern thus showing the induced errors. Parametric studies will be presented studying the error effects of varying illumination metrics on the antenna measurement. In addition, measured field probe data from a compact range will also be used with the candidate antennas to investigate induced errors.
The intent is to provide the reader with insight as to how the typical compact range metrics affect the accuracy of an antenna measurement. This work is intended to be the foundation for future work to develop a comprehensive uncertainty analysis for compact range measurements.