Characterization of real-world steered-beam antennas from amplitude-only near-field data

Phase-less near-field techniques are becoming increasingly more important for antenna characterization, due to the growing interest in millimeter-and sub-millimeter-wave applications, where the near-field phase is difficult or even impossible to measure. In this framework, the routine application of phase-less near-field/far-field (NFFF) transformations to real-world operational antennas is a challenging problem, recently questioned in the literature, requiring algorithms capable of providing reliable and accurate results over a large class of radiators. In the present paper, the possibility of applying phase-less near-field techniques for routine testing of antennas is discussed. We point out how -following the recent developments in the field, and by a formulation of the problem based on proper representations of unknowns and data - it is possible to gain the reliability and the accuracy required for this. Experimental tests were carried out on steered-beam antennas, which have lately been pointed out as "difficult" workbenches, to test the feasibility of operational phase-less near-field/far-field transformations. The experimental results refer to a reflectarray radiating a tilted beam, and to a phased array of large electrical dimensions, radiating a scanned beam and actually employed in real-world applications.