Abstract
A direct near-field-far-field transformation with helicoidal scanning is developed. It is based on the nonredundant sampling representation of electromagnetic fields and uses a spherical antenna modelling to determine the number of helix turns. Moreover, the number of voltage samples on each of them is fixed by the maximum transverse dimension of the antenna, both to simplify the mechanical scanning and to reduce the computational effort. This technique allows the evaluation of the antenna far field directly from a minimum set of near-field data without interpolating them. Although the number of near-field data employed by the developed technique is slightly increased with respect to that required by rigorously applying the nonredundant sampling representation on the helix, it is still remarkably smaller than that needed by the standard near-field-far-field transformation with cylindrical scanning. The effectiveness of the technique is assessed by numerical and experimental results.
Highlights
The techniques for the reconstruction of antenna radiation patterns from near-field (NF) measurements have been widely investigated and used for applications ranging from cellular phone antennas to large-phased arrays and complex multibeam communication satellite antennas [1,2,3,4,5]
Optimal sampling interpolation (OSI) formulas of central type [16] have been employed to efficiently recover the data required by the corresponding NF-FF transformation from the knowledge of the acquired nonredundant ones
The approach in [10] has been reviewed in order to match the advantages of the direct cylindrical NF-FF transformation with those own of the fast helicoidal scanning
Summary
The techniques for the reconstruction of antenna radiation patterns from near-field (NF) measurements have been widely investigated and used for applications ranging from cellular phone antennas to large-phased arrays and complex multibeam communication satellite antennas [1,2,3,4,5]. A probe uncompensated NF-FF transformation technique with planar spiral scanning has been proposed in [29], to efficiently evaluate the antenna far field directly from the acquired NF data It uses the convolution property of the radiation integral and the fast Fourier transform (FFT) algorithm to determine the antenna far-field pattern without requiring any interpolation step. Since such an approach does not exploit the nonredundant representations of EM fields, it needs a useless large amount of measurements. A direct NF-FF transformation with cylindrical scanning, based on the aforementioned nonredundant sampling representations, has been developed in [10] It allows the evaluation of the antenna far field in any cut plane directly from the nonredundant NF data without interpolating them. The number of helix turns is determined by the nonredundant sampling representation along a generatrix which makes use of the spherical AUT modelling, whereas the voltage samples on each of them is fixed by the AUT maximum transverse dimension
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