Far-field evaluation directly from helicoidal near-field data

A direct near-field - far-field transformation with helicoidal scanning for electrically long antennas is proposed. It 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 maximum transverse dimension of the antenna to simplify the mechanical scanning and to reduce the computational effort. It allows the evaluation of the antenna far field directly from the acquired helicoidal near-field data without interpolating them. Numerical tests assessing the effectiveness of the approach are reported.