Comparisons of Pattern Measurements from Two Near-Field Systems

Antenna patterns are perhaps the most difficult parameter to measure accurately. The measurement accuracy is often contentious, including basic repeatability. The power gain, or else the co-polarized power gain, in the expected maximum direction is usually the focus of an accuracy specification, following a tradition of point-to-point free-space links. It follows that for a specification of measurement accuracy, many antennas or systems are characterized by maximum gain only. For accurate link budgets, the in-situ total gain is the most important, but time-varying scatterers in or near the Fresnel zone, - and for long-distance links, varying refraction - can introduce time-variations in a direct measurement. The estimation accuracy of a direct measurement is at its best for maximum gain because this has the maximum SNR. But complete patterns are also important, and the preferred measurement approach is via the near-fields, despite the pattern parameters, such as maximum directivity, being estimated indirectly. Various correlations of the patterns can provide useful information about the complete patterns (or selected portions of them), including an indication of measurement repeatibility. This paper presents gains and pattern correlations of pattern measurements from two professional-grade systems which have similar, but not identical, configurations. The results provide a feel for the pattern repeatability from using compatible professional-grade measurement systems, and realworld factors including different operators and procedures. The testing antenna is a simple low-gain dual patch antenna.