2007 Technical Papers

An Algorithm for Automated Phase Center Determination and its Implementation

Author: Pieter N. Betjes

Publication: AMTA 2007

Copyright Owner: NSI-MI Technologies

An efficient algorithm for calculating the position of the phase center of an antenna from a measurement is derived and implemented in software. Application of the algorithm to actual measurements shows that the success of the algorithm depends on characteristics of the antenna and a weighing parameter derived from the amplitude pattern.

An Investigation of Adaptive Acquisition Techniques for Planar Near-Field Antenna Measurement

Authors: G. Parsons, D.A. McNamara, D.J. Janse van Rensburg

Publication: IEEE AP-S Symposium 2007

Copyright Owner: IEEE

Reduce Near-Field Data Acquisition Time > Using an Existing Conventional PNF Facility & Operation > Data Acquisition Time (Physical Movement of the Probe) > Work Represents Our Moving in the Direction of Building Feedback/Adaptivity into Near-Field Measurements Dominates Testing Time

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Design, Alignment, and Calibration Requirements for a Sub-Millimeter Wave Frequency Tiltable Lightweight Scanner

Author: Peter W. Bond, P.E., G. A. Ediss

Publication: AMTA 2007

Copyright Owner: NSI-MI Technologies

This paper discusses design aspects related to a tiltable lightweight near-field scanning system for use at submillimeter frequencies. It addresses design issues as they relate to accuracy and scanner distortions from multiple causes. Calibration methods to measure and correct for anticipated and unanticipated errors are briefly addressed. Actual test results are presented.

The tiltable scanner being discussed was designed for the Atacama Large Millimeter/submillimeter Array (ALMA) [1] and is being used by the National Radio Astronomy Observatory (NRAO) [2]. It has many other applications by virtue of its light weight (approx. 120 lbs) and ability to be oriented at different angles. These include flightline testing and other in-situ antenna test applications.

EHF Rotman Lens Fed Linear Array Multibeam Planar Near-Field Range Measurements

Authors: Mike Maybell, John Demas

Publication: AMTA 2007

Copyright Owner: NSI-MI Technologies

Realized gain measurements of a 44 beam 44 element linear array over a 43.5 to 45.5 GHz design frequency range are presented. The prototype array1 is designed as a single column of a 50 column multibeam 2200 element planar active receive array for geostationary satellite communications payload. The 2200 element planar array is designed to form 1760 simultaneous narrow 0.4 degree beams, 1463 of which intercept the earth. The multibeam single prototype column realized gain was tested at the Nearfield Systems Inc.'s (NSI) facility using a 12’ x 12’ Planar Near-Field Range. Two different linear array configurations were tested. Each configuration utilized the same WR-19 waveguide fed 44 beam, 44 element Rotman lens and integrated RF distribution network (RFD). An active receive array utilizing only the center 8 array elements of the Rotman lens feed was tested first. This was followed by a 44 array element passive array test demonstrating the narrow 0.4 degree half power beamwidth. Summary and specific examples of the NFR test results will be presented. These will be compared with that predicted using the previously measured lens array factor gain (AFG) and embedded element realized gain. The AFG was measured using a HP8510C automatic network analyzer.

Fast and Accurate Antenna Alignment Correction Performed Using a Vector Isometric Rotation

Authors: Stuart F. Gregson, Clive G. Parini, John McCormick

Publication: Loughborough Antennas and Propagation Confererence (LAPC)

Copyright Owner: IEEE

The success of most traditional implementations of antenna measurement techniques whether near field, far field or compact, assume that a fiducial mechanical datum associated with the antenna under test (AUT) can be accurately and precisely aligned to the mechanical axes of the test range. Unfortunately, an alternative approach is sometimes necessary, as achieving such careful alignment is not always convenient or possible. Instead, if the relationship between the frame of reference associated with the antenna and the frame of reference associate with the range can be acquired, i.e. assuming that it is known, then in principal any misalignment can be corrected for within the data processing chain. Techniques for rigorously implementing the necessary vector isometric rotation are well documented and usually utilise the concepts of a modal expansion. In general this is not always convenient as these methods can be difficult to implement and often require the transformation of one modal expansion to another, e.g. planar or cylindrical to spherical, etc.. This paper describes the additional post processing that is required to yield alignment corrected far field data from an acquisition of an imperfectly aligned antenna. A general-purpose vector isometric rotation strategy is utilised that is reliant upon interpolation, rather than a particular modal expansion. The interpolation is performed using a polar, i.e. amplitude and phase, implementation of a two dimensional bi-cubic convolution interpolation algorithm. The effectiveness of this technique is then demonstrated through the use of range measurements.

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Histogram Equalisation as a Method for Making an Objective Comparison Between Antenna Patterns Functions

Authors: S.F. Gregson, J. McCormick, C.G. Parini

Publication: EuCAP 2007

Copyright Owner: IEEE

Attempts to produce robust, objective, quantitative measures of comparison between data sets using statistical methods have been widely reported in the literature. Recently, techniques have been developed that require the antenna pattern functions to be converted into histograms before the comparison, i.e. the measure of adjacency, is made.

The success of such a tactic can be crucially dependent upon the choice of categorising “bins”. As the number, level, and size of these bins can be chosen both a priori and freely, it is possible that the resulting histograms will be sparsely populated with the majority of the samples falling within only a few of the categories. This difficulty can be avoided if the bins are defined in such a way that roughly equal numbers of samples fall within each of the categorising bin.

This paper describes an efficient method for “equalising” any histogram and illustrates the effectiveness of this strategy with example, measured data.

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