2012 Technical Papers

Achieved Accuracy of a Spherical Near-Field Arch Positioning System

Authors: Jeffrey Fordham, Tim Schwartz, George Cawthon, Youlian Netzov, Scott McBride, Makary Awadalla, Dave Wayne

Publication: EuCAP 2012

Copyright Owner: IEEE

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.

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.

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Adaptive Acquisition Techniques for Planar Near-Field Antenna Measurements - Part 2

Authors: Daniël Janse van Rensburg

Publication: AMTA 2012

Copyright Owner: NSI-MI Technologies

The use of adaptive acquisition techniques to reduce the overall test time in planar near-field antenna measurements was presented in [1] & [2]. In those publications the concept of a decision function to track the uncertainty of a measurement as the data acquisition proceeds and also to adapt the acquisition region dynamically, was introduced. In this publication we build upon that work and present the concept of near-field array initialization. This is tested on different antennas and simulation results are presented. We also present actual measurement results to validate simulations that have to date been used to demonstrate advantages of the adaptive techniques.

Advances in Antenna Measurement Instrumentation and Systems

Authors: Steven R. Nichols, Roger Dygert, David Wayne

Publication: EuCAP 2012

Copyright Owner: IEEE

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 providing higher productivity, more efficient use of test facilities, and reduced data acquisition time.

Recently, measurement speeds of microwave receivers and vector network analyzers have advanced considerably. To take full advantage of these speed improvements, the measurement system architecture must be carefully considered. A comparison of several system architectures is given, along with discussion of key concepts and parameters that affect system timing, and a general method of calculating overall test time.

A summary table illustrates that small timing differences due to instrumentation and system architecture can have a significant impact on overall test time.

Further advances in system throughput are being explored using techniques such as simultaneous multi-frequency measurements in conjunction with a narrowband or wide band Receiver. A brief description of these techniques and initial proof of concept results are included.

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Computational and Experimental Verification of Far-Field Mathematical Absorber Reflection Suppression

Authors: S.F. Gregson, J. McCormick, B.J. Kerse, A.C. Newell, G.E. Hindman

Publication: EuCAP 2012

Copyright Owner: IEEE

The Mathematical Absorber Reflection Suppression (MARS) technique which is used to identify and supress effects of spurious scattering within antenna measurement systems is demonstrated and its effectiveness examined through computational electromagnetic simulation and actual range measurements which were taken using a dual cylindrical reflector compact antenna test range.

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Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction

Authors: Allen Newell, Stuart Gregson

Publication: AMTA 2012

Copyright Owner: NSI-MI Technologies

The numerical analysis used for efficient processing of spherical near-field data requires that the far-field pattern of the probe can be expressed using only azimuthal modes with indices of μ = ±1. (1) If the probe satisfies this symmetry requirement, near-field data is only required for the two angles of probe rotation about its axis of χ = 0 and 90 degrees and numerical integration in χ is not required. This reduces both measurement and computation time and so it is desirable to use probes that will satisfy the μ = ±1 criteria. Circularly symmetric probes can be constructed that reduce the higher order modes to very low levels and for probes like open ended rectangular waveguides (OEWG) the effect of the higher order modes can be reduced by using a measurement radius that reduces the subtended angle of the AUT. Some analysis and simulation have been done to estimate the effect of using a probe with the higher order modes (2) – (6) and the following study is another effort to develop guidelines for the properties of the probe and the measurement radius that will reduce the effect of higher order modes to minimal levels. This study is based on the observation that since the higher order probe azimuthal modes are directly related to the probe properties for rotation about its axis, the near-field data that should be most sensitive to these modes is a near-field polarization measurement. This measurement is taken with the probe at a fixed (x,y,z) or (θ,φ,r) position and the probe is rotated about its axis by the angle

Examination of Far-FieldMathematical Absorber Reflection Suppression through Computational Electromagnetic Simulation

Authors: S. F. Gregson, A. C. Newell, and G. E. Hindman

Publication: International Journal of Antennas & Propagation

Copyright Owner: IEEE

The mathematical absorber reflection suppression (MARS) technique has been used to identify and then suppress the effects of spurious scattering within spherical, cylindrical, and planar near-field antenna measurement systems, compact antenna test ranges (CATRs), and far-field measurement facilities for some time now. The recent development of a general-purpose threedimensional computational electromagnetic model of a spherical antenna test system has enabled the MARS measurement and postprocessing technique to be further investigated. This paper provides an overview of the far-field MARS technique and presents an introduction to the computational electromagnetic range model. Preliminary results of computational electromagnetic range simulations that replicate typical MARS measurement configurations are presented and discussed which, for the first time, confirm through simulation many of the observations that have previously been noted using purely empirical techniques.

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