Positioning errors compensation in the NF - FF transformation with helicoidal scanning for long antennas: experimental tests

An effective technique to compensate the positioning errors in a near-field - far-field (NF-FF) transformation with helicoidal scanning for long antennas is presented and experimentally validated. It relies on a nonredundant sampling representation of the probe voltage obtained by considering the antenna as enclosed in a cylinder ended in two half-spheres and employs an iterative scheme to reconstruct the helicoidal NF data at the points fixed by the representation from the acquired irregularly spaced ones. Once the helicoidal data have been retrieved, those needed by a standard NF-FF transformation with cylindrical scan are efficiently evaluated by using an optimal sampling interpolation algorithm. The comparison of the FF patterns reconstructed from the irregularly spaced measurements with those obtained from the data directly acquired on the classical cylindrical grid assesses the effectiveness of the approach.