Abstract
An overview of the near-field-far-field (NF-FF) transformation techniques with innovative spiral scannings, useful to derive the radiation patterns of the antennas commonly employed in the modern wireless communication systems, is provided in this paper. The theoretical background and the development of a unified theory of the spiral scannings for quasi-spherical and nonspherical antennas are described, and an optimal sampling interpolation expansion to evaluate the probe response on a quite arbitrary rotational surface from a nonredundant number of its samples, collected along a proper spiral wrapping it, is presented. This unified theory can be applied to spirals wrapping the conventional scanning surfaces and makes it possible to accurately reconstruct the NF data required by the NF-FF transformation employing the corresponding classical scanning. A remarkable reduction of the measurement time is so achieved, due to the use of continuous and synchronized movements of the positioning systems and to the reduced number of needed NF measurements. Some numerical and experimental results relevant to the spherical spiral scanning case when dealing with quasi-planar and electrically long antennas are shown.
Highlights
The design of the modern antenna systems, integrated on portable devices or employed in radio base stations, requires the experimental verification of the antenna performances in terms of frequency bands and radiation diagrams
This paper provides a comprehensive overview of the nonredundant NF-FF transformations using fast spiral scanning techniques, which allow a drastic time saving, since they are realized through continuous and synchronized movements of the positioning systems and require a reduced number of NF measurements
The authors have first recalled the results on the nonredundant representations of EM fields, which constitute the theoretical background of the spiral scanning techniques
Summary
The design of the modern antenna systems, integrated on portable devices or employed in radio base stations, requires the experimental verification of the antenna performances in terms of frequency bands and radiation diagrams. It must be stressed that the use of effective AUT modellings when dealing with elongated or quasi-planar antennas offers, besides the reduction of the number of required NF data, another great advantage in the helicoidal and planar spiral scanning case, respectively It makes possible the consideration of measurement cylinders (planes) with a radius (distance) smaller than one-half of the antenna maximum size, reducing the error related to the truncation of the scanning surface.
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