Far-field reconstruction from probe compensated helicoidal near-field measurements

Measurement techniques in the antenna near-field (NF) region play a significant role in the evaluation of far-field (FF) patterns. The complexity and cost of the measurement set-up, as well as the time needed for data acquisition, can be reduced by means of a continuous and synchronous movement of the probe and antenna-under-test (AUT). The acquired NF voltage data are then used to recover the data needed by the classical probe compensated NF-FF transformation with cylindrical scanning. Helicoidal scanning is obtained by means of a rotation of the AUT and a linear movement of the probe. Since a uniform helix makes an infinite number of rounds along the cylindrical surface, the overall number of samples needed to represent the probe voltage on the cylinder becomes unbounded when the scanning surface approaches infinity. On the other hand, the overall number of samples remains always finite when a nonuniform helix is considered. As a consequence, helicoidal scanning employing a nonuniform helix requires a significantly reduced number of data in any practical case. The paper develops an algorithm which makes use of the appropriate sampling functions, thus allowing a more efficient recovery of the probe voltage on the cylinder from its samples on a nonuniform helix.