Experimental validation of the SVD based approach to compensate the positioning errors in a nonredundant spherical NF–FF transformation

An efficient near-field – far-field (NF–FF) transformation with spherical scanning for long antennas, requiring a minimum number of irregularly spaced data, is experimentally validated in this work. It is based on a nonredundant sampling representation of the voltage measured by the probe, obtained by assuming the antenna under test as enclosed in a prolate ellipsoid, a modelling particularly suitable for electrically long antennas. The singular value decomposition method is employed to recover the NF data at the points fixed by the sampling representation from the acquired nonuniformly distributed ones, which are assumed to lie on irregularly spaced parallels. Once the uniform NF data have been reconstructed, those needed by the classical spherical NF–FF transformation are efficiently evaluated by an optimal sampling interpolation formula. Some experimental results, performed at the Antenna Characterization Lab of the University of Salerno and assessing the effectiveness of such a technique for compensating known positioning errors, are shown.