2010 Technical Papers

A Theoretical Description of the IsoFilter^TM Rejection Curve

Author: Doren W. Hess

Publication: AMTA 2010

Copyright Owner: NSI-MI Technologies

In a 2008 AMTA paper the concept of the IsoFilter^TM 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 IsoFilter^TM 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 IsoFilter^TM 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

Publication: EuCAP 2010

Copyright Owner: IEEE

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.

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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

Publication: AMTA 2010

Copyright Owner: NSI-MI Technologies

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

Publication: ANTEM 2010

Copyright Owner: IEEE

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.

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Applicability of IsoFilter^TM Selectivity to Antenna Diagnostics

Authors:Doren W. Hess, Scott McBride

Publication: EuCAP 2010

Copyright Owner: IEEE

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.

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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

Publication: EuCAP 2010

Copyright Owner: IEEE

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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