NF-FF transformation with uniform planar spiral scanning for volumetric antennas

An effective near-field-far-field (NF-FF) transformation, wherein the NF samples are collected over a plane through a planar spiral scan with uniform step, is proposed in this work. It is suitable for volumetric antennas and uses a reduced number of NF samples. A two-dimensional (2-D) optimal sampling interpolation algorithm, which makes possible to accurately reconstruct the NF data needed by the standard NF-FF transformation with plane-rectangular scanning from the acquired spiral samples, is then developed, by choosing the spiral step coincident with the sampling spacing needed to interpolate along a radial line, according to the spatial band-limitation properties of electromagnetic fields, and by arranging a proper nonredundant representation along such a spiral. Some numerical simulations assessing the accuracy of the developed 2-D OSI algorithm and the effectiveness of the FF reconstruction process are shown.