NF-FF transformation technique with nonuniform helicoidal scanning

As well known, the use of near field - far field (NF-FF) transformation techniques, for determining antenna patterns from the knowledge of NF data, allows one to overcome those drawbacks which make unpractical to perform such measurements on a conventional FF range. Moreover, the development and the spreading of NF-FF transformation techniques employing planar, cylindrical or spherical scanning systems is justified from the fact that each approach has its own particular advantages and limitations. In this context, as suggested in [1], [2], a continuous movement of the positioning systems of the probe and of the antenna under test (AUT) permits to reduce complexity and cost of the measurement set-up, as well as the time needed for data acquisition. In particular, with reference to the innovative (uniform) helicoidal scanning proposed in [2], a nonredundant sampling representation of the electromagnetic field over a circular helix with constant step in z has been developed. The corresponding interpolation algorithm has resulted to be fast, accurate and stable, so that it can be employed to reconstruct the field over the considered cylinder in the NF region at any point required by the cylindrical NF-FF transformation techniques available in literature.