A Large Spherical Near-Field Arch Scanner for Characterizing Low-Frequency Phased Arrays

Author: Scott McBride, Jeffrey P. Marier, Charles J. Kryzak, Jeffrey Fordham, Kefeng Liu

An arch-based spherical near-field measurement system has been commissioned at Lockheed Martin’s facility in Syracuse, New York. This system is designed for highfidelity testing of large, low-frequency, phased-array radars. The near-field scanner system consists of a 9.5- meter-radius arch with an active probe-position-error correction, and a large azimuth axis capable of carrying large arrays. The shielded anechoic chamber designed to house the measurement system includes full treatment with curvilinear absorber to achieve low levels of stray signal at UHF band frequencies, FM-200 / VESDA fire protection, and a glycol based system for removing heat loads generated by the radars.

The overall measurement system details are presented, along with mechanical accuracies achieved for the scanner system. Details of the chamber and host facility are described. Finally, the paper concludes with measurements of a UHF-band Standard Gain Horn using the system. The challenges and benefits of such a system will be highlighted.

A Theoretical Description of the IsoFilterTM Rejection Curve

Author: Doren W. Hess

In a 2008 AMTA paper the concept of the IsoFilterTM rejection curve was described. The steps to generate this rejection curve consist simply of (1) translating the coordinate origin of the measured pattern to a new location (2) performing a spherical modal analysis of the pattern, and (3) taking the total power in the lowest order mode as a measure of the strength of the radiation source at that location. Stepwise repetition of this process then generates the IsoFilterTM rejection curve. The basis for the process of generation was an empirical recipe for which no theoretical basis was presented. In this paper we relate the rejection curve to conventional electromagnetic theory. We begin with the general free space Green's function assuming a general distribution of current sources, and show how one may plausibly describe the IsoFilterTM rejection curve, and how it operates to reveal an arbitrary source distribution.

Advances in Cylindrical Mathematical Absorber Reflection Suppression

Authors: S.F. Gregson, A.C. Newell, G.E. Hindman, M.J. Carey

In many instances, reflections within antenna test ranges constitute the largest single component within the facilitylevel error budget. For some time, a frequency domain measurement and post-processing technique named Mathematical Absorber Reflection Suppression (MARS) has been successfully used to reduce range multi-path effects within spherical near-field and far-field antenna measurement systems. More recently, a related technique has been developed for use with cylindrical near-field antenna measurement systems. This paper provides an introduction to the measurement technique and novel probe pattern corrected near-field to farfield transform algorithm. It then presents the most recent results of an ongoing validation campaign detailing a number of the most recent advances which are found to yield improvements comparable to those attained with the corresponding spherical MARS technique. The results are discussed and conclusions presented.

You have requested a Reprint of an IET Paper

Copyright 2010 IET. Reprinted from The Fourth European Conference on Antennas and Propagation (EuCAP 2010) 12-16 April 2010.

This material is posted here with permission of The Institution of Engineering and Technology (IET). Such permission of the IET does not in any way imply IET endorsement of any of NSI-MI Technologies' products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IET.

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Alignment Sensitivity and Correction Methods for Millimeter Wave Spherical Near-Field Measurements

Authors: Greg Hindman, Allen Newell, Luciano Dicecca, Jean Christophe Angevain

Millimeter-wave measurements on spherical nearfield scanning systems present a number of technical challenges to be overcome to guarantee accurate measurements are achieved. This paper will focus on the affect of mechanical alignment errors of the spherical rotator system on the antenna’s measured performance. Methods of precision alignment will be reviewed. Sensitivity to induced mechanical alignment errors and their affect on various antenna parameters will be shown and discussed. Correction methods for residual alignment errors will also be described. The study includes 38 and 48 GHz data on the Alphasat EM model offset reflector antenna measured by TeS in Tito, Italy on a NSI-700S-60 Spherical Nearfield system, as well as a 40 GHz waveguide array antenna measured by NSI on a similar NSI-700S-60 Spherical Nearfield System at its factory in Torrance, CA, USA.

Antenna Phase Center Effects and Measurements in GNSS Ranging Applications

Author: Waldemar Kunysz

Antenna phase center offset (PCO) location and phase center variation (PCV) play an important role in high-precision GNSS ranging applications that use carrier-phase measurements. For ranging systems that use CDMA code-phase measurements, other statistics play a similar role – antenna group delay center offset (GDCO) and group delay variation (GDV). This paper describes the methods of how to measure and compute these statistics based on amplitude and phase pattern measured for a given antenna. A susceptibility analysis of these statistics versus multipath and antenna design parameters is also made. Practical examples on how to deal with undesired movement of PCO or larger variation of PCV is presented as well.

You have requested a Reprint of an IEEE Paper

Copyright 2010 IEEE. Reprinted from 2010 Antenna Measurement Conference, ANTEM 2010, July 5-9, 2010, Ottawa, Canada.

This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of NSI-MI Technologies' products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org.

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Applicability of IsoFilterTM Selectivity to Antenna Diagnostics

Authors:Doren W. Hess, Scott McBride

We have devised a method for identifying the locations and strengths of an antenna's radiation sources that is an alternative to conventional back-projection. This alternative method utilizes the antenna's measured far-field radiation pattern and successive spherical modal analyses to ascertain the relative strength of the antenna's sources, as a function of position, that give rise to the far-field.

Back-Projection to the Aperture of a Planar Phased Array from Data Obtained with a Spherical Near-Field Arch

Authors: Doren W. Hess, Scott McBride

We describe two theoretical bases for an algorithm for back-projection. The first is (1) Fourier inversion of the mathematical expression for the far electric field components in terms of the aperture electric field. The second is (2) Fourier inversion of the complete vectorial transmitting characteristic of Kerns' scattering matrix. It is this characteristic that results from the standard process of planar near-field (PNF) scanning and the ensuing reduction of the PNF transmission equation. We demonstrate that the theoretical approaches (1) and (2) yield identical back-projection algorithms. We report on backprojection measurements of an 18 inch X-band flat plate phased array using the far-field obtained from spherical near-field scanning. The spherical measurements were made on a large arch range.

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