2001 Technical Papers

A Large Aperture 650 GHz Near-Field Measurement System for the Earth Observing System Microwave Limb Sounder

Authors: Dan Slater, Paul Stek, Rick Cofield, Robert Dengler, Jack Hardy, Robert Jarnot, Ray Swindlehurst,

Publication: AMTA 2001

Copyright Owner: NSI-MI Technologies

This paper describes a large aperture, 650 GHz, planar near-field measurement system developed for field of view characterization of the Earth Observing System Microwave Limb Sounder (EOS MLS). Scheduled for launch in 2003 on the NASA EOS Aura spacecraft, EOS MLS is being developed by the Jet Propulsion Laboratory to study stratospheric chemistry using radiometers from 118 to 2500 GHz. The combination of a very high operating frequency and a 1.6-meter aperture, coupled with significant cost and weight restrictions, required a new look at near-field scanner design approaches. Nearfield Systems Inc. (NSI) developed a planar scanner that provides a planar accuracy of 4 microns RMS over the entire 2.4 x 2.4 meter scan area. This paper presents an overview of this system including the sub-millimeter wave RF subsystem and the ultrahigh precision scanner. Representative measurement results will be shown.

A Simple Analysis of Near-Field Boresight Error Requirements

Author: Doren W. Hess

Publication: AMTA 2001

Copyright Owner: NSI-MI Technologies

The need to measure the boresight pointing direction of radar antennas to a high degree of accuracy yields a requirement for excellent positioning accuracy on near-field antenna ranges. Evaluation of this requirement can be accomplished by a full and complete sensitivity analysis.

Alternatively, to gain an understanding of the effects of errors more simply, one can approach the question of accuracy required in the setup, by use of a physical model and straightforward physical reasoning. The approach starts with the assumptions of a collimated wave with planar phase fronts and the premise that the boresight direction of such a sum beam is along the normal to the phase fronts. A sensitivity analysis of the simple trigonometric boresight relationship between mechanical boresight and phase front normal, shows how accurate the receiver and the positioner must be to achieve a given boresight determination. Such an approach has been known for many years as it regards planar scanning; and, the results are known to be applicable.

In this paper this consideration is extended to spherical scanners to arrive at estimates of the mechanical positioner accuracies and electrical receiver accuracies needed to make boresight measurements of radar antennas with spherical near-field ranges.

Error Analysis of Circular-Polarization Components Synthesized from Linearly Polarized Measurements

Author: Pieter N. Betjes

Publication: AMTA 2001

Copyright Owner: NSI-MI Technologies

A usual way of performing pattern-measurements on circularly polarized antennas is by measuring the linear components of the field and mathematically converting those to the left-hand and right-hand circular components. These synthesized circular components are sensitive for a number of factors: The exact orthogonality of the measured linear components, the measurement-accuracy of both phase and amplitude of the measured linear components, the polarization-pureness (or the accuracy of the description of the polarization-characteristics) of the probe, etc. This paper analyzes these factors, using a computer-model. An indication on the requirements to be imposed on the measurement-equipment is provided.

Holographic Projection to an Arbitrary Plane from Spherical Near-Field Measurements

Authors: Allen C. Newell, Bert Schlüper, Robert J. Davis

Publication: AMTA 2001

Copyright Owner: NSI-MI Technologies

Holographic back-projections of planar near-field measurements to a plane have been available for some time. It is also straightforward to produce a hologram from cylindrical measurements to another cylindrical surface and from spherical measurements to another spherical surface1-7. In many cases the AUT is approximately a planar structure and it is desirable to calculate the hologram on a planar surface from cylindrical or spherical near-field or far-field measurements. This paper will describe a recently developed spherical hologram calculation where the farfield pattern can be projected on any plane by specifying the normal to the plane. The resulting hologram shows details of the radiating antenna as well as the energy scattered from the supporting structure. Since the hologram is derived from pattern data over a complete hemisphere, it generally shows more detail than holograms from planar measurements made at the same separation distance.

Limitations of Near-Field Back Projection for Phased Array Tuning Applications

Authors: Daniël Janse van Rensburg

Publication: AMTA 2001

Copyright Owner: NSI-MI Technologies

Simulated data is presented for a planar array to demonstrate the limitations of planar near-field back projections. It is well known that the result obtained in this way is of limited resolution and accuracy and these limitations are further illustrated through the data presented here. The impact of probe to AUT separation distance is shown as well as the correspondence between array excitation perturbations and that detected through the back projection technique. Results are shown for a simple iterative array excitation adjustment process. The purpose of this paper is to provide guidelines for the application of the planar near-field back projection technique.

Novel Spherical Near-Field Antenna Measurement Techniques Advance State-of-the-Art

Authors: A. Ray Howland, P.E., Carl W. Sirles, Michael H. Sewell

Publication: AMTA 2001

Copyright Owner: NSI-MI Technologies

Widespread deployment of cellular phones and use of wireless devices such as personal digital assistants, in-vehicle installs of Global Positioning System (GPS) receivers, and the upcoming deployment of mobile satellite digital audio has sprung a revitalized interest in faster, more affordable measurement techniques for antennas. This paper presents information on several new Spherical Near-field antenna measurement ranges developed by ATDS-Howland.