An Experimental Validation of the Near-Field - Far-Field Transformation with Spherical Spiral Scan

Authors: F. D’Agostino, F. Ferrara, J.A. Fordham, C. Gennarelli, R. Guerriero, M. Migliozzi
Publication: AMTA 2012
Copyright Owner: University of Salerno

This work concerns the experimental validation of a probe compensated near-field – far-field transformation technique using a spherical spiral scanning, which allows one to significantly reduce the measurement time by means of continuous and synchronized movements of the positioning systems of the probe and antenna under test. Such a technique relies on the nonredundant sampling representations of the electromagnetic fields and makes use of a two-dimensional optimal sampling interpolation formula to recover the near-field data needed to perform the classical spherical near-field – far-field transformation. The good agreement between the so reconstructed far-field patterns and those obtained via the classical spherical near-field – far-field transformation assesses the effectiveness of the approach.

You have requested a Reprint of a University of Salerno Paper

Copyright 2012 The University of Salerno. Reprinted from AMTA 2012 Conference

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An Innovative Technique for Positioner Error Correction

Authors: Roger Dygert, Mark Hudgens, Steven R. Nichols
Publication: AMTA 2012
Copyright Owner: NSI-MI Technologies

Antenna measurement systems employ mechanical positioners to spatially orient antennas, vehicles, and a variety of other test articles. These mechanical devices exhibit native positioning accuracy in varying degrees based on their design and position feedback technology. Even the most precise positioning systems have insufficient native accuracy for some specific applications.

As the limits of economical positioning accuracy are approached, a new error correction technique developed by MI Technologies satisfies these higher accuracy requirements without resorting to extreme measures in positioner design. The new technique allows real-time correction of repeatable positioning errors. This is accomplished by (1) performing a finely grained measurement of positioner accuracy, (2) creating a map of the errors in both spatial and spatial frequency domains, (3) separating the errors into their various components, and (4) applying correction filters to algorithmically perform error correction within the positioner control system.

The technique may be used to achieve extreme positioning accuracy with positioners of high native accuracy. It may also be applied to conventional (synchro feedback) positioners to achieve impressive results with no modifications at all to the positioner. The following paper discusses the new error correction technique in detail.

An Interface Between a Near-Field Acquisition System and Active Arrays with Digital Beamformers

Authors: Scott T. McBride
Publication: AMTA 2012
Copyright Owner: NSI-MI Technologies

Phased-array antennas have always presented challenges in their interface to an acquisition system. Active arrays, especially those with a Digital Beam- Former (DBF), further complicate this interface. Whereas a passive phased array might be readily controlled with a simple digital code from the acquisition system, an active array tends to require more sophisticated communication to exercise the capabilities that must be tested. Furthermore, a DBF has receivers built into the array, and the simultaneous readings on these multiple receivers represent the data to be stored by the acquisition system vs. position and frequency.

The increased complexity of an active array's transmit beams by itself elevates the need for an interface between the array and the acquisition system. With the embedded receivers of a DBF, however, standard antenna testing of a DBF becomes nearly impossible without such an interface.

MI Technologies has developed a reasonably general interface between its acquisition system and active arrays with digital beamformers. MI has produced minor variations of this interface for multiple customers, and these customers will each use the interface to test multiple types of DBF active arrays. This paper discusses the challenges, capabilities, and architecture of this interface.

Exploration of the Feasibility of Adaptive Spherical Near-Field Antenna

Authors: Vincent Beaulé, Derek McNamara, Daniël Janse van Rensburg, Leili Shafai, Shantnu Mishra
Publication: AMTA 2012
Copyright Owner: NSI-MI Technologies

The feasibility of using adaptive acquisition techniques to reduce the overall testing time in spherical near-field (SNF) antenna measurements is investigated. The adaptive approach is based on the premise that near-field to far-field (NF-FF) transformation time is small compared to data acquisition time, so that such computations can be done repeatedly while data is being acquired. This allows us to use the transformed FF data to continuously compute and monitor pre-defined decision functions (formed from the antenna specifications most important to the particular AUT) while data is being acquired. We do not proceed with a complete scan of the measurement sphere but effectively allow the probe to follow a directed path under control of an acquisition rule, so that the sampled NF datapoints constitute an acquisition map on the sphere (the geographical allusion being purposeful). SNF data acquisition can be terminated based on decision function values, allowing the smallest amount of data needed to ensure accurate determination of the AUT performance measures. We demonstrate the approach using actual NF data for several decision functions and acquisition rules.

Antenna Diagnostics on Planar Arrays using a 3D Source Reconstruction Technique and Spherical Near-Field Measurements

Authors: Erik Jørgensen, Doren W. Hessy, Peter Meincke, Oscar Borries, Cecilia Cappellin, Jeff Fordhamy
Publication: EuCAP 2012
Copyright Owner: IEEE

In this paper, we apply a recently developed 3D source reconstruction algorithm to perform antenna diagnostics on a planar array configuration. The test case is a planar X-band slot array measured in a spherical near-field facility and two slots were intentionally covered during the measurement campaign to test the performance of the algorithm. These measured data have previously been analyzed in [1] using two different methods for planar back-projection. For the purpose of comparison, results obtained with a planar reconstruction method based on conversion of spherical waves are also presented.

You have requested a Reprint of an IEEE Paper

Copyright 2012 IEEE. Reprinted from EuCAP 2012 Conference.

This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of NSI-MI Technologies' products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org.

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Extending Cylindrical Mathematical Absorber Reflection Suppression To Further Reduce Range Scattering Errors

Authors: S.F. Gregson#, A.C. Newell, G.E. Hindman
Publication: The Loughborough Antennas and Propagation Conference 2012
Copyright Owner: IEEE

Recent work in developing a mode orthogonalisation and filtering post processing algorithm for multipath suppression in far-field and planar near-field antenna measurement systems has enabled worthwhile improvements to be obtained from the analogous, but mathematically and computationally distinct, cylindrical analogue. This paper presents an overview of the measurement and novel post-processing algorithm as embodied within the cylindrical mathematical absorber reflection suppression technique as well as comparing and contrasting results obtained from the new post-processing algorithms with previously published data.

You have requested a Reprint of an IEEE Paper

Copyright 2012 IEEE. Reprinted from The Loughborough Antennas and Propagation Conference, 2012.

This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of NSI-MI Technologies' products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org.

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Imaging of Element Excitations with Spherical Scanning

Authors: Doren W. Hess, Scott T. McBride
Publication: EuCAP 2012
Copyright Owner: IEEE

We review two conventional algorithms for aperture back-projection from spherical near-field data, with the goal of quantifying array-element excitations. The first algorithm produces that portion of the near field that radiates to the far field. The second algorithm divides out the element pattern prior to the transformation, and produces an estimate of the element excitations. We introduce a variation of this element-excitation algorithm that, for some arrays, can improve the fidelity of this conventional estimate. For the array geometries measured and simulated, this new algorithm shows dramatic improvement.

You have requested a Reprint of an IEEE Paper

Copyright 2012 IEEE. Reprinted from EuCAP 2012 Conference.

This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of NSI-MI Technologies' products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org.

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