Experimental testing on a near-field to far-field tranformation with planar spiral scanning for quasi-planar antennas

An efficient near-field - far-field (NF-FF) transformation with planar spiral scanning particularly suitable for quasi-planar antennas is experimentally validated. It relies on a nonredundant sampling representation of the voltage measured by the probe, obtained by applying the unified theory of spiral scan for nonspherical antennas and assuming that the antenna under test is enclosed in a surface formed by two circular bowls with the same aperture, but eventually different bending radii to fit better its geometry. An optimal sampling interpolation expansion is applied to effectively reconstruct the NF data needed by the standard plane-rectangular NF-FF transformation from the nonredundant ones acquired along the spiral. It is so possible to get a significant measurement time saving due to both the reduced number of required NF data and the exploitation of continuous and synchronized movements of the positioning systems. Experimental tests, carried out at the Antenna Characterization Lab of the University of Salerno and assessing the effectiveness of the NF-FF transformation technique, are reported.