Experimental Testing on an Effective Technique to Reconstruct the Far- Field Pattern of a Long Antenna from Near-Field Measurements Acquired via Spherical Spiral Scan

In this paper, the experimental validation of a fast and accurate near-field – far-field (NF–FF) transformation with spherical spiral scanning for elongated antennas is provided. Such a transformation relies on a nonredundant sampling representation of the voltage measured by the probe, obtained by using the unified theory of spiral scans for nonspherical antennas and adopting a cylinder ended in two half-spheres to model long antennas. It allows a remarkable reduction of the measurement time due to the use of continuous and synchronized movements of the positioning systems and to the reduced number of needed NF measurements. In fact, the NF data required by the classical spherical NF–FF transformation are efficiently and accurately recovered from those collected along the spiral, by using an optimal sampling interpolation expansion. Experimental results, obtained at the Antenna Characterization Lab of the University of Salerno and assessing the effectiveness of such a NF–FF transformation, are shown.