Abstract
An efficient near-to-far-field transformation (NTFFT) technique, wherein the near-field (NF) measurements are acquired along a planar spiral with a uniform step to make the control of the involved positioners easier, is developed in this article. Such a technique is tailored for quasi-spherical, i.e., volumetric, antennas under test and makes use of a reduced number of NF data. An effective two-dimensional sampling interpolation algorithm, allowing the accurate reconstruction of the input NF data for the standard NTFFT with plane-rectangular scan, is obtained by setting the spiral step equal to the sample spacing required for interpolating along a radial line according to the spatial bandlimitation properties of electromagnetic fields, and by properly developing a non-redundant representation along such a spiral. Tests results are reported to demonstrate that the proposed NTFFT technique retains the same accuracy as the standard plane-rectangular one.
Highlights
The accurate characterization of an antenna is a metrological challenge whose complexity depends on the region surrounding the antenna under test (AUT), wherein the data are measured, i.e., the near-field (NF) or far-field (FF) region, the measurement environment, the facility used to collect the measurements, and the characteristics to be determined [1,2]
Drawbacks related to the transportation and mounting of these AUTs make these kinds of measurements unpractical and, due to the weather conditions and the presence of electromagnetic (EM) interferences, inaccurate
The complexity grows in such a case, the NF measurements allow us to obtain the complete FF pattern of the AUT, and to exploit the available information for diagnostic purposes
Summary
The accurate characterization of an antenna is a metrological challenge whose complexity depends on the region surrounding the antenna under test (AUT), wherein the data are measured, i.e., the near-field (NF) or far-field (FF) region, the measurement environment, the facility used to collect the measurements, and the characteristics to be determined [1,2]. The remarkable saving of measurement time is due to both the hugely reduced number of required NF samples and to how the rotary movement of the AUT positioner and the linear one of the probe positioner are combined during the acquisition on fly In any case, such a drastic measurement time saving is obtained at the expense of a non-uniform step of the spiral [28,29,30,31]. This article’s aim is to develop an effective NTFFT technique with planar spiral scanning for volumetric AUTs, wherein the spiral step is uniform and, the velocity of the linear positioner is constant To this end, by paralleling the reasoning made in [34].
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