Total Radar Cross Section Research Articles

A Comparison of Numerically Modelled Iceberg Backscatter Signatures with Sentinel-1 C-Band Synthetic Aperture Radar Acquisitions

Use of machine learning to develop algorithms for distinguishing iceberg and vessel targets requires large validated data sets that are often costly, time consuming and, in some cases, inaccessible. Generating electromagnetic (EM) backscatter models of iceberg and ship targets can be a vital step in developing a robust iceberg/ship classification algorithm. In this work, EM backscatter models for icebergs are developed using an EM backscatter modelling tool called GRECOSAR and compared with ground truth data. The imaging scene consists of iceberg targets surrounded by the ocean surface. The 3D computer aided design models of the icebergs were obtained using LiDAR and multi-beam sonar data collected during a field program off the coast of Salvage, Newfoundland and Labrador, Canada. While profiling the iceberg targets, a synthetic aperture radar (SAR) image from Sentinel-1A was captured and compared with the simulated SAR images. Comparisons made in terms of total radar cross section (TRCS) and the SAR signature of the targets generally indicate credible simulations. Simulated SAR images were generated at low and high dielectric conditions to mimic cold and melt iceberg surfaces. Variability of the TRCS and morphology as a function of target orientation highlights the usefulness of EM modelling in developing robust iceberg/ship classifiers.

Using a second-order bistatic cross-section of the ocean surface for bistatic shipborne HFSWR

ABSTRACTThe second-order radar cross section (RCS) of ocean surface is analytically derived for the case in which the radar transmitter is located inland and the receiving antenna is mounted on a shipborne platform. With our previously derived first-order RCS result, the total RCS of ocean surface is simulated for a variety of radar operating parameters and sea states. According to simulation results, it is seen that the relative effect on the second-order spectra due to the platform motion is much smaller than that on the first-order. For the conditions of the radar working with a high operating frequency or a high sea state, the increase of the second-order spectral energy may contaminate the first-order component severely. The obtained results may be useful for setting appropriate limits on the use of radar operating parameters or the bistatic site geometries, from which condition the ocean surface parameters can be effectively extracted from the radar data.

Target sequence optimization for multiple debris rendezvous using low thrust based on characteristics of SSO

A method is proposed to select the target sequence for a J 2-perturbed multiple debris rendezvous mission aimed at removing dozens of debris from several thousand debris candidates running on sun-synchronous orbits (SSO). The solving methodology proceeds in two steps: Firstly, the variance of the right ascension of ascending node (RAAN) of the debris group is used for narrowing down the potential debris candidate; secondly, the debris of the candidate group that has closest RAAN to the current debris is chosen as the next debris. The low thrust near-minimum-fuel trajectories of each rendezvous leg are obtained by the indirect optimization method. The proposed approach is demonstrated for the problem of the 8th China Trajectory Optimization Competition (CTOC). The radar cross section (RCS) of the debris is also considered in the first step since the primary performance index of the competition is to maximize the total RCS of the debris visited. The results show that the proposed approach achieves better performance within a competition period. Of the many rendezvous sequences found, the best one submitted for the competition obtained a total RCS of 184 by accomplishing rendezvous with 70 debris within a transfer duration of one year.

On the Influence of Scattering From Traffic Signs in Vehicle-to-X Communications

As an important scatterer in vehicle-to-X (V2X) communication scenarios, traffic signs frequently appear along roads and can affect the propagation channel appreciably. Although traffic signs can be considered as an important part in such scattering scenarios, knowledge of their bistatic radar cross section (RCS) is still absent. This paper presents an integration of the analytical models, full-wave simulation, measurement, and validation of the bistatic RCS of three types of representative traffic signs for V2X communication. First, the total RCS of the traffic signs is calculated by summing up the field contributions of the individual parts with their own phase relationships. Furthermore, simulations using full-wave analysis are performed to validate the analytical models for RCSs in the far field under plane-wave illumination. Since the high-frequency calculation techniques used here are applicable only under plane-wave excitation, the traffic-sign parts are divided into small elements, where this precondition is locally valid. Measurements are conducted in an open-area test site at the National Metrology Institute of Germany to validate the model in the near field (spherical wave from a point source). Corresponding comparisons show that the method of decomposing the traffic sign into small parts supports an effective way to embed the analytical models into ray-tracing tools, thus improving propagation modeling in V2X communication.

RECONFIGURABLE RADAR ABSORBING STRUCTURE APPLIED TO THE ANTENNA RADAR CROSS SECTION REDUCTION

An active reconfigurable radar absorbing structure (RAS) with the pin diode was proposed to reduce the radar cross section (RCS) of antenna. The operating states of the RAS reflector can be switched by using the pin diode. For ON-state and OFF-state diodes, the reflection coefficients of the RAS reflector were less than −25 dB and more than −0.8 dB around 8.3 GHz, respectively. The RAS reflector with ON-state diodes can be used as a dipole antenna reflector and has the same radiation performance as a dipole with a metal reflector, while the RAS reflector with OFF-state diodes can be used as a radar absorber for RCS reduction. Meanwhile, chessboard-like geometry RAS reflector was proposed to achieve wideband RCS reduction. The RCS reduction band covers the working band and is extended to 5-18 GHz. The results show that the reconfigurable RAS reflector can contribute to the antenna RCS reduction at working frequency without loss of radiation performance of dipole antenna. With the detection and stealth technology developing rapidly, radar cross section (RCS) reduction (1-4) has been a serious problem in military applications and has attracted significant attention recently. Since the scattering of the antennas has contributed a lot to the total RCS for low observable platforms, more and more attention has been paid to antenna scattering. Shaping, coating with radar absorbing materials (RAM) and using passive and active cancellation technology are basic methods in stealth technology (5-7). Furthermore, a number of new structures and materials are applied to the RCS reduction of antenna, such as artificial magnetic conductor (AMC), radar absorbing structure (RAS), frequency selective surface (FSS), etc. (8-11). However, these structures and materials cannot be used for stealth in the working band. When RAS is used, the gain of the antenna has a large degeneration (12), and the application of AMC will increase the profile of the antenna. All of them greatly deteriorate the stealth performance and application of radar system or other platform. In early years, antennas did not need to work in airborne or missile borne systems continuously. To realize the stealth of antenna, the radar was opened in close proximity to the target and shut down through the dangerous area. This method has the advantages of simple, feasible, and good stealth characteristic. In addition, the radiation performance of the antenna is preserved. However, this method can only reduce the antenna mode scattering, and the structural mode scattering still exists. Meanwhile, general metamaterials are completely passive structures, and the properties of these metamaterials cannot be changed. Therefore, in the complex electromagnetic environment, these metamaterials cannot be able to quickly adapt to the changes in the external electromagnetic environment and reduce its effect. In order to overcome these problems, reconfigurable RAS is put forward as a new concept. Reconfigurable technology has been successfully applied to antenna design. Early research focused on changing the current distribution by adjusting the radiator structure, which made the frequency, pattern, polarization or impedance of antenna changed. Currently, the reconfigurable metamaterial is

A novel stealth Vivaldi antenna with low radar cross section

A novel stealth Vivaldi antenna with low radar cross section (RCS) is proposed in this article that covers the ultrawide band (UWB) from 2 to 12 GHz. As a special scatterer, the antenna can be responsible for the larger part of the total RCS of many military platforms. In this article, the configuration of the metal patch is modified, based on the difference of the current distribution while the antenna radiates and scatters. The monostatic radar cross section of proposed antenna is reduced in most parts of the band with polarized and polarized. Maximally 14 dBsm RCS reduction is achieved. The gain of the proposed antenna and reference antenna are in good agreement in most of the impedance bandwidth. Results are provided to demonstrate that the excellent radiation and perfect stealth performance is achieved. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:255–261, 2015.

Scattering suppression and wideband tunability of a flexible mantle cloak for finite-length conducting rods

A simple, thin, flexible mantle cloak for conducting rods based on scattering cancellation is analyzed, designed and experimentally realized. We show strong scattering suppression at all angles of incidence, for both far-field plane-wave and near-field Gaussian excitations. The required effective shunt surface impedance is realized by a subwavelength patch array, targeting the suppression of the dominant omnidirectional scattering contribution of a conductive rod. Full-wave simulations predict a total radar cross-section reduction better than 14 dB in the lossless case and nearly 8 dB when considering a lossy substrate in the cover. Measurements of the realized cloak are consistent and validate these numerical predictions. The proposed geometry is also shown to be an ideal platform for monolithic integration of varactor diodes, allowing real-time tuning of the effective surface capacitance of the cloak. We show with numerical simulations the possibility of tunable scattering suppression over 1 GHz of bandwidth by seamlessly integrating varactor diodes in our mantle cloak design.

Scattering Analysis of a Compact Dipole Array with Series and Parallel Feed Network including Mutual Coupling Effect

The current focus in defense arena is towards the stealth technology with an emphasis to control the radar cross-section (RCS). The scattering from the antennas mounted over the platform is of prime importance especially for a low-observable aerospace vehicle. This paper presents the analysis of the scattering cross section of a uniformly spaced linear dipole array. Two types of feed networks, that is, series and parallel feed networks, are considered. The total RCS of phased array with either kind of feed network is obtained by following the signal as it enters through the aperture and travels through the feed network. The RCS estimation of array is done including the mutual coupling effect between the dipole elements in three configurations, that is, side-by-side, collinear, and parallel-in-echelon. The results presented can be useful while designing a phased array with optimum performance towards low observability.

Anisotropic Transmission-Line Metamaterials for 2-D Transformation Optics Applications

In this contribution, we present a two-dimensional metamaterial unit cell which synthesizes effective material parameters needed for “transformation optics” applications. The metamaterial consists of a grid of reactively loaded transmission-line segments and is a generalization of a previously presented unit cell in that it also synthesizes off-diagonal elements of the permeability tensor. We apply this unit cell to two “transformation optics” applications, a retro-directive reflector, and a cloak. This cloak is different from the so-far reported split-ring-resonator/wire structures in that it not only synthesizes the required μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ρ</sub> and ε <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> distribution but also the μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">φ</sub> one. For the cloak, detailed radar cross-section (RCS) and bandwidth results are presented. It is shown that the total RCS bandwidth is 33.5%, and that losses influence the cloaking performance not critically, pointing to the possibility of practical “transformation optics” designs using the proposed unit cell. Full-wave simulation results of a transmission-line metamaterial cloak in microstrip technology are presented, verifying that the unit cell presented in this paper synthesizes the effective material parameters needed for “transformation optics” or applications that require effective material parameters with off-diagonal tensor elements.

Measurements of the Effect of Rain-Induced Sea Surface Roughness on the QuikSCAT Scatterometer Radar Cross Section

Radar measurements of the sea surface, with satellite scatterometers that operate at Ku-band, are affected by the presence of rain through modification of the sea surface roughness by rain impacts. This is in addition to wind driven roughness, atmospheric scattering, and attenuation that affect the measured normalized radar cross section (NRCS). This paper presents a case study of the increase of the total radar cross section, averaged across surface illuminated areas (individual footprints) of the SeaWinds scatterometer (on QuikSCAT) caused by rain striking the sea surface. This effort combines satellite-based Ku-band data with high-resolution 3-D volumetric rain measurements, from simultaneous collocated Next Generation Weather Radar data. The results to be presented were acquired during a significant rain event in the Gulf of Mexico, to the east of Corpus Christi, and just south of Houston, TX, in May 2005. The results of this paper show dependence on wind speed, rainrate, and polarization. They agree with numerous surface-based studies (single point measurements), using ocean platforms and wind-wave tanks, whose data were collected under similar conditions. For example, at rainrates less than 10 mm/hr, the relative change in surface roughness is seen to decrease as the wind magnitude increases from 5 to 7 m/s. Another consistent observation is that the vertical polarization NRCS shows less sensitivity to rainrate than does horizontal.

Automated design of threats and shields under hypervelocity impacts by using successive optimization methodology

In this study, predictive hydrocode simulations are coupled with approximate optimization (AO) methodology to achieve successive design automation for a projectile-Whipple shield (WS) system at hypervelocity impact (HVI) conditions. Successive design methodology is first applied to find the most dangerous threat for a given WS design by varying the shape and orientation of a projectile while imposing constraints on the total projectile mass and radar cross section (RCS). Subsequent optimization procedure is then carried on to improve the baseline WS design parameters. A parametric multi-layered stuffed WS model is considered with varying thicknesses of each layer and variable positions of the inter-layers while having a constraint on the areal density. HVI simulations are conducted by using a non-linear explicit dynamics numerical solver, LS-DYNA. Coupled finite element and smoothed particle hydrodynamics (SPH) parametric models are developed for the predictive numerical simulations. LS-OPT is employed to implement the design optimization process based on response surface methodology. It is found that the ideal spherical projectiles are not necessarily presenting the most dangerous threat compared to the ones with irregular shapes and random orientations, which have the same mass and RCS. Therefore, projectiles with different shapes and orientations should be considered while designing a WS. It is also shown that, successive AO methodology coupled with predictive hydrocode simulations can easily be utilized to enhance WS design.

Template-Based Target Identification and Confusion Matrices [AESS Tutorial IV

One-dimensional high-range-resolution (HRR) and two-dimensional range-Doppler-imaging (RDI) radar represent possible sensor technologies where template-based techniques can be applied to perform combat identification (CID). The majority of the research reported in these areas consists of empirical studies. This article provides a theoretical basis for understanding some of the fundamental trade-offs associated with these CID techniques, such as the following: What are the relative advantages of RDI over HRR radar or of finer versus coarser resolution in the HRR process? What is the relative advantage of coherent over noncoherent processing? How do target correlations, signal-to-noise ratio (SNR), and target scintillation affect the ability to identify targets? Because confusion matrices are often used to characterize the performance of CID systems, we provide analytical methods for calculating the entries in confusion matrices as a function of the issues cited above. These formulations provide analytical bases to guide system trade-off decisions. The organization of this paper is as follows. We begin with a short overview of HRR and RDI and then explore a number of ways to process the associated target templates that range from an ideal, theoretical approach to an approach that would be more feasible to implement within current-day radars. We first develop analytic template-based methodologies for constructing confusion matrix entries for nonscintillating targets for both coherent and noncoherent processing assumptions. The confusion matrix entries in these cases are conditional probabilities obtained from a simple rule: find the probability that among m (in general, correlated) random variables, each associated with a possible target, that any one is the largest. For the noncoherent case, the successful application of this rule requires the target template values to explicitly include the effects of thermal noise (noise-adjusted templates). We conclude by showing how to calculate theoretically optimum results (e.g., using maximum likelihood techniques) for noncoherent processing of targets that exhibit uncorrelated Swerling 1 scintillation in ail resolution bins as a function of the SNR. This approach allows us to include overall target intensity (e.g., total radar cross section (RCS)) as a further factor in the target decision process.

Improvements of Edges Diffraction Computing in GRECO

Graphical Electromagnetic Computing (GRECO) is one of the valuable methods for computing the radar cross section (RCS) of complex radar target in high frequency region. But there are some shortages of wedge detecting method in the original GRECO literature. A new method for collecting the edge pixels and wedge parameters is presented in this paper. An expression of edge diffraction field in the original GRECO literature is in error, the error-corrected formulas are derived by using method of equivalent edge currents (MEC) and physical theory of diffraction (PTD). Finally, the total RCS expression is given by physical optics (PO) and PTD method. The computing results are in close agreement with the measured data.

A Scheme for Analyzing the RCS of a Scale Model Beyond the Size Measureable in the Range of Millimeter-Wave

The problem of obtaining the radar cross section (RCS) of a scale model too large to measure in the range of millimeter-wave by measurement is investigated. This topic, to the best of our knowledge, has been little investigated due to its complexity. A scheme named RCS part measurement and synthesis to this problem is developed in this paper. This method combines measurement with theoretical calculation. The first step in using the method is that a scale model is partitioned into several parts measurable. Then the contributions of the sections and shadow region shadowed by all other parts are removed from the measured RCS data of every part. Finally, the scattered fields of all the parts are synthesized to obtain the total RCS of the scale model by means of the technique of relative phase synthesis. A result is presented to illustrate the utility of this scheme.

Plane-wave scattering by strip-loaded circular dielectric cylinders in the case of oblique incidence and arbitrary polarization

Plane-wave scattering by strip-loaded circular, multilayered dielectric cylinders is investigated in the most general case of oblique incidence and arbitrary polarization. The problem is formulated via systems of singular integral-integrodifferential equations of the first kind which are most efficiently discretized on the basis of previously developed analytical algorithms. Several internal tests along with extended comparisons with available results have been completed to validate the numerical codes. Plotted results for both the induced surface current densities and the total radar cross section reveal how the scattering properties may be controlled by changing several physical and geometrical parameters of the structure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theoretical and Experimental Determination of the Polarimetric Antenna Radar Cross Section

ABSTRACT The total radar cross section (RCS) of antennas is the vector sum of structural and antenna mode scattering. These RCS contributions can be described completely by their polarimetric scattering matrices. The paper introduces a new polarimetric network description for three and four port antennas. The total scattering matrix is separated into the individual contributions with a new measurement procedure, based on complex load variations. Two waveguide and two planar antennas are chosen for demonstration and verification. By load variation the antenna mode scattering can be manipulated in phase and amplitude. It can especially be steered to compensate for the structural and aperture contributions. The possibilities for RCS minimization under polarimetric aspects are shown to be limited in bandwidth, polarization and aspect angle.

An experimental study of microwave scattering from rain- and wind-roughened seas

This paper investigates radar cross-section (RCS) characteristics of rain- and wind-roughened sea-surfaces. We conducted experiments in laboratory wind-wave tanks using artificial rain. The study includes light rain rates, light wind speeds, and combinations of these. A 36 Ghz scatterometer was operated at 30 deg incidence angle and with vertical polarization. RCS data were obtained not only with the scatterometer pointing up-wind but also as a function of azimuthal angle. We use a scatterometer rain and wind model SRWM-1, which relates the total average RCS in storms to the sum of the average RCS due to rain plus the average RCS due to wind. Implications of the study for operational monitoring of wind in rainy oceanic areas by satellite-borne instruments is discussed.

Effects of sea maturity on satellite altimeter measurements

For equilibrium arid near‐equilibrium sea states, the wave slope variance is a function of wind speed U and of the sea maturity. The influence of both factors on the altimeter measurements of wind speed, wave height, and radar cross section σ0 is studied experimentally. The necessary theoretical background, both on wave statistics and on the near‐nadir radar backscatter, is outlined. It is based on a recently proposed view that the effective fractal dimension for a surface patch corresponding to the equilibrium range of wave spectra increases as the wave field matures. The experimental part is based on 1 year's worth of Geosat altimeter observations colocated with in situ wind and wave measurements by 20 NOAA buoys. Errors and biases in altimeter wind speed and wave height measurements are investigated. A geophysically significant error trend correlated with the sea maturity (i.e., with C0/U, where C0 is the phase velocity of waves corresponding to the spectral peak and U is the mean wind speed well above the surface) is found in wind speed measurements. This trend is explained by examining the effect of the generalized wind fetch, , on the curves of the observed dependence σ0 = f(U, X). We conclude, in particular, that unambiguous measurements of wind speed by altimeter, in a wide range of sea states, are impossible without accounting for the actual degree of wave development. An approach to a more accurate retrieval of wind speeds is suggested as based on accounting for the actual degree of wave development, which can be achieved through processing the total radar cross section simultaneously with the significant wave height information contained in altimeter waveforms. The potential capability of a satellite altimeter to estimate wave age and similar measures of wind‐wave coupling is discussed. This capability expands the use of satellite altimeters for air‐sea interaction studies.

Aerodynamics and radar signature - A combination of theoretical methods

Combat aircraft are threatened by radar-controlled anti-aircraft systems. Knowledge of the scattering of electromagnetic waves from aircraft allows aerodynamic designers to design a low radar signature or to improve the tactics of aircraft in service to successfully avoid enemy defensive reaction. A theoretical approach is presented to estimate the radar signatures of complex aircraft configurations including external stores. The signature is evaluated by determining the radar cross sections of intended radar-observation directions. The radar cross section of a certain aspect view of a radar observation is evaluated by combining specular geometrical and physical optics for curved-surface elements, such as wing surfaces, that are large with respect to the radar's wavelength. Diffraction formulas are added to introduce the radar-reflection characteristics of edges. The geometric input is equal to the buildup of usual aerodynamic panel methods and, by the evaluation of the panels' principal curvatures by higher-order means, allows the regard of the curved aircraft surfaces. The diffractions typical for edges (wing edges, etc.) are included with regard to the edges' sharpness and geometric shape. The total radar cross section is determined by summing up all reflecting areas (by the combination of the contributing panels) and edge elements. Thus, an aerodynamic surface discretization can be used without modification. The signatures of principal bodies and a fighter aircraft, both armed and unarmed, when exposed to a typical radar illumination, are presented.

A radar study of Comet IRAS-Araki-Alcock 1983d

Radar echoes from Comet IRAS-Araki-Alcock at wavelengths 3.54 and 12.9 cm indicate that the comet's nucleus is very rough on a scale larger than the radar wavelengths; however, the low polarization ratio (25 percent at 3.54 cm) indicates that the scattering is not dominated by multiple reflections, internal reflections, or large abundances of sharp edges, cracks, and pits. The shape of the nucleus probably departs greatly from a sphere with average radii near 3-4 km. The nucleus does not appear to look significantly different from a number of Apollo and Amor asteroids except that: (1) there is a suggestion that minor structure moves rapidly across the spectra, and (2) the debris not gravitationally bound to the comet was detected, and contributes 25 percent of the total radar cross section at the 12.9-cm wavelength. Other considerations suggest that the pole was at least 45 deg away from the line of sight on two days of observation, and that the rotation period is approximately 1-2 days.