Ovidio Mario Bucci

Data reduction in the NF-FF transformation technique with spherical scanning

A fast, accurate and stable two-dimensional sampling interpolation algorithm is developed to reconstruct the electromagnetic field radiated on a sphere in the antenna near-field region. Its analytical foundation relies on the recent theoretical results concerning the nonredundant field representations on curves and surfaces. The use of an ellipsoid (prolate or oblate) as modelling of the source allows one to reduce the number of required samples with respect to the spherical source modelling that, although more general, becomes redundant when considering antennas having one or two predominant dimensions. The obtained results are properly used to get ready an effective near-field-far-field transformation technique with spherical scanning, which requires a minimum number of data, thus reducing significantly the memory storage requirements and measurement time. Numerical examples assess the efficiency and the stability of the reconstruction process.

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.

Nonredundant Nf-Ff Transformation With Helicoidal Scanning

A probe compensated near-field-far-field (NF-FF) transformation technique with helicoidal scanning, which makes use of a minimum number of probe output voltage samples, is developed in this paper. This target is achieved by using a nonuniform helix as scanning curve, i.e., a circular helix with a constant angular elevation step, and by developing an efficient sampling representation over it. Then, by choosing the step coincident with the spacing needed to interpolate the probe voltage along a generatrix, it is possible to reconstruct such a voltage at any point over the cylinder. This allows the recovering of the data required by the standard probe compensated NF-FF transformation technique with cylindrical scanning. As compared with the previous technique employing a uniform helix with a constant linear elevation step, it allows one to reduce remarkably the number of needed samples without affecting the numerical efficiency. Numerical examples assess the accuracy and the stability of the FF reconstruction process.

A new near-field sampling representation from samples on planar spirals

A new convenient scanning geometry, the bi-polar one, has been introduced which allows simpler mechanical movements of the positioning system, thus enhancing its reliability and reducing its cost. In order to further reduce the complexity of the measurement set up as well as the time required for data acquisition, a continuous movement of the positioning system has been suggested leading to measurement points lying on a planar spiral. An effective exploitation of this new scanning system demand for a non-redundant field representation over a spiral (in order to get the minimum number of measurements required and the corresponding samples positions) allowing an efficient interpolation scheme for the evaluation of the field over the scanning plane, typically on a regular rectangular grid of /spl lambda//2 spaced points. In the past a large amount of effort has been devoted in the determination of a non-redundant and numerically efficient representation of the fields on canonical scanning surfaces in order to state the minimum number of required samples, their locations and to develop efficient interpolation algorithms. New field interpolation series allowing the use of a finite number of samples either on a bounded as well as unbounded observation line have been introduced at the University of Naples. Taking into account these results, a new interpolation series of the near-field on a planar spiral is introduced. Furthermore, an interpolation scheme is applied which allows one to evaluate the field on all the measurement planes from samples on a spiral line.