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AMTA Paper Archive

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.

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.

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.

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.

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.

Design of blended rolled edge for arbitrary rim shaped compact range reflectors
I.J. Gupta (The Ohio State University ElectroScience Laboratory),K. Ericksen (The Ohio State University ElectroScience Laboratory), W.D. Burnside (The Ohio State University ElectroScience Laboratory), November 1988

A procedure to design blended rolled edges for arbitrary rim shape compact range reflectors is presented. The reflector may be center-fed or offset-fed. The design procedure leads to continuous and smooth rolled edges and ensures small diffracted field from the junction between the paraboloid and the rolled edge. The performance of a compact range reflector designed using the prescribed procedure is also presented.

Transfer efficiency of the compact range
R.W. Kreutel (Scientific-Atlanta, Inc.), November 1988

Over the years formulations have been developed which provide an implicit measure of transfer efficiency of the compact range. Reasonable accuracy has been demonstrated for both antenna and RCS measurement applications. In general, however, these formulations require specific design details pertaining to the collimating reflector. In this note a more general formulation is examined in which efficiency is explicitly expressed in terms familiar to antenna engineers and which do not directly involve reflector parameters. Applications of this formulation are presented.

Parasitic multimode/corrugated (PMC) feed for a compact range
W.A. Schneider (Boeing Aerospace Company), November 1988

The radar cross section of large targets has previously been measured on large outdoor far field ranges. Due to environmental and security limitations of outdoor ranges, low cost indoor compact ranges are preferred. To optimize compact range performance and to minimize size, careful attention must be paid to the design of feeds which are required for the proper illumination of the reflector. This paper describes a new polarization diversified parasitic multimode/corrugated (PMC) feed for a compact range reflector. The performance attributes of the PMC feed are presented. The PMC feed provides several advantages over other known commercially available compact range feeds.

Precision compact range feed
K.R. Goudey (Harris Corporation GCSD),L.R. Young (Harris Corporation GCSD), November 1988

This paper describes how corrugated feed horns are designed for compact ranges with tight pattern control. Both the amplitude and phase of the horn pattern must be invariant over a wide frequency band. A horn synthesis computer program has been developed using the JPL HYBRIDHORN computer program as the analysis module which is driven by a Harris developed synthesis code (OPTDES). This paper also discusses launching techniques used to generate the HE(11) hybrid mode in the corrugated horn as well as design methods to eliminate ringing effects observed in both the input waveguide circuits and corrugated horns when used for RCS measurements.

Development of a small compact range facility
R.B. Dybdal (The Aerospace Corporation),Stewart G.E. (The Aerospace Corporation), November 1988

The development of a small compact range facility that has been integrated into an existing laboratory space is described. This facility uses a commercially available offset reflector with a 6 ft projected diameter and has sufficiently precise construction for operation at EHF frequencies. The edge diffraction degradation of the quiet zone is controlled by reducing the reflector edge illumination rather than using a complex edge treatment or a dual reflector design. Measured values of the quiet zone fields compare very well with calculated values. The facility can be used to measure antennas and radar targets whose dimensions do not exceed 20 in at high microwave and millimeter-wave frequencies. The low cost and simplicity of this compact range design are key features.

Analysis and measurements of horns in absorber-lined tunnels
G.E. Stewart (The Aerospace Corporation),R.B. Dybdal (The Aerospace Corporation), November 1988

The utility of absorber-lined tunnels to control the sidelobe levels of horns has previously been demonstrated. The use of such a tunnel gives the designer the option of designing a broadband feed, for example, and later tailoring the sidelobe level to meet a given specification. In this paper, a technique for calculating the radiation characteristics of a horn in an absorber-lined tunnel will be presented. The analysis is based on an absorbing phase screen approximation which has been used by one of the authors in analyzing the diffraction of signals around rocket plumes. Propagation through the tunnel is treated as if the wave travels through a sequence of layers in which the absorption depends on the transverse coordinates. The absorbing phase screen model will be developed, and then applied to the analysis of a Narda standard gain horn in a square tunnel which is lined with wedge absorbing material. For the determination of E and H-plane pattern cuts, a two dimensional model can be utilized. In order to determine the radiation pattern over the full range of theta and phi as is required for illuminating a reflector, a three dimensional model is needed. All calculations were implemented in Fortran on an IBM personal computer.

The Panelized approach to compact range construction
J. Cantrell (Harris Corporation), November 1988

The development of the Harris 1640 compact range required significant technical advances in developing a method of constructing a 70 foot reflector to a 0.005 inch RMS operational surface accuracy. A panelized approach is believed to be the only practical way to achieve this level of accuracy. Four technology areas had to be developed, adapted to this use, or have their current limits extended. A method was required for reducing the RF shaping data to individual panel contours. The reflector has no axis of symmetry thus each panel has a unique contour and the description of each contour requires complex mathematical interpolation. A new fabrication technique was needed to produce 0.002 inch RMS panels. Positioning and initially aligning the panels would require the adaptation of multiple theodolite techniques. The final setting of the panels would then require the use of a photogrammetric measurement system, the most accurate method available.







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