Far-Field Reconstruction From Near-Field Data Acquired via a Fast Spherical Spiral Scan: Experimental Evidences

Abstract

Abstract-A probe-compensated near-field-far-field (NF-FF) transformation with spherical spiral scanning, which makes possible to lower the number of needed measurements, as well as the time required for the data acquisition when characterizing quasi-planar antennas, is experimentally verified in this paper. Such a technique, based on the nonredundant representation of electromagnetic fields, has been achieved by properly applying the unified theory of spiral scans for nonspherical antennas and adopting a very flexible source modelling, formed by two circular "bowls" with the same aperture diameter but different bending radii. A two-dimensional optimal sampling interpolation formula allows one to reconstruct the NF data at any point on the measurement sphere and, in particular, at those required by the classical NF-FF transformation with spherical scanning. The reported NF and FF reconstructions, obtained from the nonredundant samples acquired on the spiral, assess the accuracy of the proposed technique.

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

“…It is worth noting that these reduction percentages are much greater than the corresponding ones obtained in [29], wherein the two-bowls modelling was adopted to shape a quasi-planar antenna. This result does not depend on the particular antennas considered in these two papers, but is a general validity result: the time saving obtainable by using the appropriate spiral scanning technique when considering long antennas is usually remarkably greater than that in the quasi-planar antennas case.…”

“…1). The effectiveness of that for quasi-planar antennas using the two-bowls modelling has been already assessed in [29]. Also in such a case, the testing has been carried out by means of the spherical NF facility available in the anechoic chamber of the Antenna Characterization Lab of the University of Salerno and has wholly confirmed the effectiveness of this innovative transformation, which allows a remarkable time saving without losing the accuracy of the classical spherical one.…”

“…Innovative NF-FF transformation techniques with spherical spiral scanning have been proposed in recent years [22][23][24][25][26][27][28][29]. They maintain the interesting features of those employing the spherical scanning and, what's more, reduce in a remarkable way the time required for the NF data acquisition, which, as suggested in [30], is performed on fly by exploiting continuous and synchronized movements of the positioning systems of the probe and AUT.…”

“…In a first approach, the sampling representation has been determined [22][23][24] by adopting a spherical source modelling, i.e., by considering the AUT as enclosed in the smallest sphere able to contain it. Then, by properly applying the unified theory of spiral scans for nonspherical antennas [25], NF-FF transformations with spherical spiral scanning for elongated or quasi-planar antennas have been developed in [26][27][28][29], thus avoiding the useless increase in the number of the NF data to be acquired, related to the use of the spherical modelling when considering these kinds of antennas. More in detail, an oblate [26,28] and a prolate ellipsoid [26] have been employed to shape a quasi-planar and an elongated antenna, respectively.…”

“…More in detail, an oblate [26,28] and a prolate ellipsoid [26] have been employed to shape a quasi-planar and an elongated antenna, respectively. As an alternative, a quasi-planar antenna has been considered as enclosed in a surface formed by two circular bowls with the same aperture diameter but eventually different lateral bends [27,29] and a rounded cylinder, namely, a cylinder ended in two half-spheres has been adopted for modelling an elongated AUT [27]. Generally, the use of these last modellings results to be more effective from the data reduction viewpoint with respect to the employment of the corresponding ellipsoidal ones, since they allow a better fitting of many antennas by properly setting their geometric parameters.…”