Abstract
This research falls in the antenna measurements related topic, and deals with the problem occurring in the classical spherical near-to-far-field (NTFF) transformation, when it becomes unpractical to mount the antenna under test (AUT) with its center at the center of the scanning sphere. This issue reflects in a growth of the number of near-field (NF) samples to be acquired, since this number depends on the radius of the minimum sphere, which contains the antenna, and is centered at the scanning sphere center. The non-redundant sampling representations of the electromagnetic field are conveniently exploited, to develop an effective spherical NTFF transformation for non-centered AUTs with quasi-planar geometry, requiring a minimum amount of NF samples, and nearly the same as that for a centered mounting of the AUT. Then, the NF data needed to perform the classical NTFF transformation are determined in efficient way from the acquired non-redundant NF samples by employing an accurate 2-D sampling interpolation scheme. Thus, it is possible to significantly save measurement time. Some simulation and laboratory results are reported to show the effectiveness of the developed technique, which takes into account a non-centered AUT mounting.
Highlights
In any way antenna measurements are accomplished, either through far-field (FF) test ranges, or near-field (NF) facilities, or compact range systems, they represent a useful tool to assess and improve the performance of the antennas involved in radio links, as well as in radar systems
This occurrence reflects in a growth of the amount of the NF data needed by the classical NTFF transformation technique [14], since, according to the minimum sphere rule, the radius of the smallest ball enclosing the antenna with its center at the scanning sphere one increases
The antenna under test (AUT) considered in the simulations is a uniform circular array having diameter 2a = 30λ, lying on the plane z = ds = 9λ, simulating its offset mounting in a spherical NF facility
Summary
In any way antenna measurements are accomplished, either through far-field (FF) test ranges, or near-field (NF) facilities, or compact range systems, they represent a useful tool to assess and improve the performance of the antennas involved in radio links, as well as in radar systems. There may be practical issues, such as particular arrangements of the antenna on its supports, mechanical constraints of the involved NF set-up, or its special arrangement, preventing the possibility of a centered mounting, that is to say, a mounting where the AUT geometric center coincides with the center of the measurement sphere This occurrence reflects in a growth of the amount of the NF data needed by the classical NTFF transformation technique [14], since, according to the minimum sphere rule, the radius of the smallest ball enclosing the antenna with its center at the scanning sphere one increases. Amount of NF samples as a minimum, and are nearly coincident in both cases of centered and non-centered mountings, making toRget a 1'remarkable saving of measurement time To this end, a non-redundant voltage representation is properly developed by adopting a two-bowls, which to model in a flexible and effective actual quasi-planar antennas.
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