Antenna directivity evaluation by planar spiral scanning

An efficient approach is here presented for the evaluation of the antenna directivity from a nonredundant number of near-field measurements on a planar spiral. It can be applied whenever the power radiated by the antenna in the backward half-space is negligible and the total radiated power coincides practically with that radiated in the forward one. It makes use of a closed form formula for computing the total radiated power from the knowledge of the radiation intensity samples on the far-field sphere. These samples are determined via a probe compensated near-field - far-field transformation from measurements collected on a planar spiral and by properly using an optimal sampling interpolation formula. Numerical tests assessing the effectiveness of the proposed procedure are reported