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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.
The potential transmit power, and hence dynamic range of monostatic millimeter wave RCS measurements may be limited by the feed coupling of the antenna. Time domain gating can be used to reduce the measurement errors caused by this signal, as well as other undesired signals from scattering sources in the range, but does not protect the receiver from compression. Hardware gating can allow increases in transmit power by protecting the receiver from the effects of the feed coupling return. Unfortunately, equipment capable of hardware gating at millimeter wave frequencies is difficult to obtain. In addition, the usefulness of hardware gating is limited by the duty cycle loss in the measured signal. We describe a practical system using gating of the low frequency intermediate frequency (IF) signal in the receiver and a microwave pulse modulator prior to the millimeter wave multiplier in a mono-static millimeter wave RCS measurement system. We also describe methods to minimize the loss of measurement dynamic range due to duty cycle losses in this system. We demonstrate the use of this system for RCS measurements of simple targets, and compare the results with those obtained using software gating alone.
The UWB radar operates simultaneously over large bandwidth and the antenna parameters must refer to simultaneous performance over the whole of the bandwidth. Conventional frequency domain (FD) parameters like pattern, gain, etc. are not adequate for UWB antenna. This paper describes an UWB radar antenna planar near field (PNF) measurement system under construction to get the impulse response or transient characteristic of the UWB antenna. Unlike the conventional antenna or RCS time domain test system, the UWB radar signal instead of the carrier-free short time pulse was used to excite the antenna that can avoid the decrease of the dynamic range and satisfy the needs of SAR and the other UWB radar antennas measurement. In order to demonstrate the data analysis program, FDTD simulation software was used to calculate the E-field of M×N points in a fictitious plane at different times just like the actual oscilloscope’s sampling signals in the time domain planar near field (TDPNF) measurement. The calculated results can be considered the actual oscilloscope’s sampling output signals. Through non-direct frequency domain near field to far field transform and direct time domain near field to far field transform, we get the almost same radiation patterns comparing to the FD measurements and software simulation results. At last, varied time windows were used to remove the influences of the non-ideal measurement environment.
Hollow metallic aluminum spheres have been used for years for calibrating RCS measurement systems both indoors and outdoors. While many previous papers have identified the RCS calibration shortfalls associated with spheres [1,2], most of these papers have concentrated on indoor RCS measurement systems, where there exist a number of accurate calibration alternatives to spheres, including the so-called "squat cylinder" [3,4]. For outdoor free space RCS measurement systems, especially those designed to measure dynamically moving or changing targets, (i.e. the NASA Shuttle C-Band Debris Radar), calibration is a much tougher problem. Frequently, spheres are used to calibrate such systems, by releasing and tracking a sphere attached to a lighter-than-air balloon, or by tethering a sphere to a lighter-than -air balloon and allowing it to float through a fixed radar beam. Recently, the Air Force Research Laboratory Mobile Diagnostic Laboratory (MDL) had the opportunity to measure the clutter and uncertainty associated with balloon tethered Sphere RCS calibrations. Two spheres were measured suspended by various string types and a line under an 8 ft. diameter tethered Helium filled balloon. We will provide design guidance, signal processing techniques and measurement uncertainty to help minimize the clutter and error induced by balloon borne RCS calibration spheres.
Abstract. We present new RCS measurements from an 8-foot square flat plate for frequencies from 0.15 to 5.5 GHz. Guided by the theory, we study the peak RCS at normal incidence, the principal plane pattern, and the 3-dB beam-width in detail. The broadside echo from the plate is found to be extremely narrow at higher frequencies. From the errors, we estimate that the wave-field experienced by the plate is reasonably uniform to within +0.3 dB, over a wide dynamic range of 60 dB.
A large compact range facility required a foam column for RCS testing where the center of the quiet zone was six meters above the floor level. The RCS measurement after vector background subtraction, had to be accurate down to a –50 dBsm level from 1.5 GHz to 40 GHz. A foam column was constructed from a single billet of material. The foam column was evaluated as to its RCS level in both whole body and ISAR imaging modes. This paper describes the specification, construction and RCS evaluation of this column in the compact range facility. The column was evaluated at single frequencies and with RCS images from 2 GHz to 36 GHz using a gated CW radar. Data is presented that shows the effects of the column on the response of a calibration sphere and the response of the column itself. A study of the foam column imaging response used as the background for vector background subtraction is also described. Targets in the –60 dBsm range were successfully imaged with vector background subtraction of the foam column.