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550 Ghz Near-Field Antenna Measurement System for NASA Submillimeter Wave Astronomy Satellite

Author: Dan Slater

This paper describes a 550 GHz planar near-field measurement system developed for flight qualification of the radio telescope carried onboard the NASA submillimeter wave astronomy satellite (SWAS). The very high operating frequency required a new look at many near-field measurement issues. For example the short wavelength mandated a very high precision scanner mechanism with an accuracy of a few microns. A new thermal compensation technique was developed to minimize errors caused by thermally induced motion between the scanner and spacecraft antenna.

 

A Low Cost Spherical Near-Field System

Author: Jeff Way, Karl Haner

The Spherical Near-Field measurement technique has been in existence for a number of years. The cost associated with this type of measurement system has often been assumed to be substantial. Herein is presented the system configuration for a low cost Spherical Near-field System whose design goals include the capability for production line testing while retaining simplicity in approach. NSI has been contracted to provide a Spherical Near-field antenna measurement system. This paper focuses upon the design considerations undertaken during the prototype development of that system.

 

An Integrated Near-field EMC Measurement System

Author: Dan Slater

This paper briefly describes the theory and application of a small near-field imaging system designed for EMC precompliance applications. This system produces EMI and EMS images of circuit cards, cables and related items. If extended by using a phase coherent receiver in a region of free space propagation, this same system can precisely measure the radiation pattern of directive antennas and image the multipath within an anechoic chamber or TEM cell.

 

Anechoic Chamber Evaluation

Author: Karl Haner

This paper details the evaluation of a major aerospace company's tapered anechoic chamber. Using an NSI 3' x 3' near-field scanner and software, the chamber was evaluated at 11 frequencies and two polarizations. SAR imaging techniques were used to map the chamber reflections. A new addition to the software provided the ability to map the difference between the measured phase front and the theoretical spherical phase front; the software also derives the x, y, and z phase centers of the source. Error estimates for all aspects of the evaluation will be discussed.

 

Planar Near-field Measurements of Low-Sidelobe Antennas

Authors: Michael H. Francis and Allen C. Newell, Kenneth R. Grimm, John Hoffman, Helmut E. Schrank

The planar near-field measurement technique is a proven technology for measuring ordinary antennas operating in the microwave region. The development of very low-sidelobe antennas raises the question whether this technique can be used to accurately measure these antennas. We show that data taken with an open-end waveguide probe and processed with the planar near-field methodology, including probe correction, can be used to accurately measure the sidelobes of very low-side – 60 dB relative to the main beam peak. A special probe with a null in the direction of the main beam was also used for some of these measurements. This special probe reduced some of the measurement uncertainties but increased the uncertainties due to probe-antenna interactions. We discuss the major sources of uncertainty and show that the probe-antenna interaction is one of the limiting factors in making accurate measurements. The test antenna for this study was a slotted-waveguide array whose low sidelobes were known. The near-field measurement were conduced on the NIST planar near-field facility.

 

Position Correction on Large Near-Field Scanners Using an Optical Tracking System

Author: Greg Hindman

Large scanners used for near-field antenna measurements require careful attention to the design and fabrication process to maintain probe position accuracy1. This paper discusses the design, implementation, and results of a novel optical probe position tracking system used by NSI on a number of large near-field scanners. This system provides measurement of the probe X, Y and Z position errors, and real-time on-the-fly position correction. The use of this correction can significantly enhance measurement accuracy, and can reduce the cost of building large near-field scanners.

 

System Engineering for a Radome Test System

Author: John R. Jones, Virginia V. Jory, David R. Smith, Doren W. Hess, Jr., A. Reneé Soster, Alan L. Wilcox

This paper will discuss the system level design of a radome test system implemented in a compact range. The system includes a tracking pedestal controlled by an autotrack controller, a measurement receiver, a unique five-feed arrangement for the compact range which accommodates both tracking and measurement functions, and a laser autocollimator for coordinate system referencing. Key elements of system design include the required coordinate system transformations, the mechanical design of the positioning system and its contribution to the tracking system, and the synchronization of the autotrack controller, the measurement receiver, and the autotrack controller, the measurement receiver, and the system controller. There aspects of system design will be discussed and measurement and analysis results will be presented.

 
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