Automated Three-Antenna Polarization Measurements using Digital Signal Processing

Author: John R. Jones
Publication: AMTA 1985
Copyright Owner: NSI-MI Technologies

In this paper we present a three-antenna measurement procedure which yields the polarization of an unknown antenna to an accuracy comparable to that of the improved method of Newell. The complete method is based on step-scan motion of the two polarization axes on which the antenna pairs are mounted. As a special case this step-scan procedure includes the usual single axis polarization pattern method of polarization measurement.

This three-antenna polarization measurement method can be readily automated and is carried out straightforwardly with the assistance of a minicomputer for data acquisition and data reduction. The data reduction method is based on conventional digital Fourier transform techniques and has the advantage of inherent noise rejection. It utilizes a large number of sample points which greatly over determine the parameters to be measured.

The method has been verified experimentally with measurements made on multiple overlapping sets of three antennas, as is conventional for this kind of procedure. The data are presented for broad-beam antennas of the type use as near field probe horns.


Inverse Synthetic Aperture Imaging

Authors: Dan Slater
Publication: AMTA 1985
Copyright Owner: NSI-MI Technologies

The accurate measurement of radar target scattering properties is becoming increasingly important in the development of stealth technology. This paper describes a low cost imaging Radar Cross Section (RCS) instrumentation radar capable of measuring both the amplitude and phase response of low RCS targets. The RCS instrumentation radar uses wide band waveforms to achieve fine range resolution providing RCS data as a function of range, frequency and aspect. With additional data processing the radar can produce fully focused Inverse Synthetic Aperture Radar (ISAR) images and perform near field transformations of the data to correct the phase curvature across the target region. The radar achieves a range resolution of 4 inches at S-band and a sensitivity of -70 dBsm at a 30ft. Range.


Near Field Test Facility Design

Authors: Dan Slater
Publication: AMTA 1985
Copyright Owner: NSI-MI Technologies

Lesson learned in the design of large, planar near-field ranges used at millimeter wavelengths are described. Specific issues include facility design, RF equipment, scanner design, dynamic position measurement, servo control and software requirements.


Calibration techniques used in the Sandia National Laboratories Scatter Facility

Authors: Marion c. Baggett, Charles M. Luke, Billy C .. Brock, Ronald D. Bentz
Publication: AMTA 1985
Copyright Owner: NSI-MI Technologies

This paper briefly discusses the calibration techniques used in the Sandia National Laboratories Radar Cross-Section Test Range (SCATTER)a We begin with a discussion of RCS calibration in general and progress to a description of how the range, electronics, and design requirements impacted and were impacted by system calibrationa Discussions of calibration of the electronic signal path, the range reference used in the system, and target calibration in parallel and cross-polarization modes follow. We conclude with a discussion of ongoing efforts to improve calibration quality and operational efficiency. For an overview description of the SCATTER facility, the reader is referred to the article Sandia SCATTER Facilitv, also in this publication.


Spherical Near-Field Thermal Drift Correction using a return to peak Technique

Authors: G. Bruce Melson, Doren W. Hess, John R. Jones
Publication: AMTA 1985
Copyright Owner: NSI-MI Technologies

Over the long periods of time needed to acquire spherical near-field data, thermal drift of the system can cause errors in the measurement. The effect of thermal-drift can be removed, if it is monitored during the scanning process. This is accomplished by periodically returning the probe to the near-field peak during acquisition. The same point is re-measured upon each return; and the variations in phase and amplitude are used to produce a correction factor which is applied to each point in the near-field data file. This paper describes the return-to-peak method and the correction algorithm. Experimental results will also be presented.



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