Pattern Reconstruction of 3-D Modular Antennas by Means of a Non-Redundant Near-Field Spherical Scan

Abstract

A very flexible source model is proposed here to reduce the volumetric redundancy when considering the pattern reconstruction of three-dimensional modular antennas by means of a near-field spherical scan using a non-redundant sampling representation. Since this last facet is based on the appropriate choice of antenna model for the evaluation of the optimal parameters to be used, the proposed geometry guaranteed the minimum number of needed samples and then a significant time saved for data acquisition on the near-field spherical grid. Then, an optimal interpolation algorithm used these non-redundant samples for an accurate evaluation of the near-field data that were usable in the classical near-field to far-field transformation. The reliability and accuracy of the reconstruction process were proven by means of numerical tests. These last showed a remarkable reduction (about 53%) in needed near-field samples as compared to those required by the classical near-field to far-field transformation and this was achieved without any loss in accuracy.

An Effective Spherical NF/FF Transformation Suitable for Characterising an Antenna under Test in Presence of an Infinite Perfectly Conducting Ground Plane

“…The combined AUT of the equivalent problem can be considered a volumetric antenna, whose encumbrance has one or two predominant dimensions as compared to the other one(s), depending on the shape of the original antenna and its distance from the PEC ground. In order to choose the modelling surface Σ M able to best fit the real geometry of the combined AUT, whatever its encumbrance, the very adaptable surface proposed in [34] can be conveniently employed. Due to the geometry of the equivalent problem, the here adopted one bounds a central cylindrical body of radius a and height h c , which ends into two circular bowls with same aperture radii a and lateral bending radii c (see Figure 2b).…”

“…where ℓ ′ is the length of the curve C ′ , obtained by intersecting the meridian plane passing through Q with Σ M and equal to 2[h c + (a − c) + πc], and λ the wavelength. Then, the optimal parameter τ and phase function γ are [33,34]:…”

“…A very adaptable surface, bounding a central cylindrical body ended by two circular bowls with the same apertures and different bases, has been recently proposed [34] to characterise 3-D modular AUTs. As a matter of fact, it is able to best shape the geometry of such a kind of antenna, as well as any volumetric AUTs, by properly setting the height and the radius of the central body and the radii of the lateral bendings, thus minimising the volumetric redundancy, as well as the amount of the required measurements to be collected, as compared to a spherical modelling of the source.…”

“…The aim of this paper is to develop, according to the sampling strategy proposed in [38,39], a non-redundant NF/FF transformation with a hemispherical scan suitable for characterising volumetric AUTs whose encumbrance has one or two predominant dimensions as compared to the other one(s). Such a transformation technique makes use of the principle of image [37] to account for the PEC ground plane, which is supposed to be of infinite extent, and employs the adaptable surface developed in [34] to model the AUT and its image. It is possible to properly develop an efficient sampling representation over a sphere, wherein the sampling points lying on the upper hemisphere are the measurement points and the points belonging to the lower hemisphere are those at which the NF data have to be synthesised.…”

“…The paper is organised as follows: In Section 1, the interests and motivations for developing a non-redundant NF/FF transformation from NF data collected in the presence of a PEC ground plane and using very flexible antenna modelling to fit volumetric AUTs are stressed. In Section 2, an effective sampling representation of the voltage acquired by the probe over the scanning hemisphere is developed by properly applying the nonredundant representations of EM fields [33], by exploiting the principle of image [37] to account for the infinite PEC ground plane and by assuming the AUT and its image as contained in the adaptable surface developed in [34]. A two-dimensional OSI formula allowing one to accurately reconstruct the probe voltage at any point on the scanning sphere from a non-redundant number of its samples collected over the upper hemisphere is also developed in the same section.…”