A Novel Far-Field Transformation via Complex Source Beams for Antenna Near-Field Measurements on Arbitrary Surfaces

This paper presents a general technique for an efficient and accurate near-field (NF) to far-field (FF) transformation based on the complex source beam (CSB) method. This CSB-based NF–FF transformation is applicable to all three conventional NF measurement techniques, namely, to the planar, cylindrical, and spherical as well as to an arbitrary measurement surface. In this technique, a set of CSBs launched radially out from the antenna under test (AUT) is used to represent its NF. The weights of these CSB radiation basis functions are found by matching them to the measured AUT NF on the measurement surface. Once the CSB weights are found, the same CSBs remain continuously valid everywhere from NF to FF. It is noted that due to the occurrence of a natural Gaussian-like field taper away from each beam axis, only a relatively few CSBs are typically needed to represent the AUT fields at any point in its far zone in comparison to the conventional plane wave or vector wave function expansions for a given size of AUT. The remaining CSBs can be discarded with negligible error. This property among a few others leads to some advantages over conventional NF–FF methods.