Evaluation of the far field radiated by long antennas directly from data acquired through a fast helicoidal scanning

A direct near-field - far-field transformation with helicoidal scanning for electrically long antennas is proposed in this paper. Such a transformation, which allows the evaluation of the antenna far field in any cut plane directly from the acquired near-field data without interpolating them, relies on the nonredundant sampling representation of electromagnetic fields and makes use of a prolate ellipsoidal modelling of the antenna under test for determining the number of helix turns, whereas the number of samples on each of them is fixed by the minimum cylinder rule, as in the classical cylindrical scan. Numerical and experimental tests assessing the effectiveness of the approach are shown.