Effective Antenna Modellings for NF-FF Transformations with Spherical Scanning Using the Minimum Number of Data

Abstract

Two efficient probe-compensated near-field-far-field transformations with spherical scanning for antennas having two dimensions very different from the third one are here developed. They rely on the nonredundant sampling representations of the electromagnetic fields and on the optimal sampling interpolation expansions, and use effective antenna modellings. In particular, an antenna with a predominant dimension is no longer considered as enclosed in a sphere but in a cylinder ended in two half spheres, whereas a surface formed by two circular “bowls” with the same aperture diameter but different lateral bends is adopted to shape an antenna with two predominant dimensions. These modellings are able to fit very well a lot of antennas by properly setting their geometric parameters. It is so possible to remarkably lower the number of data to be acquired, thus significantly reducing the measurement time. Numerical tests assessing the accuracy and the robustness of the techniques are reported.

Spherical Near-Field - Far-Field Transformation for Quasi-Planar Antennas from Irregularly Spaced Data

“…The key steps of the classical probe compensated NF -FF transformation with spherical scanning as modified in [14,15] are reported for reader's convenience. Let us consider a probe scanning a sphere of radius d in the antenna NF region, and adopt the spherical coordinate system   , , r   to denote an observation point …”

“…wherein the index of the highest spherical wave to be considered is rigorously fixed by the bandlimitation properties of the EM field and [13][14][15] is given by:…”

“…The orthogonality properties of the modes on such surfaces are then exploited to obtain the modal expansion coefficients, which allow the reconstruction of the AUT far field. Among the NF -FF transformation techniques, the one employing the spherical scanning has attracted remarkable attention since it allows the reconstruction of the complete radiation pattern of the AUT from a single set of NF measurements [7][8][9][10][11][12][13][14][15][16]. However, the computational effort is much greater than that required by planar and cylindrical NF facilities.…”

“…The ideal probe assumption, originally made in [13], has been removed in [14] so developing an effective probe compensated spherical NF -FF transformation technique for elongated or quasiplanar antennas. Finally, an efficient NF -FF transformation with spherical scanning, tailored to these kinds of antennas and based on different but very flexible AUT modellings, has been proposed in [15].…”

“…Section 2 briefly describes the classical probe compensated NF -FF transformation with spherical scanning as modified in [14,15]. Section 3 is devoted to the nonredundant sampling representation of the probe voltage over a sphere, based on an oblate ellipsoidal modelling of the AUT.…”