Nonredundant NF-FF transformation with spherical spiral scan for a non-centered quasi-planar antenna under test

An efficient near-field — far-field (NF-FF) transformation technique with spherical spiral scanning suitable for an offset mounted quasi-planar antenna under test (AUT) is proposed in this work. Such a NF-FF transformation, based on the nonredundant sampling representations of electromagnetic fields, practically makes use of the same number of NF data in the case of both the onset and offset AUT mountings, depending such a number only on the surface shaping the AUT. It has been developed by properly applying the unified theory of spiral scannings for non-volumetric antennas, when the AUT is considered as enclosed in the smallest oblate ellipsoid able to contain it. Some numerical results assessing the accuracy and the robustness of the proposed technique are shown.