Far-field pattern reconstruction directly from a minimum number of helicoidal near-field data

In this work, we propose a direct near-field - far-field transformation with helicoidal scanning, suitable for elongated antennas. Such a technique, based on the nonredundant sampling representation of electromagnetic fields, uses a flexible source modelling of the antenna under test to determine the number of the helix turns and the minimum cylinder rule, as in classical cylindrical scan, to fix the number of data on each of them. It is so possible to evaluate the antenna far field in any cut plane directly from the acquired helicoidal near-field data without interpolating them. Numerical and experimental tests assessing the effectiveness of the approach are shown.