Nonredundant spherical spiral NF/FF transformation accounting for an offset mounting of an electrically large quasi-planar AUT

This work concerns the development of an efficient near-field/far-field (NF/FF) transformation technique with spherical spiral scanning suitable for an offset mounted quasi-planar antenna. Such a NF/FF transformation, relying on the nonredundant sampling representations of electromagnetic fields, requires practically the same number of NF data both when the antenna under test (AUT) is onset and offset mounted, since such a number depends only on the surface modelling the AUT. It is developed by properly applying the unified theory of spiral scannings for non-volumetric antennas, when the AUT is considered as contained in a flexible surface formed by two circular bowls with the same aperture and eventually different bending radii. Some numerical results assessing the accuracy and the robustness of the proposed technique are shown.