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In order to have definitive measurement traceability according to, ANSI-Z-540, a radar cross section measurement facility must have solid traceability to a known and accepted measurement standard. The Air Force Research Laboratory choose short right circular cylinders as calibration standards for their facilities. We describe a general RCS uncertainty analysis technique, and apply the method to our calibration standards to establish absolute traceability to a known standard. Though applied to cylinders in the current paper, the uncertainty method is general enough for any arbitrary target
Boeing is currently pursuing certification of their 9-77 indoor compact range facility as a voluntary industrial participant in the ongoing DoD/NIST RCS certification demonstration program. In support of that process, V EI has applied a novel statistical method for analysis to VHF measurements of a canonical target from the Boeing 9-77 range. The dominant error sources in the range were identified and categorized according to their dependence on frequency, aspect angle, and the target under test. Range characterization data were collected on canonical targets and then used to estimate the statistical parameters of each of the errors. Finally, these were incorporated into expressions for the combined RCS measurement uncertainty for a test body whose RCS exhibits many of the characteristics of modern, high-value targets. The results clearly demonstrate the importance of accounting for the target-dependence of the errors and the bias they introduce into the overall uncertainty.
This paper describes how ANSI standard Z-540 [l,2,3] was applied in a DoD demonstration project to organize radar cross section (RCS) range documentation for the Air Force Research Laboratory Advanced Compact Range (ACR) and Patu:xent River Atlantic Test Range (ATR) Dynamic RCS measurement facility. Both parts of this paper represent a follow-up report on the DoD demonstration program introduced at AMTA 97 [4]. In June 2000, the DoD Range Commanders Council Signature Measurement and Standards Group (RCC/SMSG) certified that these two facilities met the ANSI-Z-540 documentation standards established by the DoD demonstration project. Since AFRL plans to require mandatory ANSI-Z-540 compliance for DoD contractors performing RCS measurements with AFRL after January 1, 2004, the review process described in this paper will be the likely model for industrial compliance. After a brief review of the ANSI-Z-540 standard, Part 1 of this paper will outline the certification review process and discuss the outcomes, results, and lessons learned from the DoD demonstration program from the perspective of the AFRL range and volunteer range reviewers.
This paper describes how ANSI/NCSL standard Z- 540 [1, 2] was applied in a DoD demonstration project to organize radar cross section (RCS) range documentation for the Air Force Research Laboratory (AFRL) Advanced Compact Range (ACR) and the Naval Ai:r Warfare Center - Aircraft Division (NAWC-AD) Atlantic Test Range (ATR) Dynamic RCS measurement facility. Both parts of this paper represent a follow-up report on the DoD demonstration program introduced at AMTA 97 [3]. In June 2000, the DoD Range Commanders Council Signature Measurement and Standards Group (RCC/SMSG) certified that these two facilities met the ANSI/NCSL Z-540 documentation standards established by the DoD demonstration project. Since AFRL plans to require mandatory ANSI/NCSL Z- 540 compliance for DoD contractors performing RCS measurements with AFRL after January 1, 2004, the review process described in this paper will be the likely model for industrial compliance. Part I of this paper contained a brief summary of the ANSI/NCSL Z-540 standard, outlined the certification review process and discussed the outcomes, results, and lessons learned from the DoD demonstration program from the perspective of the AFRL range and volunteer range reviewers. Part II will discuss the review process as it applied to ATR, as well as the outcomes, results, and lessons learned.
Nowadays, highly accurate antenna pattern and RCS measurements are performed in compensated compact range test facilities, which fulfil the stringent space requirements for measurements up to 500 GHz and more. As the suppression of diffracted fields from the reflectors mainly determine the quiet zone field performance, the reflector edge treatment is an important design parameter for this type of test facilities. Within the present paper a novel serration design wm be shown. The analyses as well as measurement results exhibit a clear improvement of the quiet zone field performance when compared to previous solutions. The new serration design was implemented and proved with the CCR 20/17 of Astrium GmbH at the Munich University of Applied Sciences.
An efficient algorithm for the RCS evaluation of the Monostatic Radar Cross Section (RCS) from a reduced set of bistatic near-field data is proposed. The algorithm allows to evaluate the monostatic RCS from near field data collected in an angular region centered on the direction of interest, whose amplitude depends on the size of the scatter and the distance of the measurement zone. Numerical examples on two dimensional elliptical cylinders show the effectiveness of the proposed technique.
Time domain processing (TDP) is used to analyze the quiet zone fields of antenna/RCS ranges. To carry out the time domain analysis, the quiet zone fields are probed over a band of frequencies. It is shown that TDP is a very effective tool for analyzing probe data. One can not only estimate the time and direction of arrival of various signals present in the quiet zone, but can also estimate their frequency dependence and quiet zone variations.
A method for implementing and/or improving background subtraction performance in wideband outdoor RCS range measurements is described. The method estimates and corrects for systematic changes that have occurred between a test and back ground measurement. Results from the application of a phase-only version of the techniques to background measurements from the RATSCAT RAMS facility are presented. Background subtraction performance improvements of as much as 20 dB are demonstrated.
RATSCAT has been heavily involved, as part of the DoD Range Certification Demonstration Program, in examining and documenting the underlying principles of all aspects of the outdoor measurement process. Our goal is to replace historical or "anecdotal" measurement approaches with processes founded on validated and documented procedures. This paper reports on the results of two areas of study. These are the effects on measurements caused by wind and calculation of target rotation rates. When RCS targets are measured outdoors on pylons or columns, some uncertainty will be introduced due to the effect of wind on the target and target support structure. This paper will present the results of an investigation into the errors introduced by wind motion on targets mounted on pylons or columns. When rotation rates are determined for target collection, the usual procedure is to employ a rule of thumb like "collecting three points per lobe" or "meeting the Nyquist criterion." This paper examines these common methods to determining rotation rates, and their impact on the measurement of the peak values of RCS magnitude and phase. Finally, the significance of these two measurement errors will be examined in light of their impact on outdoor range operations as well as on decisions based upon the collected RCS data.
Uncertainty analysis for fundamental standards is mature, but the cost overhead has, until recently, prevented much of this work being taken up by the UK RCS measurement community. The requirement to verify the radar signature of new equipment has made it necessary to examine in detail the RCS measurement process and to create a methodology for error budgeting. The paper reviews some basic concepts in estimating uncertainties, and describes work on 'squat' cylinder calibration standards that have been manufactured following designs proposed at previous AMTA conferences. The moment method code CLASP has provided the basic theoretical solutions which have been verified on a compact range through reference to a precise 100mm spherical standard. The concept of multiple standard calibrations is discussed, and recommendations are made for overall error budgeting and the intercomparison of range types.
An interlaboratory comparison is made between radar cross section (RCS) measurements at the test ranges at FOA Defence Research Establishment and SAAB Dynamics, Sweden. The comparison is made in order to increase the measurement and calibration quality at the ranges. An analysis of the deviations in the measured RCS data from the ranges provides a better understanding of the sources of errors. The RCS of two generic targets are measured at the X-band. The targets are simple airplane models, length and width are approximately 1.0 m, with no cavities. A brief comparison between some theoretical results and experimental RCS data are also presented.
The U.S. Navy has considerable experience in the radar cross section (RCS) measurement of dynamic targets. An understanding of the possible error sources and their relative magnitudes is critical to obtaining accurate and repeatable results. In addition to the usual potential sources of error in RCS measurements of stationary items, considerations with dynamic targets include target range and angle tracking, calibration, and various environmental effects. The primary considerations are identified and discussed, and an error budget is developed for a particular test scenario.
In order to assess the suitability of long thin metal rods as calibration devices for both co-polarized and cross-polarized (abbreviated as co-pol and x-pol) RCS measurements, we study RCS data from rods at broadside and compare them with 2D theoretical predictions. We find that the 45° tilt angle is optimum for calibration purposes. Near grazing incidence to a horizontal rod, the first traveling wave lobe in the HH pattern is a very prominent feature. Its angular location and amplitude have been measured as a function of frequency and compared with theory. A formerly unexplained error due to a contaminated calibration is identified.
The accurate measurement of Radar Cross Section (RCS) requires precise calibration "artifacts" as well as carefully executed measurement procedures. The Air Force Research Laboratory (AFRL) reviewed several existing common RCS calibration artifact standards and practices, and identified a number of improvements. Employing a modified "dual calibration" check procedure pioneered by AFRL, this paper demonstrates improved RCS calibration fidelity for a wide variety of static RCS calibration measurement applications. Our calibration results are verified through an industrial inter-laboratory (range) measurement program employing selected calibration artifact standards.
The purpose of this project was to determine the effects of fast neutron bombardment on the radar cross section of metal and dielectric spheres. The energetic neutrons interact with lattice atoms and, in the energy transfer that results, initiate a displacement cascade that effectiveiy damages the crystalline structure of the target material. The induced damage may change the RCS of the target via changes in the conductivity or relative permittivity. Theoretical lattice damage estimates are provided for fast neutron fluences of 1015 n/cm2 and 1016n/cm2. Limitations and potential improvement of damage estimates and measurements are also discussed.
A three-dimensional (3-D) imaging capability based on a linear FM measurement radar has been developed. This capability provides a means of resolving radar scattering centers in three dimensions, allowing the more accurate feature location and enabling the possibility of separating target returns from undesired environmental clutter. An existing portable radar cross section (RCS) measurement system was modified to incorporate a 3-D imaging capability. This modification allowed the system to remain highly portable and provide quick turnaround time with a typical measurement cycle comprising 20 minutes of data collection, followed by viewable 3D imagery within 5 minutes. The entire measurement system is comprised of a planar scanner and a single equipment rack. A 3-D RCS data set varies by frequency, azimuth, and elevation, and is obtained by scanning the radar antennas in azimuth and elevation. Innovative development of useful data visualization tools was one of the key efforts in this project. Visualization approaches include employing a mesh computer aided design (CAD) model aligned in 3-D space to the image data. The image is mapped to the surface of the model and the user can then move around the model to view it from any aspect in real time.
This paper presents an approximate, practical technique for the compensation of antenna pattern amplitude taper effects that occur in near field RCS data. The technique uses inverse synthetic aperture radar (ISAR) data sets. Complete pattern determination uses an iterative approach over target rotation angle and frequency bandwidth, with a series of near field ISAR images as input to obtain the corresponding corrected, near field, frequency/azimuth pattern data. Assumed is direct target illumination using a source with a known angular illumination pattern. The technique and its application environment in the Boeing Near Field Test Facility is described. It is then demonstrated using a near field data collection range of 100 feet from the target center of rotation. The approach is shown to be effective for target sizes with cross range extents extending to the one-way 3 dB points of the illumination taper (two-way 6 dB points). Demonstration of compensation performance and a study of accuracy achievable versus the near field image parameters used is presented.
A helicopter-based radar cross section (RCS) measurement system was designed and demonstrated during the past year. The system was a novel combination of modified and un-modified commercial off the shelf (COTS) equipment and software, a minor amount of new hardware, and extensive prior experience. Validation was accomplished using known calibration standards and existing test practices relevant to this type of system, and data were collected and processed for a number of targets of opportunity. The primary subsystems include the measurement radar, the helicopter, antennas and associated mount, boresighted video and recorder, and the calibration tools. The SCI1000 radar was employed because of the combination of its excellent performance at the desired test target range and its minimal physical and power demands. The Bell 500 helicopter was chosen for its size and its wide availability on the world market. Data products were RCS vs. aspect, downrange profile history, and two-dimensional imaging following pre-processing by a robust motion compensation algorithm.
RCS measurements at in service aircraft often require fast RCS - analysis capabilities. DaimlerChrysler Aerospace therefore extended its RaSigma facilities with a turntable and elevation system especially designed for RCS measurements at aircrafts. The designer and supplier of the turntable and elevation system was the German company HD GmbH. Aircraft with a maximum weight of 75 t can be raised to a height of approximately 13 m. The aircraft is supported by three girders at its landing gears or other hard points. The test range ist 300m long (today) and can increase up to 3000m . RCS measurement are performed in the gated CW mode. The RaSigma outdoor range operates in elevation range mode, with a special antenna design for a homogeneous field distribution over object height and frequency.
Compact range collimating reflectors provide far-field conditions for radar signature measurements. Traditionally, the quiet zone is presented uniformly about the collimator boresight and depends upon both the size of the reflector and the beamwidth of the illuminating antenna, with a maximum determined by the reflector dimensions. Targets are placed in the center of the quiet zone and rotated about the center of gravity (cg) during measurement. Limitations on target size are defined by the quiet zone bounds. For large targets with a non-central cg location, a portion of the target may extend beyond the quiet zone boundary. A technique for synthesizing a larger quiet zone uses displacement of the collimator beam by means of feed point offset to allow far-field measurement of an asymmetrically-mounted extended target. Simultaneous measurements for each offset are then combined to produce the complete measurement. This technique was implemented for measurements of an ARIES ballistic missile target.