AMTA Paper Archive
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Dynamic Radar Cross Section Measurements
Unique instrumentation is required for dynamic (in-flight) measurements of aircraft radar cross section (RCS), jammer-to-signal (J/S), or chaff signature. The resulting scintillation of the radar echo of a dynamic target requires special data collection and processing techniques to ensure the integrity of RCS measurements. Sufficient data in each resolution aspect cell is required for an accurate representation of the target's signature. Dynamic RCS instrumentation location, flight profiles, data sampling rates, and number of simultaneous measurements at different frequencies are important factors in determining flight time. The Chesapeake Test Range (CTR), NAVAIRWARCENACDIV, Patuxent River, Maryland, is a leader in quality dynamic in-flight RCS, J/S ratio, and chaff measurements of air vehicles. The facility is comprised of several integrated range facilities including range control, radar tracking, telemetry, data acquisition, and real-time data processing and display.
Modeling System Reflections To Quantify RCS Measurement Errors
RCS measurement accuracy is degraded by reflections occurring between the feed antenna, the range, and the radar subsystem. These reflections produce errors which appear in the image domain (both 1-D and 2-D). The errors are proportional to the RCS magnitude of the target under test and they are present in each of the typical range calibration measurements. Current 2-term error models do not predict or account for the above errors. An improved 8-term error model is developed to do so. The model is based on measurable reflections and losses within the range, the feed antenna, and the radar. By combining the improved error model with the commonly used 2-term RCS range calibration equation, we are able to quantify the residual RCS errors. The improved error model is validated with measured results on a direct illumination range and is used to develop specific techniques which can improve RCS measurement accuracy.
Proposed analysis for RCS measurement uncertainty
From a study of several radar cross section (RCS) measurement facilities, we identify significant sources of uncertainty and develop methods for estimating their effect. Out goal is to provide a "reasonable" and uniform formalism for evaluating RCS measurements which can be used on a variety of test ranges to produce comparable estimates of uncertainty.
Study of simple geometric shapes by polarimetric radar
New results from complete scattering matric measurements on string-suspended simple geometric shapes - from the Boeing 9-77 compact range - are presented for the first time.
Application of genetic algorithms to the optimisation of wideband Jaumann radar absorbers for normal and oblique incidence
The design of wide-band, multi-layer radar absorbing materials involves the solution of what is essentially an N-dimensional optimization problem. Genetic algorithms appear to offer significant advantages over conventional optimization techniques for this type of problem due to their robustness and independence of performance function derivatives. To illustrate their use, the paper considers the optimum design of wideband, multi-layer, Jaumann radar absorbers for normal and oblique incidence.
Probe compensation characterization and error analysis in cylindrical near-field scanning
A novel computer simulation methodology to properly characterize the role of probe directivity/pattern compensation in cylindrical near field scanning geometry is presented. The methodology is applied to a linear test array antenna and the JPIJNASA scatterometer (NSCA1) radar antenna. In addition, error analysis techniques of computer simulation and measured have been developed to determine the achievable accuracy in pattern measurements of the NSCAT antenna in cylindrical near field.
Analysis of amplitude dispersion in radar scattering using preconditioned linear prediction
Radar scattering can be modeled as a sum of contributions from a finite number of canonical scattering centers. These canonical scattering centers (edges, corners, specular points) all have different amplitude behavior as a function of frequency. We completely characterize this behavior with a single parameter in a parametric model of the scattering data. The estimation of this amplitude dispersion parameter along with down range location and rela tive amplitudes is presented.
Joint STARS phased array antenna measurements at IF
Norden Inc. has developed and instrumented its JSTARS 1000' Outdoor Antenna Range with a multi-port antenna measurement system designed to acquire antenna data (patterns and other related signals) at the antenna's respective radar system's intermediate frequency (IF). The measurement system utilizes the JSTARS RF microwave receivers attached to the multiple channels of the JSTARS antenna. These receivers obtain the RF signal from these multiple channels and provide the IF signals to the measurement system.
High speed multi-frequency antenna measurements in the MDTI radar measurement center
This paper demonstrates a high speed antenna measurement capability recently developed in the MDTI Radar Measurement Center. Originally constructed as a Radar Cross Section facility, the RMC has added the capability to measure antenna patterns on apertures up to 40-feet in length in the far field. Data will be presented to demonstrate system performance through the use of modern output formats, such as global plots and videotape presentations.
Three-dimensional radar cross section imaging
Three-dimensional imaging capability has recently been added to METRATEK's Model 200 RCS Diagnostic Radar. This paper describes the rationale and methodology for producing three dimensional images and gives sample images taken with the system.
Enhanced high resolution radar imaging
Radar with the 2-D Fourier trans- form of the scattered field data in frequency and/or have poor resolution. A modified brid method and a modified 2-D AR technique are proposed to high radar images us- limited backscattered field data. The final image presents the scattering properties of the target in a quantitative way. The peaks in the image represents the positions of centers contributing to the backscattered field. Furthermore, the amplitudes of the peaks correspond to the intensities of the scattering centers.
Radar cross section calibration measurements using helicopter suspended spheres
The Naval Command, Control and Ocean Surveillance Center, Research, Development, Test and Evaluation Division (NRaD) is tasked by the Navy to collect and evaluate full-scale radar cross section (RCS) measurements on ships and aircraft. The Radar Branch at NRaD, operates a radar range west of Pt Loma, San Diego, CA. This radar range has been used to collect X-band and Ku-band calibrated data on Naval ships for the past seven years. The NRaD radar calibration helicopter procedures are the focus of this paper. Using helicopters to suspend and measure "isolated" spheres in space as the primary reference is a major calibration element. A 1700-ft Kevlar line is used to suspend the sphere from the helicopter. This length of line is sufficient to isolate the helicopter from the sphere; thus, the helicopter is not in the significant antenna sidelobes.
RCS doppler measurements at millimeter wave frequencies
A versatile millimeter wave imaging radar is presented to conduct polarimetric doppler as well as wide band RCS measurements. The aim of the system is not only to acquire doppler measurements of determine the distance of an object but also to generate image-like information for classification purposes. A hardware gate controller is incorporated in the system to perform pulsed measurements. This controller can drive three different frequency extension modules covering frequency ranges from 8 to 18 GHz, 70 to 80 GHz and 75 to 77 GHz respectively. In all bands, dual polarized horns are used to allow fully polarimetric measurements. A network analyzer and a FFT analyzer are used as receivers. For both concepts the advantages and disadvantages are discussed. The transmit and the receive antenna are mounted on a positioner. Thus, a radar image using the real aperture of the antennas can be generated by mechanical scanning in azimuth and elevation.
Experimental results of strategic target identification by resonant radar cross section measurements
RCS measurements of representative strategic targets in the resonant scattering regime are presented in this paper. The frequency and aspect dependent RCS signatures of various targets are shown to have close agreement to method-of-moment calculations which are based upon the known target shape and composition. Using the resonant scattering signatures, non-cooperative target recognition can be performed with high confidence using a discrete frequency sampling approach. The target set included cones, spheres, and canonical shapes which have been characterized in the VHF and UHF bands. Measurements made at the Lockheed Space Missile Company Rye Canyon facility have recorded calibrated RCS of representative hardware as a function of both frequency and aspect in the resonant region. These data compare well with prediction, and their use for non-cooperative target recognition will be explained. This effort is being conducted to develop signature models, laboratory measurements and useful discrimination algorithms which exploit the frequency variation of the resonant scattering RCS.
Analysis of wedge radar cross section
The need for practical solutions to radar scattering in high-frequency regime have led to the development of a number of approximation methods. The high-frequency asymptotic methods use approximations based on physical optics (PO), geometrical theory of diffraction (GTD) or physical theory of diffraction (PTD) and their variations. Radar scattering from electrically large conducting surface includes traveling surface wave contributions which are not accounted by the high-frequency asymptotic methods. A hybrid method integrating GTD and traveling wave theory (TW) is used for verification and to illustrate important scattering mechanisms that influence radar cross section (RCS) of a wedge. Analysis of the wedge RCS signature identifies significant contributions of the traveling surface waves to the total RCS. Both measured and predicted RCS of the wedge are considered. Using hybrid GTD-TW method very good agreement between the predicted and measured RCS patterns is observed for all angles.
Radar absorbing material thermal characteristics
The Benefield Anechoic Facility, Edwards AFB, California contains a large anechoic chamber for avionic integration test and evaluation. Because of the large chamber size, operational tests can require high-power aircraft radar emissions. To define the range of energy safely accommodated by currently installed radar absorbing material (RAM), a detailed analysis was performed and the results presented. The incident radar energy generates a heat transfer to the RAM. The RAM boundaries dissipate heat through convection, conduction, and radiation. A finite-difference solution demonstrates the temperature distribution in the material varies with the angle and polarization of the incident electric field. Discussions include the use of the RAM thermal characteristic's pretest evaluation to improve operating capability determinations and to facilitate assessment of customer requirements.
High resolution one dimensional radome characterization
In this paper radome evaluation based on high resolution imaging techniques is described. It allows anomalies on a large radome to be detected very accurately. It required scanning of the radome through only a small angular section using an inverse synthetic aperture radar approach. The one dimensional image formed from field data provides a linear distribution of scattering source locations. The calibration necessary to compensate for the translation and rotation of the antenna is discussed. The technique is demonstrated through measurements performed on a large fibre glass radome.
Combined pulsed/CW and pulsed-IF instrumentation radar system, A
In response to evolving USAF RCS measurement requirements, Lintex has developed a combined Pulsed/CW and Pulsed-IF instrumentation system for use at the Advanced Radar Cross Section Measurement Range. This instrumentation system, one of Lintek's Model 500 Series, couples the simplicity and high signal-to-noise ration of Pulsed/CW measurements with the flexibility and precise clutter rejection of Pulsed-IF systems. In this paper, a direct comparison of the Pulsed/CR and Pulsed-IF performance is presented. The theoretical sensitivity and throughput of the system as a function of duty cycle in each mode is calculated and compared to the measured results. The Pulsed-IF system is found to have better sensitivity and stability for short-range measurements due to the high PRF capability of this receiver. The Pulsed-IF mode of operation also offers much better sensitivity for measurements made at longer ranges, for which the duty-cycle losses of the Pulsed/CW mode become excessive. The wideband Pulsed-IF mode is also preferred in high-background environments, since precise time-gating may be used to reduce the clutter return. In areas of high RFI, the Pulsed/CW radar system has provided better results due to the narrow receiver bandwidth.
Compact modular instrumentation radar system, A
A compact modular instrumentation radar system has been developed for antenna, RCS, and general RF measurements. The MMS-420 system consists of a single, rack mounted, programmable mainframe controller and display into which a wide range of RF, IF and signal processing modules can be installed. A family of external RF modules has also been developed to support measurements from VHF through millimeter-wave bands. It is designed to function as a stand-alone measurement system, or interface with network analyzers and other external processing equipment. The hardware and software are easy to customize for specialized measurement applications.
Band concatenation for higher resolution RCS imaging
Radar Cross Section (RCS) measurements are often performed in discrete frequency bands for a variety of reasons. Although some indoor ranges are capable of performing very wide-band measurements (with bandwidths up to or exceeding 9: 1), some are designed with very rigid illumination requirements on the coIIimating reflector(s) that can only be met over a narrow band. In addition, the bandwidth available on most outdoor ranges is limited by "ground plane" effects which make it impossible to maintain an adequate broadband field over the target. Often, RCS measurements are limited to half an octave at most. Since resolution in RCS imaging is directly proportional to bandwidth, there exists a need for concate nati ng several discrete bands of measurements into a single continuous band. This resulting band must be free of both amplitude and phase discontinuities that would affect the quality of the resultant image. This paper discusses the sources of discontinuities between measured bands on both indoor and outdoor ranges, and provides algorithms for removing them using linear filtering methods. Data is presented from an outdoor range illustrating the results on targets up to 70-feet in length.
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