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It is possible to build a very inexpensive radar which transmits wide band radio noise. On receive, the signal is cross correlated with a delayed version of the transmitted signal. In this paper we will discuss the design and operation of a UWB noise radar which was installed in the OSU compact RCS measurement range. Scattering measurements were made for a number of targets over 360 degrees of aspect angle. Calibration was performed, and then the data converted to ISAR images. Example ISAR images will be shown.
The U.S. Air Force is currently building deployable Diagnostic Imaging Radar (DIR) systems to perform quality control (QC) low-observable (LO) measurements of the F-117 fighter. Each system is a stepped-pulse frequency synthetic aperture radar (SAR) built by System Planning Corporation (SPC) combined with analytical software developed by MIT Lincoln Laboratory for generating radar images that will be interpreted to ensure LO integrity. The DIR systems will be used at fixed operating sites such as the F-117A main operating base, the F-117A maintenance depot, and any sites worldwide to which the aircraft may deploy. The F-117A DIR is the first field-level deployable radar cross section (RCS) measurement system for an operational weapon platform that is designed for use by the maintenance squadron. This paper discusses the critical issues of QC measurements for LO systems. It also describes the test requirements that are driving the development of DIR, and highlights the radar and SAR positioner requirements. Also presented is an overview of the diagnostic software and the algorithms used for detecting RCS anomalies and predicting maintenance actions for problem correction by flight-line crews.
Millimeter Wave (MMW) Radar Cross Section (RCS) measurements of full scale ground vehicles are used to develop and validate scattering models for smart weapons applications (target detection, discrimination and classification algorithms) and Hardware-in-the-Loop (HITL) missile simulations. This paper describes a series of MMW RCS measurements performed at Range C-52, Eglin AFB FL on a T-72M in a field environment using an exiting instrumentation radar (with slight modifications to allow for accurate height adjustment) and in-scene phase reference. The test methodology, instrumentation systems, 3-D Imaging Algorithm and sample data sets at 35 and 95 GHz will be presented as well as a detailed sensitivity analysis and discussion of error effects.
Radar images obtained using an adaptive finite impulse response (FIR) filter are compared with the radar images obtained using extrapolated scattered field data. The scattered fields of an experimental target and an airborne target are used in radar imaging. In adaptive FIR filtering, instead of fixed weights, variable weights are used in radar imaging. In this work, adaptive sidelobe reduction (ASR) technique is used to obtain the variable weights. Also, scattered field data extrapolation is carried out using forward backward linear prediction. It is shown that is the data extrapolation is successfully carried out by a factor of two or more, than the radar images obtained using the extrapolated scattered field data have better resolution than the radar images obtained using the adaptive FIR filters.
In recent years there has been much interest in developing low frequency radar cross section (RCS) measurement capability indoors. Some of the principal reasons for an indoor environment are high security, all-weather 24-hour operation, and low cost. This paper describes recent efforts to implement VHF/UHF RCS measurement capability down to 100 MHz using the large compact-range collimator in the Bistatic Anechoic Chamber (BAC) at Point Mugu. The process leading to this capability has given rise to a number of technical insights that govern successful test results. An emphasis is placed on calibration and processing methodology and on measurement validation using long cylindrical targets and comparing the results with method-of-moment computer predictions and with measurements made at other facilities.
A folded compact range configuration has been developed at the Sandia National Laboratories’ compact range antenna and radar-cross-section measurement facility as a means of performing indoor, environmentally-controlled, far-field simulations of synthetic aperture radar (SAR) measurements of distributed target samples (i.e. gravel, sand, etc. ). In particular, the folded compact range configuration has been used to perform both highly sensitive coherent change detection (CCD) measurements and interferometric inverse-synthetic-aperture-radar (IFISAR) measurements, which, in addition to the two-dimensional spatial resolution afforded by typical ISAR processing, provides resolution of the relative height of targets with accuracies on the order of a wavelength. This paper describes the development of the folded compact range, as well as the coherent change detection and interferometric measurements that have been made with the system. The measurements have been very successful, and have demonstrated not only the viability of the folded compact range concept in simulating SAR CCD and interferometric SAR (IFSAR) measurements, but also its usefulness as a tool in the research and development of SAR CCD and IFSAR image generation and measurement methodologies.
Radar cross section (RCS) range characterization and certification are essential to improve the quality and accuracy of RCS measurements by establishing consistent standards and practices throughout the RCS industry. Comprehensive characterization and certification programs (to be recommended as standards) are being developed at the National Institute of Standards and Technology (NIST) together with the Government Radar Cross Section Measurement Working Group (RCSMWG). We discuss in detail the long term technical program and the well-defined technical criteria intended to ensure RCS measurement integrity. The determination of significant sources of errors, and a quantitative assessment of their impact on measurement uncertainty is emphasized. We briefly describe ongoing technical work and present some results in the areas of system integrity checks, dynamic and static sphere calibrations, noise and clutter reduction in polarimetric calibrations, quiet-zone evaluation and overall uncertainty analysis of RCS measurement systems.
The RATSCAT Radar Cross Section (RCS) measurement facility at Holloman AFB, NM is working to satisfy DoD and program office desires for certifies RCS data. The first step is to characterize the Low Frequency portion of the RATSCAT Mainsite Integrated Radar Measurement System (IRMS). This step is critical to identifying error budgets, background levels, and calibration procedures to support various test programs with certified data. This paper addresses characterization results in the 150 – 250 MHz frequency range. System noise, clutter, background and generic target measurements are presented and discussed. The use of background subtraction on an outdoor range is reviewed and results are presented. Computer predictions of generic targets are used to help determine measurement accuracy.
In 1993, we presented the newly completed compact range and tapered chamber facility [1]. As part of this presentation, the issue of “range certification” was presented. This paper will discuss the work that we have done with the compact range for radar cross section (RCS) measurement acceptance. For customer acceptance, we had to “prove” that the compact range made acceptable measurements for the fixtures and apertures involved. Schedule and funding did not permit the full exploitation of the uncertainty analysis of the chambers, not was it felt to be necessary [2]. The determination of our range capabilities and accuracy was based on system parameters and target measurements. Targets that were calculable either in closed form solutions (spheres) or by numerical methods (cylinders and rods) were used. Finally, range to range comparisons with the Rye Canyon Facility [3] of a standard target was used. The range to range comparison proved especially difficult due to customer exceptions, feed differences, and target mounting. This paper will discuss the “success” criteria applied, the procedures used, and the results. The paper will close with a discuss of RCS standards and the range certification process.
It is shown that for dispersive scatterers, one cannot relate the intensity of the spatial response in the radar image to a particular location on the scatterer. For such cases, an imagery capable of characterizing both the spatial (dominant scattering centers) as well as spectral (resonant modes) wave objects. In the new image reconstruction, first a focusing point is selected for the image. The section of the image close to this focusing point provides good spatial resolution. As one moves away from the focusing point, the utilized bandwidth is reduced to provide good spectral resolution. The capabilities of the proposed imagery are illustrated using several examples.
In this paper we present a recently-developed adaptive method for decomposing radar signals into a wide range of physically meaningful mechanisms. The signal decomposition we will pursue is based on a set of functions referred to as “atoms” in the signal processing literature. These atoms can be derived from disparate mechanisms such as scattering center responses given by the Geometric Theory of Diffraction (GTD), which are localized in range, and resonance phenomena, which are localized in frequency. The atoms populate a “dictionary” of waveforms which are used to decompose radar signals. Traditional Fourier methods have restricted the class of atoms solely to harmonic exponentials. In this paper, we consider a number of signal decomposition methods. We chose a method based on the Basis Pursuit procedure of Chen and Donoho [1],which uses an L1 norm as opposed to a least squares approach to search the dictionary. We chose this technique because of its sparsity of representation and convergence properties. We will show results of this technique applied to numerically simulated data and show that disparate scattering mechanisms can be isolated and identified in the radar data.
To accurately measure static or dynamic Radar Cross Section (RCS), one must use precise measurement equipment and test procedures. Recently, several DoD RCS ranges, including the Advanced Compact RCS Measurement Range at Wright-Patterson AFB, established procedures to estimate measurement error. Working cooperatively with the National Institute of Standards and Technology (NIST), Wright Laboratory established a baseline error budget methodology in 1994. As insight was gained from the error budget process, we noted that many common RCS measurement calibration techniques are subject to a wide variety of potential error sources. This paper examines two common so-polarized calibration devices (sphere and squat cylinder), and discussed techniques for evaluating calibration induced errors. A rigorous “double calibration” methodology is offered to track calibration measurement error. These techniques should offer range owners fairly simple methods to monitor the quality of their primary calibration standards at all times.
The calibration of nonreciprocal radars has been studied extensively. A brief review of known calibration techniques points to the desirability of a simplified calibration procedure. Fourier analysis of scattering data from a rotating dihedral allows rejection of noise and background contributions. Here we derive a simple set of nonlinear equations in terms of the Fourier coefficients of the data that can be solved analytically without approximations or simplifying assumptions. We find that independent scattering data from an additional target such as a sphere is needed to accomplish this. We also derive mathematical conditions that allow us to check calibration data integrity and the correctness of the mathematical model of the scattering matrix of the target.
Dynamic ground-to-air measurement of aircraft RCS has several advantages over static measurements. The target may be measured in flight configuration and the support pylon is eliminated. Although dynamic RCS imagery has been performed since the late 1970s, the cost and complexity of such measurements have limited their utility for routine testing. In this paper, an easily deployable ground-to-air radar imaging system developed by Aeroflex Lintek is presented. This system forms images of aircraft in straight flight, requiring no on-board instrumentation or special pilot training. The radar system, flight profiles, and processing tools required for generating images of aircraft in flight are presented, along with examples of measured target data.
The Hughes Space and Communications Company (HSC) has recently undertaken the task to modify a RCS range once operated by Hughes Radar and Communications Systems, to accommodate the testing of Satellite Antennas. This measurement facility's configuration, design and current status will be discussed herein. This RCS range is located in El Segundo, California.
A portable system for measuring the RF environment at remote sites is described. A frequency range between 500 MHz and 18 GHz is covered by this system. The design, calibration and use of this system are discussed.
The imaging of radar targets is typically accom plished by measuring the radar cross section (RCS) of the target as a function of frequency and az imuth angle. We measure a third dimension of the RCS by tilting the target and collecting data for conical cuts of the RCS pattern. This third dimension of data provides the ability to estimate the three-dimensional location of scattering centers on the target. Three algorithms are developed in order to process the three-dimensional RCS data.
New windows which allow the user to select the level of sidelobe suppression near the DFT resolution limit are reported. By a parametric study, we identify the truncated Lorentzian and Gaussian functions as better choices compared with the popular Hann windows.
The Hughes Space and Communications Company (HSC) has recently undertaken the task to modify a RCS range once operated by Hughes Radar and Communications Systems, to accommodate the testing of Satellite Antennas. This measurement facility's configuration, design and current status will be discussed herein. This RCS range is located in El Segundo, California.
RCS data measured under near-field conditions is corrected to the far-field. The algorithm uses the HUYGEN's principle approach. The processing technique is describes and validates using anechoic chamber data and simulations taken on flat plate target at a distance from the radar R << 2D2/A, where D is the target cross range extend and A the wavelength. Good agreement with the theoretically predicted far-field RCS patterns is obtained.