Far-Field Pattern Evaluation From Data Acquired on a Spherical Surface by an Inaccurately Positioned Probe

This letter concerns the experimental validation of two effective techniques allowing the compensation of known positioning errors in a nonredundant spherical near-field-far-field (NF-FF) transformation, using an oblate ellipsoid to shape quasi-planar antennas. The former uses the singular value decomposition method to evaluate the NF data at the points fixed by the nonredundant sampling representation from the irregularly distributed ones, and can be applied when the nonuniformly spaced samples lie on nonuniform parallels. The latter, adopting an iterative technique, can be used even if such a hypothesis does not hold, 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 evaluated via an optimal sampling interpolation algorithm.