Spiral Scannings Research Articles

Pattern Evaluation From NF Spherical Spiral Data in the Noncentered Quasi-Planar Antennas Case

The far-field reconstruction of noncentered quasi-planar antennas is here addressed by using a spherical spiral scan in the near-field region. A reduction of the near-field data is achieved by suitably exploiting the unified theory of spiral scannings for nonspherical antennas. Such a technique, relying on the nonredundant representation of electromagnetic fields, adopts an oblate spheroid as source modeling and uses a two-dimensional optimal sampling interpolation algorithm to recover the data needed to execute the classical near-field–far-field transformation. In this case, the reduction process is required since an inadequate mounting system increases the number of needed data when compared to facilities, which allow one to center the antenna under test with respect to the spherical scanning surface. The above-mentioned statement is based on the following rule: the classical near-field–far-field transformation requires a number of data depending on the smallest spherical surface, which encloses the antenna and shares the same center as the scanning surface. The reported results thoroughly prove the efficacy of the developed technique.

Fast and Accurate Antenna Pattern Evaluation From Near-Field Data Acquired via Planar Spiral Scanning

Two fast and accurate probe compensated planar spiral near-field–far-field (NF–FF) transformation techniques, using nonredundant NF data, are experimentally assessed. These techniques allow a remarkable measurement time saving since they require a reduced number of NF data, which are collected on fly by properly and continuously moving the positioners. They have been achieved by applying the unified theory of spiral scannings for nonvolumetric antennas and adopting either an oblate ellipsoid or a double bowl to shape an antenna with a quasi-planar geometry. By using these modelings, instead of the spherical one, it is possible to significantly reduce the error due to the truncation of the scanning zone, since the NF data can be acquired on a spiral lying on a plane located at a distance smaller than one half of the antenna maximum size. The NF data required by the standard plane-rectangular NF–FF transformation are then accurately recovered from those collected along the spiral. Some experimental results, obtained at the Antenna Characterization Lab of the University of Salerno and assessing the effectiveness of the techniques, are shown.

Near-Field to Far-Field Transformation Techniques with Spiral Scannings: A Comprehensive Review

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.

Application of Nonredundant Sampling Representations of Electromagnetic Fields to NF-FF Transformation Techniques

An overview of the application of the band-limitation properties and nonredundant sampling representations of electromagnetic fields to NF-FF transformations is presented. The progresses achieved by applying them to data acquired on conventional NF scanning surfaces are discussed, outlining the remarkable reduction in the number of needed NF samples and measurement time. An optimal sampling interpolation expansion for reconstructing the probe response on a rotational scanning surface from a non-redundant number of its samples is also discussed. A unified theory of the NF-FF transformations with spiral scannings, which allow a remarkable reduction of the measurement time, is then reviewed by describing a sampling representation of the voltage on a quite arbitrary rotational surface from its nonredundant samples collected on a proper spiral wrapping it. Some numerical and experimental results assessing the effectiveness of the considered NF-FF transformations are shown too.

A Nonredundant Near-Field to Far-Field Transformation with Spherical Spiral Scanning for Nonspherical Antennas

A Nonredundant Near-Field to Far-Field Transformation with Spherical Spiral Scanning for Nonspherical Antennas

THE UNIFIED THEORY OF NEAR-FIELD-FAR-FIELD TRANSFORMATIONS WITH SPIRAL SCANNINGS FOR NONSPHERICAL ANTENNAS

The unified theory of near-field–far-field transformations with spiral scannings for quasi-spherical antennas is extended in this paper to the case of nonspherical ones, i.e., antennas with two dimensions very different from the third one. To this end, these antennas are no longer considered as enclosed in a sphere, but in a proper convex domain bounded by a rotational surface. The extension, heuristically derived by paralleling the rigorous procedure valid for the spherical source modelling, allows one to overcome its main and serious drawbacks. In fact, the corresponding near-field–farfield transformations use a reduced number of near-field measurements and, above all, allow one to consider measurement surfaces at a distance smaller than one half the antenna maximum size, thus remarkably reducing the error related to the truncation of the scanning zone. These are very important features, which make the spiral scannings more and more appealing from the practical viewpoint. Some examples of the application of this theory to spirals wrapping the conventional scanning surfaces employed in the near-field–far-field transformations are reported, and the accuracy and robustness of the far-field reconstructions are assessed.

THEORETICAL FOUNDATIONS OF NEAR-FIELD-FAR-FIELD TRANSFORMATIONS WITH SPIRAL SCANNINGS

In this paper, the theoretical foundations of near-field-farfield transformations with spiral scannings are revisited and a unified theory is provided. This is accomplished by introducing a sampling representation of the radiated electromagnetic field on a rotational surface from the knowledge of a nonredundant number of its samples on a spiral wrapping the surface. The obtained results are general, since they are valid for spirals wrapping on quite arbitrary rotational surfaces, and can be directly applied to the pattern reconstruction via near-field-far-field transformation techniques. Numerical tests are reported for demonstrating the accuracy of the approach and its stability with respect to random errors affecting the data.