Experimental tests on a spherical near-field to far-field transformation using a reduced number of offset NF data

This work provides the experimental assessment of an effective probe-compensated near-field to far-field transformation (NFFFT) technique with spherical scanning for offset mounted quasi-planar antennas, requiring a number of NF data minimum and equal in both the cases of onset and offset mounting. The interest for this NFFFT is due to the fact that it may be not possible, for practical constraints, a mounting of the antenna under test (AUT) centred on the scanning sphere centre. In such a case, the number of NF data required by the standard spherical NFFFT grows considerably owing to the increase of the radius of the minimum sphere containing the AUT. Conversely in the developed NFFFT, these NF data are accurately reconstructed from the nonredundant acquired ones by applying a two-dimensional optimal sampling interpolation expansion, thus allowing to get a remarkable measurement time saving. The sampling expansion is based on an effective representation of the voltage detected by the scanning probe achieved by properly applying to it the nonredundant sampling representation of electromagnetic field and considering the AUT as contained in an oblate spheroid.