Experimental tests on an effective near-field to far-field transformation with spherical scan from irregularly spaced data

Two efficient techniques to compensate known positioning errors in a nonredundant spherical near-field – far-field (NF–FF) transformation, using a cylinder ended in two half-spheres for modelling long antennas, are developed and experimentally assessed in this communication. In order to evaluate the NF data at the points fixed by the nonredundant sampling representation from the acquired irregularly spaced ones, the former approach uses the singular value decomposition method and can be applied when the nonuniformly distributed samples lie on nonuniform parallels. The latter, based on an iterative technique, can be adopted even if such a hypothesis is not satisfied, but requires the existence of a biunique correspondence associating at each uniform sampling point the nearest nonuniform one. Once the uniform samples have been retrieved, those needed by the classical spherical NF–FF transformation are efficiently determined via an optimal sampling interpolation algorithm.