A Dual-Ported Probe for Planar Near-Field Measurements

Authors: W. Keith Dishman, Doren W. Hess, and A. Renee Koster
Publication: AMTA 1992
Copyright Owner: NSI-MI Technologies

A dual-linearly polarized probe developed for use in planar near-field antenna measurements is described. This probe is based upon Scientific-Atlanta’s Series 31 Orthomode Feeds originally developed for spherical near-field testing. The unique features of this probe include dual-orthogonal linear ports, high polarization purity, excellent port-to-port isolation, an integrated coordinate system reference, APC-7 connectors, and a thin-wall horn aperture to minimize probe-AUT interactions. The probe was calibrated at the National Institute of Standards and Technology (NIST) and the calibration data consisting of the probe’s complete plane-wave spectrum receiving characteristic s'02(K) were imported directly into the Model 2095/PNF Microwave 02 Measurement System. This paper describes the dual-ported probe and its application in a planar near-field range.

 

An Implementation of the Three Cable Method

Author: O. M. Caldwell
Publication: AMTA 1992
Copyright Owner: NSI-MI Technologies

The three cable method for removing the amplitude and phase variations of microwave cables due to temperature change and movement can offer a substantial improvement in antenna measurement accuracy. Implementation details of the method are provided for a planar near-field range. Items specifically addressed are range configuration, hardware requirements, data collection methodology, identification and assessment of error sources, and data requirements.

 

Anechoic Chamber Diagnostic Imaging

Authors: Greg Hindman, Dan Slater
Publication: AMTA 1992
Copyright Owner: NSI-MI Technologies

Traditional techniques for evaluating the performance of anechoic chambers, compact ranges, and far-field ranges involve scanning a field probe through the quiet zone area. Plotting the amplitude and phase ripple yields a measure of the range performance which can be used in uncertainty estimates for future antenna tests. This technique, however, provides very little insight into the causes of the quiet-zone ripple. NSI's portable near-field scanners and diagnostic software can perform quiet-zone measurements which will provide angular image maps of the chamber reflections. This data can be used by engineers to actually improve the chamber performance by identifying and suppressing the sources of high reflections which cause quiet-zone ripple.

 

Design Considerations for a Planar Near-Field Scanner

Authors: Joseph H. Pape, James D. Huff, Alan L. Wilcox
Publication: AMTA 1992
Copyright Owner: NSI-MI Technologies

Planar Near-Field scanning is becoming the method of choice for the testing of many types of antennas. These antennas include planar phased arrays, space deployable satellite antennas and other antennas either too large to move during the test or otherwise sensitive to the gravity vector. The planar scanner is a major component of the measurement system and must provide an accurate and stable platform for moving the RF probe across the test antenna’s aperture. This paper describes basic design requirements for a planar near-field scanner. Based on recent development activity at Scientific-Atlanta several design considerations are presented. Scanner parameters discussed include basic scanner concepts and geometry, scanner accuracy and stability, RF system including cabling and accuracy, load carrying requirements of the RF probe carriage, position and readout systems and drive and control systems. A scanner will be presented which incorporates many of the design features discussed.

 

Evaluating Near-Field Range Multi-Path

Author: Gregory F. Masters
Publication: AMTA 1992
Copyright Owner: NSI-MI Technologies

Near-field range design includes the placement of RF absorber in the test area. Absorber placement depends highly on the antennas being tested. A common approach is to design an expensive low-reflection chamber around the near-field scanner. The chamber and the additional floor space can sometimes cost more than the near-field scanning system itself. Another approach seeks to identify multi-path reflection to minimize cost by optimally placing absorber to meet specific antenna test requirements. The result is a lower cost range using less floor space. This paper describes a technique of evaluating near-field range multipath.

 

Implementation of a Small Planar Near-Field System

Author: Christopher B. Brechin, Rebecca Kaffezakis
Publication: AMTA 1992
Copyright Owner: NSI-MI Technologies

This paper describes a novel planar near-field measurement system designed to test a beam-steered flat face phased array antenna. This system is unique in its ability to measure multiple beams during a single scan of the aperture. The system utilizes a very fast planar scanner with six foot by six foot of travel combined with fast beam-steering commands to significantly reduce the test time of multiple-beam phased array antennas. These features combined with software based on algorithms developed by the National Institute of Standards and Technology provide state of the art measurements of planar phased array antennas.

 

Principal of the Three-Cable Method for Compensation of Cable Variations

Author: Doren W. Hess
Publication: AMTA 1992
Copyright Owner: NSI-MI Technologies

A novel technique has been devised that permits a length of cable to be measured in place and its transfer characteristic monitored as motion occurs. The scheme is to measure the cable in transmission as a member of a pair and to infer the characteristic of the cable from a set of three pair-wise measurements, in analogy to the well-known three-antenna technique. From the resulting knowledge of the signal cable’s characteristic one can correct the measured data to account for the changes in the cable through which the signal of interest was passed.

 
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