A Highly Accuracy Spherical Near-Field Arch Positioning System

Authors: Jeffrey Fordham, Tim Schwartz, George Cawthon, Youlian Netzov, Scott McBride, Makary Awadalla, Dave Wayne
Publication: AMTA 2011
Copyright Owner: NSI-MI Technologies

Highly accurate spherical near-field measurement systems require precise alignment of the probe antenna to the measurement surface. MI Technologies has designed and constructed a new spherical near field arch positioner with a 1.5 meter radius to support measurements requiring accurate knowledge of the probe phase center to within .0064 cm throughout its range of travel.

To achieve this level of accuracy, several key design elements were considered. First, a highly robust mechanical design was considered and implemented. Second, a tracking laser interferometer system was included in the system for characterization of residual errors in the position of the probe. Third, a position control system was implemented that would automatically correct for the residual errors.

The scanner includes a two position automated probe changer for automated measurements of multi-band antennas and a high accuracy azimuth axis. The azimuth axis includes an algorithm for correcting residual, repeatable positioning errors.

This paper defines the spherical near-field system and relation of each axis to the global coordinate system, discusses their associated error sources and the effect on global positioning and presents achieved highly accurate results.

A Theoretical Description of the IsoFilter Rejection Curve

Author: Doren W. Hess
Publication: EuCAP 2011
Copyright Owner: IEEE

The early work with the IsoFilterTM technique demonstrated that the radiation emanating from the aperture of a horn, located several wavelengths above a ground plane, could be separated from the radiation due to the sidelobe and backlobe illumination of the ground plane itself. The success of this demonstration encouraged us to pursue further the question of how well the IsoFilterTM technique worked to suppress other types of secondary signals – such as signals coming from other elements of an array antenna or another individual first-order primary radiator nearby. [1] In the process of evaluating the goodness of the secondary signal suppression we devised a method for identifying the locations and strengths of an antenna's radiation sources that is an alternative to conventional back-projection. The alternative method utilizes the antenna's far-field measured radiation pattern and successive spherical modal analyses to ascertain the relative strength of the antenna's sources that give rise to its far field. We believe that this alternative technique has applicability to the general problem of antenna diagnostics. Please see the Figure below for an example of an IsoFilterTM rejection curve. [2]

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Copyright 2011 IEEE. Reprinted from EuCAP 2011 Conference.

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Adaptive Acquisition Techniques for Planar Near-Field Antenna Measurements

Author: Daniël Janse van Rensburg
Publication: AMTA 2011
Copyright Owner: NSI-MI Technologies

The use of adaptive acquisition techniques to reduce the overall test time in planar near-field antenna measurements is described. A decision function is used to track the accuracy of a measurement as the data acquisition proceeds, and to halt such acquisition when this is considered sufficient for the measured quantity of importance. Possible decision functions are defined and compared. Several test cases are presented to show that significant test time reduction is possible when compared to traditional acquisition schemes.

Advanced Antenna Measurement System Architectures

Author: Steven R. Nichols
Publication: AMTA 2011
Copyright Owner: NSI-MI Technologies

Since the early days of antenna pattern recorders, advances in instrumentation and computers have enabled measurement systems to become highly automated and much more capable. Automated systems have provided higher productivity, more efficient use of test facilities, and the ability to acquire more data in less time. In recent years, measurement speeds of microwave receivers and vector network analyzers have advanced considerably. However, to take full advantage of these speed improvements, the measurement system architecture must be carefully considered. Small differences in instrument timing that are repeated many times can make large differences in system measurement time. This paper describes a general method of calculating system measurement time based on the primary factors that affect system timing, including position trigger detection, frequency switching time, multiplexer switching time, receiver measurement time, and timing overhead associated with triggers, sweeps, and measurements. It also shows how key features of instruments available today can be used along with improved antenna measurement system architectures to optimize system throughput.

Advances in Planar Mathematical Absorber Reflection Suppression

Authors: Stuart Gregson, Allen Newell, Greg Hindman
Publication: AMTA 2011
Copyright Owner: NSI-MI Technologies

When making antenna measurements, great care must be taken in order to obtain high quality data. This is especially true for near-field antenna measurements as a significant amount of mathematical post-processing is required in order that useful far-field data can be determined. However, it is often found that the integrity of these measurements can be compromised in a large part through range reflections, i.e. multipath [1]. For some time a technique named Mathematical Absorber Reflection Suppression (MARS) has been used to reduce range multi-path effects within spherical [2, 3], cylindrical [4, 5] and most recently planar [6, 7] nearfield antenna measurement systems. This paper presents the results of a recent test campaign which yields further verification of the effectiveness of the technique together with a reformulation of the post-processing algorithm which, for the first time, utilises a rigorous spherical wave expansion based orthogonalisation and filtering technique.

Antenna Pattern Comparison Using Pattern Subtraction and Statistical Analysis

Authors: A.C. Newell, G.E. Hindman
Publication: EuCAP 2011
Copyright Owner: IEEE

This paper discusses a technique that can be used when comparing two antenna patterns that produces a measure of the difference between the patterns and an associated confidence level for the results that is derived from a statistical analysis of the pattern differences. The first step in the process is to verify that the same coordinate system is used, and that the AUT is precisely aligned to those coordinates in all measurements. Small differences in beam pointing and polarization that correspond to rotations about the three rectangular axes can arise due to AUT alignment differences or due to some measurement errors. These changes in beam pointing can produce apparent pattern differences in the pattern comparison process that can distort the results, and adjustments in the AUT alignment or pattern data should be done before the pattern comparisons are carried out. It is easy to interpolate the pattern or change the pattern centering using standard processing software to try and correct for the angular misalignments, however the interpolation or centering may not completely correct for rotations about all three axes and some effects may remain after software adjustments...

You have requested a Reprint of an IEEE Paper

Copyright 2011 IEEE. Reprinted from EuCAP 2011 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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Application of Mathematical Absorber Reflection Suppression to Planar Near-Field Antenna Measurements

Authors: S.F. Gregson, A.C. Newell, G.E. Hindman, M.J. Carey
Publication: EuCAP 2011
Copyright Owner: IEEE

Nearly all antenna measurements are contaminated to some degree with fields scattered by objects within the environment of the test system. In many instances these reflections (i.e. multi-path) are found to constitute one of the most significant contributors to the facility-level error budget [1]. For some time, a frequency domain measurement and postprocessing technique named Mathematical Absorber Reflection Suppression (MARS) has been successfully used to reduce range multi-path effects within spherical [2, 3, 4] and cylindrical nearfield antenna measurement systems [5, 6]. More recently, a related technique has been developed for use with planar nearfield antenna measurement systems [7]. This paper provides an introduction to the measurement technique and novel probe pattern corrected near-field to far-field transform algorithm. It then presents the most recent results of an on-going validation campaign which have been found to yield improvements comparable to those attained with the corresponding spherical and cylindrical MARS implementations. These results are discussed and conclusions presented.

You have requested a Reprint of an IEEE Paper

Copyright 2011 IEEE. Reprinted from EuCAP 2011 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.

By choosing to view this document, you agree to all provisions of the copyright laws protecting it.


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