Far-Field Reconstruction From a Minimum Number of Spherical Spiral Data Using Effective Antenna Modelings

Abstract

Abstract-Two probe-compensated near-field-far-field transformations with spherical spiral scanning tailored for antennas having two of their dimensions very different from the third one are developed by properly applying the unified theory of spiral scans for nonspherical antennas. One is suitable for electrically long antennas, which are considered as enclosed in a cylinder ended in two half-spheres. The other adopts a surface formed by two circular "bowls" with the same aperture diameter but different lateral bends to shape a quasi-planar antenna. These flexible modelings fit very well many actual antennas by properly setting their geometric parameters. Great reduction of the number of data to be acquired is achieved, thus significantly reducing the required measurement time. Numerical tests validating the accuracy of the proposed techniques and their stability with respect to random errors affecting the data are shown.

Far-Field Reconstruction From Near-Field Data Acquired via a Fast Spherical Spiral Scan: Experimental Evidences

“…The NF-FF transformation with spherical spiral scan [28], using the two-bowls modelling ( Fig. 1) to shape quasi-planar antennas, is experimentally validated in this paper.…”

“…This suggestion has enabled the development of the innovative spiral scanning techniques [18][19][20][21][22][23][24][25][26][27][28][29]. Besides the use of continuous movements, the drastic time saving characterizing these scanning techniques is due to the significantly reduced number of needed NF data related to the application of the aforementioned nonredundant sampling representations, which can be further lowered if the surface Σ enclosing the AUT fits better its actual shape.…”

“…In particular, the nonredundant sampling representation on the sphere from samples collected along the spiral and the related OSI expansion have been developed in [23][24][25] by assuming the AUT as enclosed in the smallest sphere able to contain it and choosing the spiral step equal to the sample spacing required for the interpolation along a meridian. Then, NF-FF transformations with spherical spiral scanning tailored for electrically long or quasi-planar antennas have been proposed in [26][27][28] by properly applying the unified theory of spiral scans for nonspherical antennas [29]. In particular, a prolate [26] and an oblate [26,27] ellipsoid have been adopted to model an elongated and a quasi-planar antenna, respectively.…”

“…In particular, a prolate [26] and an oblate [26,27] ellipsoid have been adopted to model an elongated and a quasi-planar antenna, respectively. Whereas in [28], an elongated AUT has been considered as enclosed in a cylinder ended in two half spheres (rounded cylinder), and a surface formed by two circular bowls with the same aperture diameter but different bending radii (two-bowls modelling) has been used for modelling quasi-planar antennas. Generally, these last two flexible AUT modellings result to be more effective from the data reduction viewpoint than the corresponding ellipsoidal ones, since they are able to fit better the AUT shape by properly setting their geometric parameters.…”

“…Among the NF-FF transformations, that employing the spherical spiral scanning [23][24][25][26][27][28], as well as that employing the spherical one [12,13,16,[34][35][36], have attracted considerable attention, since they allow the full reconstruction of the AUT radiation pattern, even though the data processing is considerably more complex than that needed by planar and cylindrical NF facilities [1,2]. In particular, the nonredundant sampling representation on the sphere from samples collected along the spiral and the related OSI expansion have been developed in [23][24][25] by assuming the AUT as enclosed in the smallest sphere able to contain it and choosing the spiral step equal to the sample spacing required for the interpolation along a meridian.…”