Identifying Pointing Errors for the NIST 18 Term Error Technique

Author: Zachary Newbold, Bruce Williams, Allen Newell
Publication: AMTA 2009
Copyright Owner: NSI-MI Technologies

The NIST 18 Term Error Analysis Technique uses a combination of mathematical analysis, computer simulation and near-field measurements to estimate the uncertainty for near-field range results on a given antenna and frequency range. A subset of these error terms is considered for alignment accuracy of an antenna’s RF main beam. Of the 18 terms, several have no applicable influence on determining the beam pointing or the terms have a minor effect and when an RSS estimate is performed they are rendered inconsequential. The remainder become the dominant terms for identifying the alignment accuracy. There are six terms that can be evaluated to determine the main beam pointing uncertainty of an antenna with respect to dual band performance. Analysis of the near-field measurements is performed to identify the alignment uncertainty of the main beam with respect to a specified mechanical position as well as to the main beam of the second band.

Improving and Extending the MARS Technique to Reduce Scattering Errors

Author: Greg Hindman, Allen C. Newell
Publication: AMTA 2009
Copyright Owner: NSI-MI Technologies

The Mathematical Absorber Reflection Suppression (MARS) technique is a method to reduce scattering errors in near-field and far-field antenna measurement systems. Previous tests by the authors had indicated that NSI’s MARS technique was not as effective for directive antennas. A recent development of a scattering reduction technique for cylindrical near-field measurements has demonstrated that it can also work well for directive antennas. These measurements showed that the AUT should be offset from the origin by a distance at least equal to the largest dimension of the AUT rather than only 1-3 wavelengths which had been used for smaller antennas in the earlier MARS measurements. Spherical near-field measurements have recently been concluded which confirm that with the larger offsets, the MARS technique can be applied to directive antennas with excellent results...

Measuring Wide Angle Antenna Performance Using Small Cylindrical Scanners

Authors: S.F. Gregson, C.G. Parini, J. Dupuy
Publication: EuCAP 2009
Copyright Owner: IEEE

A near-field measurement technique for the prediction of wide-angle asymptotic far-field antenna patterns from data obtained from a modified small combination planar/cylindrical near-field measurement system is presented. This novel technique utilises a simple change in the alignment of the robotic positioners to enable near-field data to be taken over the surface of a conceptual right conic frustum. This configuration allows existing facilities to characterise wide-angle antenna performance in situations where hitherto they could have been limited by the effects of truncation. This paper aims to introduce the measurement technique, present a measurement campaign, describes the novel probe-corrected near-field to farfield transform algorithm before presenting preliminary results. As this paper recounts the progress of ongoing research, it concludes with a discussion of the remaining outstanding issues and presents an overview of the planned future work.

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Networked Acquisition Controller Reduces Antenna Test System Overhead

Authors: Derek Skousen, Marion Baggett
Publication: (MPD) Microwave Product Digest, March 2009 Issue
Copyright Owner: NSI-MI Technologies

Antenna characterization requires making large quantities of RF measurements across a known spatial position. In practice, this involves coordinated positioning equipment, test instruments, and software processing. The overhead of networking, handshaking, sequencing, triggering, and data management between these devices is often the limiting factor in total system performance. Antenna test engineers are often frustrated by slow system performance, despite using the fastest equipment available.

Numerical Calibration of Standard Gain Horns and OEWG Probes

Author: Donald G. Bodnar
Publication: AMTA 2009
Copyright Owner: NSI-MI Technologies

The gain-transfer technique is the most commonly used antenna gain measurement method and involves the comparison of the AUT gain to that of another antenna with known gain. At microwave frequencies and above, special pyramidal horn antennas known as standard-gain horns are universally accepted as the gain standard of choice. A design method and gain curves for these horns were developed by the US Naval Research Laboratory in 1954. This paper examines the ability of modern numerical electromagnetic modeling to predict the gain of these horns and possibly achieve greater accuracy than with the NRL approach.

Similar computational electromagnetic modeling is applied to predict the gain and pattern of open-ended waveguide probes which are used in near-field antenna measurements. This approach provides data for probes that are not available in the literature.

Portable RF Target Simulator

Authors: David Wayne, Andrew Schlegel, Steve Nichols, Don Bodnar, Doren Hess, George Cawthon, Anil Tellakula, Jeff Skinner, Trung Dam, Bill Myles, Harvey Gratt
Publication: AMTA 2009
Copyright Owner: NSI-MI Technologies

RF guided missile developers require flight simulation of their target engagements to develop their RF seeker. This usually involves the seeker mounted on a Flight Motion Simulator (FMS) as well as an RF target simulator that simulates the signature and motion of the target. Missile intercept engagements are unique in that they involve highly dynamic relative motion in a short period of time. This puts demanding requirements on the RF target simulator to adequately present the desired phase slope, amplitude, and polarization to the seeker antenna and electronics under test.

This paper describes a newly installed RF Target Simulator that addresses these requirements in a unique fashion. The design utilizes a compact range reflector, dynamically rotated in two axes as commanded by the flight simulation computer, to produce the desired changing phase slope and an RF feed network dynamically controlled to produce the desired changing polarization and amplitude. Physical optics analysis establishes an accurate correlation between reflector physical rotation and resulting angle-of-arrival of the wave front in the quiet zone. The RF Target Simulator is self contained in a two-man portable anechoic chamber that can be disengaged from the FMS and rolled to and from the FMS as needed. Measurements are presented showing the performance of the RF Target Simulator.

Radiation Pattern Measurement of the NASA Mars Science Laboratory UHF Entry Antenna Using a Spherical Near-Field Range

Authors: Paula R. Brown, David Farr, John Demas, Jesus A. Aguilar
Publication: AMTA 2009
Copyright Owner: NSI-MI Technologies

Measurements of a conical micro-strip WraparoundTM antenna array mounted on a portion of the entry vehicle for NASA’s Mars Science Laboratory mission were completed at Nearfield Systems, Inc.’s new spherical near-field range facility. The WraparoundTM antenna, designed and manufactured by Haigh-Farr, Inc., provides nearly full spherical coverage and operates in the UHF frequency band for telecommunications to orbiting assets at Mars. A summary of the measurements techniques and results are presented, along with a comparison of the measured and calculated patterns.

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