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AMTA Paper Archive

RCS analysis of targets from reconstructed images
E.V. Sager (System Planning Corporation),M.W. Mann (System Planning Corporation), November 1988

The ISAR image is a domain that possesses many of the spatial physical characteristics of the target. Certain procedures can be performed in the image domain that are equivalent to physical operations on the target. These operations include the ability to modify the amplitude of the scatterers that are represented in the image and, after performing these modifications, subjecting the image to an inverse transformation that recovers RCS data of the whole body as a function of frequency and aspect angle. The RCS plots obtained by transforming the edited image are representative of similar modifications made to the physical body and are of value in eliminating the need for many model modifications and retests in low-observable model development. This paper describes, using simulated and actual target data, some of the procedures that can be fruitfully applied in this type of analysis.

New near field RCS--and antenna--measurement techniques
V.J. Vokurka (March Microwave Systems B.V.), November 1988

In this paper a new system consisting of a single parabolic reflector and a point source will be presented. Such a system is capable of producing a cylindrical wavefront over a wide frequency range. Moreover, physically large text-zone dimensions can be realized. The principle of operation is identical to that of the near-field/far-field cylindrical scanning, however, the far-field antenna pattern or RCS response can be computed more efficiently by performing a simplified transformation procedure in one dimension only. It will be shown that such a system is suitable for both antenna and RCS measurements. Finally, experimental RCS data will be presented.

Measured performance of the Harris family of compact ranges
A.L. Lindsay (Harris Corporation GCSD),S.G. Russell (Harris Corporation GCSD), November 1988

This paper reports the quiet zone characteristics of the Harris family of compact ranges. Field probe measurements of systems having quiet zones of 3, 6, and 40 feet are presented. The quiet zones were characterized using a two way measurement with a trihedral corner reflector target. One way CW field probe measurements with an open ended waveguide are also presented for the Model 1606 range. A Discrete Fourier Transform (DFT) is imbedded in the test set software and provides an angle domain signature of extraneous signals illuminating the quiet zone. The two way range transfer functions of the Model 1603 and 1606 ranges are verified using calibrated spherical targets with the HP-8510 network analyzer operating as a time domain reflectometer.

Model 1640 - The Harris large compact range
H.R. Phelan (Harris Corporation GCSD), November 1988

Harris Corporation is in the final stages of implementing the Model 1640 Compact Range for The Boeing Corporation. This paper provides an overview of the development, fabrication, installation, and test activities on this very significant advance in the compact range state-of-the-art. This range represents a significant increase in quiet zone size over prior art. It features the wide dynamic range, low noise floor, and high quality quiet zone that is achievable using the Harris-proprietary shaped range technique. Another feature of this range is the completely panelized construction technique. This allows the production of very large, very precise reflector systems. Primary technical features of the Model 1640 are a 40 foot quiet zone, a -70 dBsm noise floor, and a frequency range extending from VHF to millimeter-wave frequencies.

A Serrated-edge virtual vertex compact range reflector
D.W. Hess (Scientific-Atlanta, Inc.),K. Miller (Scientific-Atlanta, Inc.), November 1988

In this presentation we consider the features and performance of a large serrated-edge compact range reflector. This is a straightforward innovation from earlier compact range reflectors. The virtual vertex reflector is a paraboloidal surface truncated to exclude the vertex. This layout provides the advantages of better use of reflector surface area, reduced feed blockage, and reduced feed backscatter. The design is made economical by the use of serrations.

Refractivity fluctuations on an RCS test range: comparative measurement, characterization, and implications for calibration procedures
D. Stein (LTV Aerospace and Defense Company),Paul Burnett (Holloman Air Force Base) Jack Smith (Arizona State University) David Williams (The University of Texas at El Paso), November 1988

The performance of an outdoor, ground-plane RCS measurement range can be degraded by fluctuations in the atmospheric reflectivity N. These fluctuations can introduce error into RCS measurements, particularly when they do not manifest in the radar return from the secondary calibration standard. A propagation anomaly study at the RATSCAT RCS range compares the N-fluctuations -- obtained from meteorological instruments and separately from RF receivers -- at several levels above the ground. The fluctuation mechanisms are discussed in terms of temperature lapse rates, "constant-N" cell sizes, wind velocity, and rough ground effects. The optimal RF sensor height for propagation anomaly indications is found to depend on the cell size. This has implications for the positioning of secondary calibration standards.

Calibration and normalization of windowed RCS images
L.R. Burgess (Flam & Russell, Inc.),C.T. Nadovich (Flam & Russell, Inc.), R. Flam (Flam & Russell, Inc.), November 1988

It is common practice to window RCS data prior to inverse Fourier transformation into an image. Windowing reduces image sidelobes at the expense of some loss of resolution. When the window shape is adjusted to give the best resolution-sidelobe tradeoff for the given application, however, the apparent RCS of features in the image varies unless the correct calibration of normalization is applied. This paper discusses the proper calibration and normalization techniques to use with RCS imaging. These techniques permit efficient generation of images that accurately depict the RCS of significant target features, independent of the data window shape.

Modern dynamic RCS and imaging systems
E. Hart (Scientific-Atlanta, Inc.),R.H. Bryan (Scientific-Atlanta, Inc.), November 1988

This paper presents a conceptual overview of the instrumentation system and signal processing involved in dynamic RCS and Imaging measurement systems.

A Wide band instrumentation radar system for indoor RCS measurement chambers
P. Swetnam (The Ohio State University),M. Poirier (The Ohio State University), P. Bohley (The Ohio State University), T. Barnum (The Ohio State University), W.D. Burnside (The Ohio State University), November 1988

An instrumentation radar system suitable for collection of backscatter characteristics of targets in an indoor chamber was built and installed in the Ohio State University ElectroScience Laboratory. The radar is a pulsed system with continuous coverage from 2 to 18 GHz, and spot coverage from 26 to 36 GHz. The system was designed to have maximum flexibility for various test configurations, including complete control of the transmit waveform, H or V transmit polarization, dual receive channels for simultaneous measurement of like and cross polarization, greater than 100 dB dynamic range, and convenient data storage and processing. A personal computer controls the operation of the radar and is capable of limited data reduction and display functions. A mini-computer is used for more widely sophisticated data reduction and display functions along with data storage. This paper will present details of the radar along with measured performance capabilities of the system.

A Near field focus procedure using compact range data
T-H. Lee (The Ohio State University ElectroScience Laboratory),W.D. Burnside (The Ohio State University ElectroScience Laboratory), November 1988

A near field focus procedure for image processing using near zone backscattered fields obtained in a compact range is presented in this paper. An array of defocussed feeds is used to illuminate a target in a compact range. The backscattered field received at each feed antenna with the target being stationary is compensated by a phase factor. These compensated signals are then summed coherently to obtain a cross range image of the target which indicates the location of the various scattering centers associated with the target. Numerical examples are presented to validate this technique.

Applications of autoregressive spectral analysis to high resolution time domain RCS transformations
E. Walton (The Ohio State University ElectroScience Laboratory), November 1988

Modern analysis techniques of radar scattering data or radar cross section (RCS) data often include transformation to the time domain for the purpose of understanding the specific scattering mechanisms involved or to isolate or identify specific scattering points. The classic technique is to transform from the frequency domain to the time domain using an inverse (Fast) Fourier Transform (IFFT). Often, however, the scattering centers are too close together to resolve or the requirement for accuracy in the measurement of the differential time delay is too high given the IFFT inverse bandwidth. This paper presents a technique for determining the time domain response of a radar target by processing the data using modern autoregressive (AR) spectral analysis. In this technique, the scattering from a radar target in the high frequency regime is shown to be autoregressive. This paper will show examples using the maximum entropy method (MEM) of Burg.

Electromagnetic and structural considerations in target support design
M.L. Wolfenbarger,P.E. Amador, November 1988

This paper will address low RCS target mounting systems. Structural and electromagnetic aspects will be considered. The 4:1 vs the 7:1 ratio ogival shell pylons will be evaluated with consideration given to structural integrity, electromagnetic scattering, and positioner size. Measured and analytic data will be used in these evaluations.

RCS calculations for the optimization of target pylons
M. Naor (M.O.D., Haifa, Israel),A. Michaeli (M.O.D., Haifa, Israel), D. Dvorzhetski (M.O.D., Haifa, Israel), R. Sinai (Orbit, Advanced Technologies), November 1988

The monostatic RCS of ogival tilted pylon was calculated in a two stage computational process. First, a two-dimensional model of an infinite cylinder of ogival cross-section was employed. At the second stage, the effects of finite length and inclination were incorporated. The RCS was predicted by two independent methods, namely, the method of equivalent currents and the method of moments. Excellent agreement between the results of the two methods was found in the overlap domain of their respective validity. The results indicate a weak dependence of the RCS on the ogive ratio. Similarly, it was found that in the case of an infinite straight ogival cylinder the effect of frequency variation is negligible. The main contribution to RCS reduction is derived from the finiteness of the pylon and its tilt. It also becomes evident that beyond a certain tilt angle the marginal decrease of RCS does not justify the increasing mechanical complexity.

RCS errors due to target support structure
W.T. Wollny (Quick Reaction Corporation), November 1988

The deleterious effect of tilting the pylon on the measured RCS of a low level target is shown. A two scatterer computer model is developed to demonstrate the harmful effect of the pylon on the target signature. Predicted RCS plots are provided for the pylon to target ratios of -20, -10, 0, and +10 dB. The familiar error curve for two interfering signals is shown as applicable to bound the RCS errors of two scatterers. A method for computing the pylon RCS from linear motion RCS measurements is described with sample data plots. A knowledge of the pylon RCS allows the inclusion of measurement confidence levels on all RCS plots which is very valuable to the analyst. All radar data that is below the known RCS of the target support structure can be blanked from the plotted data to prevent confusion since these RCS values are an artifact of the measurement system and are not a true representation of the target RCS.

Target mounting techniques for compact range measurements
H. Shamansky (The Ohio State University),A. Dominek (The Ohio State University), November 1988

The compact range provides a means to evaluate the radar cross section (RCS) of a wide variety of targets, but successful measurements are dependent on the type of target mounting used. This work is concerned with the mounting of targets to a metal ogival shaped pedestal, and in particular focuses on two forms of mounting techniques: the "soft" (non-metallic) and "hard" (metallic) mounting configurations. Each form is evaluated from both the mechanical and electromagnetic viewpoints, and the limitations associated with each type are examined. Additional concerns such as vector background subtraction and target-mount interactions are also examined, both analytically and through measurements performed in the ElectroScience Laboratory's Anechoic Chamber.

The Radar image modeling system
R. Renfro (David Taylor Research Center), November 1988

The characteristics of a unique indoor RCS modeling facility are described. The David Taylor Research Center (DTRC) has implemented an indoor, over-water radar cross section measurement facility. Major components of the facility are the DTRC Seakeeping Basin, an imaging radar, an underwater target mount and rotator, a calibration system, and video monitoring equipment. Initial operational capabilities include dynamic pulse-to-pulse polarization-agile measurements at X and Ku bands, elevation angles from grazing to 7 degrees, maximum target length of 50 feet, and simulated sea states adjustable between state 0 and state 3. Several data products are available, including high-resolution inverse synthetic aperture radar images. Eventual capabilities will include extended elevation angles up to 30 degrees, frequencies to beyond 100 GHz, and SAR imagery.

Angular domain analysis of shaped compact range field probe data
M.L. Foster (Harris Corporation GCSD), November 1988

A simple computer program which performs a direct calculation of the Discrete Fourier Transform (DFT) was written to generate the plane wave spectrum of a compact range from sampled field probe data. This program was used to analyze idealized quiet zone fields, computer predicted quiet zone fields and measured field probe data. Data from this analysis is presented along with suggestions for the correct interpretation of the results.

A Planewave spectral range probe
R.D. Coblin (Lockheed Missiles & Space Co.), November 1988

The weakest link in antenna metrology is the antenna range itself. Unknown reflections can cause large errors in antenna measurements and can change unpredictably. Conventional range probing methods typically provide a go/no go test with very little information about the location of the range scatterers. A number of techniques show promise for locating antenna range scattering centers. This paper describes the theory of a probe analysis method being implemented at Lockheed Missiles and Space Company. The method is based on planewave spectral analysis. A specialized probe system to test the planewave spectral theory will be described.

A Model for the quiet zone effect of gaps in compact range reflectors
D.N. Black (Georgia Institute of Technology),E.B. Joy (Georgia Institute of Technology), November 1988

A model is presented for the analysis of gaps in reflector panels. In this model, Butler's method of expanding fields in terms of a series of Chebyshev functions is used to determine the gap aperture fields. These aperture fields are then transformed into the quiet zone to obtain the final scattered field expression. Because of simplifying approximations, this method is only valid for gap widths that are less than both the panel dimensions and one-third the operating wavelength. Quiet zone fields are calculated for compact range antennas modeled as parabolic cylinders using this method. An RMS sum of the scattered fields is used to determine the worst case effects of frequency, gap width and differing number of panel gaps on peak-to-peak quiet zone amplitude ripple. Results are presented for a large range with a 75 foot diameter reflector and a smaller range with a 18.75 foot diameter reflector.

Analysis of compact range reflectors with serrated edges
K. Miller (Scientific-Atlanta, Inc.),R.W. Kreutel (Scientific-Atlanta, Inc.), November 1988

The use of serrated edge treatment in the design of a compact range collimating reflector is one method of mitigating the effects of edge diffraction on quiet zone performance. In this note a physical optics analysis is applied to the serrated reflector. The computational procedure is described and several results are presented. In particular, computed results are presented for the S-A Model 5755 compact range reflector and compared with experiment.







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