CATR Quiet Zone Modelling and the Prediction of “Measured” Radiation Pattern Errors: Comparison using a Variety of Electromagnetic Simulation Methods

Authors: C.G. Parini, R. Dubrovka, S.F. Gregson
Publication: AMTA 2015
Copyright Owner: NSI-MI Technologies

The successful design and implementation of a compact antenna test range (CATR) is predicated upon the availability of highly accurate and precise computational electromagnetic (CEM) modelling tools. As the accuracy of these models is paramount to both the design of the CATR and the subsequent determination of the facility level uncertainty budget, this paper presents an accuracy evaluation of five different CEM simulations. We report results using methods of CATR modelling including: geometrical-optics with geometrical theory of diffraction, plane-wave spectrum, Kirchhoff-Huygens and current element, before presenting results of their use in the farfield antenna pattern measurement prediction for given CATRAUT combinations.

Spherical Spiral Scanning for Automotive Antenna Measurements

Author: Jeffrey A. Fordham
Publication: AMTA 2015
Copyright Owners: NSI-MI Technologies, University of Salerno

Spherical spiral scanning involves coordinating the motion of two simultaneous axes to accomplish near-field antenna measurements along a line on a sphere that does not cross itself. The line would ideally start near a pole and trace a path along the sphere to the other pole. An RF probe is moved along this path in order to collect RF measurements at predefined locations. The data collected from these measurements is used along with a near-field to far-field transformation algorithm to determine the radiated far-field antenna pattern.

The method for transforming data collected along a spherical spiral scan has been previous presented [12, 13]. Later laboratory measurement studies have shown the validity of the technique

A review of the spherical spiral scanning technique and its recent advances, resulting from about ten years of research collaboration between the UNISA Antenna Characterization Research Group and MI Technologies is here presented. Such a scan technique relies on the non-redundant sampling representations of EM fields and takes full advantage of moving two axes simultaneously. Accordingly, it allows one to drastically reduce the overall number of required data and the time to collect the data. This scanning technique can be properly applied in testing antennas mounted on automobiles in order to reduce the overall time of the measurement.

Spherical Scanning Measurement Challenge for Future Millimeter Wave Applications

Authors: F. Ferrero, Y. Benoit, L. Brochier, J. Lanteri, J-Y Dauvignac, C. Migliaccio, S.F. Gregson
Publication: AMTA 2015
Copyright Owner: NSI-MI Technologies

A specific set-up for probe-fed antenna pattern measurements with an articulated arm has been developed with a 500mm AUT-probe distance. This paper will give an example of far-field measurement and highlight its advantages and limitations. A near-field approach to filter the probe effect is investigated. First measurement results, including amplitude and phase patterns, will be presented. Phase data will be leveraged to develop post-processing techniques to filter probe and environmental effects.

Spherical Geometry Selection Used for Error Evaluation

Authors: Greg Hindman, Pat Pelland, Greg Masters
Publication: AMTA 2015
Copyright Owner: NSI-MI Technologies

Spherical near-field error analysis is extremely useful in allowing engineers to attain high confidence in antenna measurement results. NSI has authored numerous papers on automated error analysis and spherical geometry choice related to near field measurement results. Prior work primarily relied on comparison of processed results from two different spherical geometries: Theta-Phi (0 ≤θ≤ 180, -180 ≤ φ ≤ 180) and Azimuth-Phi (-180 ≤θ≤ 180, 0 ≤ φ ≤ 180). Both datasets place the probe at appropriate points about the antenna to measure two different full spheres of data; however probe-to-antenna orientation differs in the two cases. In particular, geometry relative to chamber walls is different and can be used to provide insight into scattering and its reduction.

When a single measurement is made which allows both axes to rotate by 360 degrees both spheres are acquired in the same measurement (redundant). They can then be extracted separately in post-processing. In actual fact, once a redundant measurement is made, there are not just two different full spheres that can be extracted, but a continuum of different (though overlapping) spherical datasets that can be derived from the single measurement. For example, if the spherical sample density in Phi is 5 degrees, one can select 72 different full sphere datasets by shifting the start of the dataset in increments of 5 degrees and extracting the corresponding single-sphere subset. These spherical subsets can then be processed and compared to help evaluate system errors by observing the variation in gain, sidelobe, cross pol, etc. with the different subset selections.

This paper will show the usefulness of this technique along with a number of real world examples in spherical near field chambers. Inspection of the results can be instructive in some cases to allow selection of the appropriate spherical subset that gives the best antenna pattern accuracy while avoiding the corrupting influence of certain chamber artifacts like lights, doors, positioner supports, etc.

Structural Correction of a Spherical Near-Field Scanner for mm-Wave Applications

Authors: Daniël Janse van Rensburg & Pieter Betjes
Publication: AMTA 2015
Copyright Owner: NSI-MI Technologies

A spherical near-field test system allowing for the antenna under test to remain stationary during testing is described. The system is suitable for use at mm-wave ( > 50 GHz) frequencies. Fidelity of the structure for testing at these frequencies is critical and since the structure experiences a gravitational force as a function of probe position, a complex deformation map results. There is also a radial distance variation of the probe and a technique to correct for this variation (presented before) is expounded upon. We describe the structural perturbation observed on such a scanner and assess to what extent this limits high frequency application for spherical nearfield testing.

Utilizing Gain Interpolation for the Removal of Near-Field Coupling Effects during EMC Antenna Calibrations

Authors: Dennis Lewis, Vince Rodriguez, Sandra Fermiñan Rodríguez
Publication: EuCAP 2015
Copyright Owner: IEEE

Antenna calibrations for EMC emissions and immunity measurement require gain characterization at reduced distances. The current standards for EMC antenna calibrations do not address the near-field antenna-to–antenna interactions that are present during calibration at these reduced distances. These interactions are not present when using these antennas to measure a device and can result in large measurement errors. Extrapolation measurements have been used for many years to measure the far field gain of antennas at reduced distances. This paper uses both computations and measurements to show how the use of interpolation results in a more accurate assessment of antenna gain at distances required for EMC antenna calibrations.

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