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The National Radar Cross Section Measurement Facilities Certification Program seeks to raise collectively the quality bar across the community. A program to accomplish this goal was initiated in 1995. It continues with facilities joining the program every year. The program has now entered the recertification phase for facilities that achieved certification five or more years ago. This paper will briefly cover the history of the program, the participants, the certification process and criteria, the recertification process, status, and the way ahead.
A real-time S-band radar imaging system will be shown in this paper that uses a spatially diverse antenna array connected to a highly sensitive linear FM radar system and uses a synthetic aperture radar (SAR) imaging algorithm to produce real-time radar imagery. The core of this radar system is a high-sensitivity, range gated, radar architecture. Previous work has demonstrated the effectiveness of this radar architecture for applications requiring low-power and high sensitivity for imaging through lossy dielectric slabs at S-band and in free space at both S and X bands. From these results it was decided to develop a real-time S-band SAR imaging system. This is achieved by constructing a spatially diverse antenna array that plugs directly into a pair of S-band transmit and receive radar front ends; thereby providing the ability for real-time SAR imaging of objects. The radar system chirps from approximately 2 GHz to 4 GHz at various rates from 700 microseconds to 10 milliseconds. Transmit power is adjustable from approximately 1 milliwatt or less. The image update rate is approximately one image every 1.9 seconds when operating at a chirp rate of 2.5 milliseconds. This system is capable of producing imagery of target scenes made up of objects as small as 1.25 inch tall nails in free space without the use of coherent integration. Previous applications for this radar system include imaging through dielectric slabs. It will be shown in this paper that this radar system could also be useful for real-time radar imaging of low RCS targets at S-band.
This paper deals with characterization of passive ultra-high frequency (UHF) radio frequency identification (RFID) tag performance. Tag’s energy harvesting properties and the significance of the backscattered signal strength and radar cross section (RCS) of the tag are discussed using two examples: dipole tag antennas of various widths and identification of industrial paper reels.
Commercial windmill driven power turbines (“Wind Turbines”) are expanding in popularity and use in the commercial power industry since they can generate significant electricity without using fuel or emitting carbon dioxide “greenhouse gas”. In-country and near-off shore wind turbines are becoming more common on the European continent, and the United States has recently set long term goals to generate 10% of national electric power using renewable sources. In order to make such turbines efficient, current 1.5 MW wind turbine towers and rotors are very large, with blades exceeding 67 meters in diameter, and tower heights exceeding 55 meters. Newer 4.5 MW designs are expected to be even larger. The problem with such large, moving metallic devices is the potential interference such structures present to an array of civilian air traffic control radars. A recent study by the Undersecretary of Defense for Space and Sensor Technology acknowledged the potential performance impact wind turbines introduce when sited within line of site of air traffic control or air route radars. [1]. In the Spring of 2006, the Air Force Research Laboratory embarked on a rigorous measurement and prediction program to provide credible data to national decision makers on the magnitude of the signatures, so the interference issues could be credibly studied. This paper, the first of two parts, will discuss the calibrated RCS measurement of the turbines and compare this data (with uncertainty) to modeled data.
The DGA/CELAR (France) (Centre d'Electronique de l'Armement: French Center for Armament Electronics) is able to measure targets in order to get their RCS (Radar Cross Section). Yet CELAR RCS measurement facilities are not compact bases and therefore the measured field is a near field. This article proposes a solution allowing the transformation of this near field to a far field and this in the three dimensions of space without limiting any dimension with Fraunhöfer criterion. Thanks to this method the RCS of a target is able to be known in any direction of space and moreover the calculation of a three-dimensional ISAR (Inverse Synthetic Aperture Radar) picture is thus possible. At first the theoretic part of our work is presented. Then a fast method in order to calculate the transformation of a near field to a far field by optimising the calculation time thanks to signal processing theory is given. Finally obtained results from simulated bright points are presented.
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed at CEA for indoor near field monostatic RCS assessment. The experimental layout is composed of a motorized rotating arch (horizontal axis) holding the measurement antennas. The target is located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allows full 3D near field monostatic RCS characterization. Two bipolarization monostatic RF transmitting and receiving antennas are driven by a fast network analyser : - an optimised phased array antenna for frequencies from 800 MHz to 1.8 GHz - a wide band standard gain horn from 2 GHz to 12 GHz. This paper describes the experimental layout and the numerical post processing computation of the raw RCS data. Calibrated RCS results of a canonical target are also presented and the comparison with compact range RCS measurements is detailed.
The DGA/CELAR (France) (Centre d'Electronique de l'Armement: French Center for Armament Electronics) is able to measure targets in order to get their RCS (Radar Cross Section). Once this RCS is acquired it may be very interesting to calculate RADAR pictures of these targets because RADAR picture allows emphasizing the bright points. Until now, CELAR produced images in two dimensions, but these pictures have shown their limits in order to locate problems in altitude. This article fills this gap while proposing two methods in order to get an image in three dimensions: a method using a three-dimensional Fourier transform and a method based on interferometry.
The 2004 AMTA paper entitled “The “Cam” RCS Dual-Cal Standard” introduced the theoretical concept of the “cam,” a new calibration standard geometry for use in a static RCS measurement system that could simultaneously offer multiple “exact” RCS values based on simple azimuth rotation of the object. Since that publication, we have constructed a “cam” to further explore its utility. The device was fabricated to strict tolerances and its as-built physical geometry meticulously measured. Utilizing these characteristics and moment-method analysis, a high-accuracy computational electromagnetic (CEM) “exact” file required for calibration was produced. Finally, the “cam” was evaluated for its efficacy as a single device that could be utilized as a dual-cal standard. This development was conducted with a particular focus on the hypothesized improvements offered by the new standard, such as the elimination of frequency nulls exhibited by other resonant-sized calibration devices, and improved operational efficiency. In this follow-on paper, we present the advantages to and challenges involved in making the “cam” a viable RCS dual-cal standard by describing the fabrication, modeling and performance characterization.
ACC has developed for the ESA-ESTEC CATR a compact but highly versatile 5-axis positioner. It is composed of a roll axis, upper azimuth, elevation, translation and lower azimuth axis. The clearance between the floor and the translation stage is designed to pass over a 12” walkway absorber while the roll axis height is only 155 cm (~5 feet). The standard configuration for medium or high gain antennas is the roll-over-azimuth or elevation-overazimuth configuration with a vertical interface for the AUT. For omni-directional antennas and RCS measurements, the positioner can be configured as a low profile azimuth positioner with a horizontal interface without a blocking structure behind the AUT. The positioner can also be configured for bistatic RCS measurements and Spherical Near Field. With the addition of a linear scanner, the Quiet Zone can be scanned in a polar way but also planar scanning is possible. Other key parameters are: angular accuracy: 0.01°, accuracy of the translation axis: 0.01 mm, load capacity 100 kg.
The Microwaves and Radar Institute regularly performs calibration campaigns for spaceborne synthetic aperture radar (SAR) systems, among which have been X-SAR, SRTM, and ASAR. Tight performance specifications for future spaceborne SAR systems like TerraSAR-X and TanDEM-X demand an absolute radiometric accuracy of better than 1 dB. The relative and absolute radiometric calibration of SAR systems depends on reference point targets (i. e. passive corner reflectors and active transponders), which are deployed on ground, with precisely known radar cross section (RCS). An outdoor far-field RCS measurement facility has been designed and an experimental test range has been implemented in Oberpfaffenhofen to precisely measure the RCS of reference targets used in future X-band SAR calibration campaigns. Special attention has been given to the fact that the active calibration targets should be measured under the most realistic conditions, i. e. utilizing chirp impulses (bandwidth up to 500 MHz, pulse duration of 2 µs for a 300 m test range). Tests have been performed to characterize the test range parameters. They include transmit/receive decoupling, background estimation, and two different amplitude calibrations: both direct (calibration with accurately known reference target) and indirect (based on the radar range equation and individual characteristics). Based on an uncertainty analysis, a good agreement between both methods could be found. In this paper, the design details of the RCS measurement facility and the characterizing tests including amplitude calibration will be presented.
The dynamic range of a measurement system is typically evaluated in the frequency domain. However, for radar-cross-section (RCS) measurements, time processing of the frequency-domain data is often utilized to determine the temporal or spatial (down-range) location of responses. Dynamic range in the time domain is thus of considerable importance in determining what range of responses can be resolved and identified. While the coherent integration inherent in the pulse-compression process can increase the time-domain dynamic range beyond that of the frequency-domain, non-linearity in the measurement system leads to signal-dependent noise which, in turn, limits the time-domain dynamic range to a much smaller value. Thus, specification and characterization of time-domain dynamic range is critical for understanding the linearity requirements and the time-domain capability of the measurement system. This paper reviews design considerations, error sources, and measurement methods relevant to optimizing dynamic range in the time domain. Examples of time-domain measurements are included.
Method of moments (MoM) codes have become have become increasingly capable and accurate for predicting the radiation and scattering from structures with dimensions up to several tens of wavelengths. In particular, for simple structures like canonical shapes or antenna / RCS test fixtures, especially those with material treatments, the primary source of disagreement between measurements and predictions is often due to differences between the “as-designed” and “as-built” material parameters rather than to the underlying MoM code itself. This paper describes an algorithm that uses a MoM model combined with backscatter measurements to estimate the “as-built” materials parameters for the case where the treatments can be modeled using an equivalent boundary condition. The algorithm is a variant of the network model technique described in [1]-[3]. The paper presents a brief formulation of the network model materials characterization algorithm, along with numerical simulations of its performance for a simple canonical RCS shape using the CARLOS-3D™ MoM code [4]. The convergence properties of the algorithm are also discussed.
While using squat cylinders for calibrations, we study the MoM-simulated data in terms of surface waves. We have found that the fine structures in both the amplitude and the phase are related to the target geometry. Key Words: RCS calibration, simulation, polarization
Techniques for measuring the radar cross section (RCS) of a target in a controlled environment are well known and established and many commercial systems are available for making these measurements. However, when RCS measurements need to be taken in a variable environment – such as over the ocean – several important issues are introduced that need to be carefully considered before a meaningful measurement can be made. This paper shall discuss some of these issues and present a measurement approach that appears to reduce the uncertainty that these factors introduce.
This paper discusses the Blue Airborne Target Signatures (BATS) database. BATS is the United States Air Force central repository for US and allied signature data. It resides at and is maintained by the Signatures Element, 453rd Electronic Warfare Squadron, Air Force Information Warfare Center, Lackland AFB TX. BATS contains radar cross section (RCS), infrared (IR), and antenna pattern (AP) data, both measured and simulated. The history and background of BATS is also presented, as well as current activities.
This paper describes the motivation and major issues related to the design of an RCS radar instrumentation system for use in a compact range. The high degree of sophistication implemented in commercially-available radar systems renders them subject to significant MTTR (mean time to repair) with corresponding losses in range productivity. The objective of the design effort was to develop a system of minimal complexity, maximally suited to troubleshooting and repair by laboratory personnel, while retaining the operational efficiency normally provided by the commercial systems.
This paper proposes an approach for the wireless industry to use in assessing its measurement facilities to help ensure that they are providing measurement results that are accurate and repeatable, with a knowable error and uncertainty. This approach is based upon the successful development of a certification program for US RCS facilities based upon an ISO 17025-like standard. Key pieces of this program include a documentation standard for defining the facility's capabilities and operation, and a Report of Measurement and an accompanying Uncertainty Analysis. This paper will discuss the similarities and differences between an existing RCS certification program and the proposed wireless program, to include technical distinctions between the two programs. These distinctions are based upon such factors as a 1-way instead of 2-way propagation paths, the various modulation schemes in use today and the different types of measurements such as Specific Absorption Rate that are not considered in RCS measurements.
CEA-Cesta has developed a new phased array antenna for RCS dual polarization wide bandwidth measurement in V/UHF bands. This array enables us to enhance signal to noise ratio especially at low frequencies. It is composed of 3 sub arrays dedicated each to one frequency band. The innovative design allows installing it in one of CEA/CESTA RCS facilities called “CAMELIA”. In order to validate this array in the highest sub-band [700 to 2000MHz], we measured in both HH and VV polarizations the near field RCS of a 2.5m long NASA almond target. This canonical object has been made of polystyrene coated with conducting nickel varnish. It has been hung on an eight wires rotating positionner. The results are compared with the data acquired in a classical RCS compact range and with the output of the 3D finite element code called ODYSSEE developed at CEA.
It is widely known to radar engineers that the best radar receiver is a correlation receiver, which correlates the originally transmitted radar pulse with received pulses from the reflection. But the true correlation receiver could not yet be realized in past. The advancement of fiber optical technology changes that. The new and true correlation receiver, which has been referred to as interferoceiver, revolutionizes the technical foundation of radar and electronic warfare. The present talk discusses the use of the interferoceiver in advancing techniques of RCS measurement and RF imaging.
For many years now, General Dynamics has described the development, characterization, and performance of an image-based circular near-field-to-far-field transformation (CNFFFT) for predicting far-field radar cross-section (RCS) from near-field measurements collected on a circular path around the target. In this paper, we consider the CNFFFT algorithm as an azimuthal filtering process and develop a formulation capable of transforming data that is not measured over a full 360º. Such a formulation has applications in measurement scenarios where collection of a complete rotation is not practical. As part of the development, we provide guidelines for the near-field data support required to achieve a desired accuracy in the sub-360º CNFFFT result. Numerical simulations are provided to demonstrate that the results of this partial-rotation formulation are consistent with the full-circle CNFFFT results presented in past papers.