Experimental Testing of a Nonredundant Spherical Spiral NFFF Transformation for Offset Mounted Quasi-planar AUTs

This communication deals with the experimental validation of an accurate nearfield-far-field (NFFF) transformation technique with spherical spiral scanning for offset mounted quasi-planar antennas, which, unlike the classical spherical one, requires a number of NF data minimum and coincident with that needed in the onset mounting case. This last feature makes such a NFFF transformation very attractive, since, when a centred mounting of antenna under test (AUT) is not possible, the number of NF data required by the classical spherical NFFF transformation considerably increases. Such a NFFF transformation exploits the nonredundant sampling representations of electromagnetic fields and has been attained by considering a quasi-planar antenna as enclosed in an oblate ellipsoid and applying the unified theory of spiral scannings for nonspherical AUTs. An optimal sampling interpolation formula allows the fast and precise recovery of the NF data required by the classical spherical NFFF transformation from the collected nonredundant ones. Some experimental results, which assess the efficacy of the developed technique, are shown, thus confirming its validity also from the practical viewpoint.