An iterative technique to compensate for positioning errors in the NF - FF transformation with helicoidal scanning for long antennas

An effective procedure is developed in this paper to compensate the probe positioning errors when using a near-field to far-field transformation technique with helicoidal scanning for long antennas. It is based on a prolate ellipsoidal modelling of the antenna under test and makes use of an iterative scheme to retrieve the uniformly distributed helicoidal near-field data from the irregularly spaced acquired ones. Once these data have been recovered, those required to perform a standard near-field--far-field transformation with cylindrical scanning are efficiently determined via an optimal sampling interpolation algorithm. Some numerical tests are reported to assess the accuracy of the approach and its robustness with respect to random errors affecting the data. At last, the validity of the developed technique is further confirmed by the experimental tests performed at the Antenna Characterization Lab of the University of Salerno.