Bistatic Radar Cross Section Research Articles

The Closed-Form Expressions for the Bistatic Quantum Radar Cross Section of the Typical Simple Plates

Closed-form expressions for the bistatic quantum radar scattered by the circular and triangular plates with the single-photon incidence are derived in the field of the Fourier relationship between the surface atom distribution and the bistatic quantum radar cross section (BIQRCS). The proposed expressions are highly efficient useful tools to analytically estimate the BIQRCS of the typical simple plates in the condition of high frequency approximation. And the formulas have been preliminarily verified by the numerical solution for the typical incident angles. In addition, the analysis of the quantum effect of sidelobes of BIQRCS in scattering, which can be seen as a kind of quantum interference, is also presented. We expect that this achievement will apply to the modeling of bistatic quantum radar scattering.

Bistatic High-Frequency Radar Cross-Section of the Ocean Surface with Arbitrary Wave Heights

The scattering theory developed in the past decades for high-frequency radio oceanography has been restricted to surfaces with small heights and small slopes. In the present work, the scattering theory for bistatic high-frequency radars is extended to ocean surfaces with arbitrary wave heights. Based on recent theoretical developments in the scattering theory for ocean surfaces with arbitrary heights for monostatic radars, the electric field equations for bistatic high-frequency radars in high sea states are developed. This results in an additional term related to the first-order electric field, which is only present when the small-height approximation is removed. Then, the radar cross-section for the additional term is derived and simulated, and its impact on the total radar cross-section at different radar configurations, dominant wave directions, and sea states is assessed. The proposed term is shown to impact the total radar cross-section at high sea states, dependent on radar configuration and dominant wave direction. The present work can contribute to the remote sensing of targets on the ocean surface, as well as the determination of the dominant wave direction of the ocean surface at high sea states.

First Evidence of Mesoscale Ocean Eddies Signature in GNSS Reflectometry Measurements

Feasibility of sensing mesoscale ocean eddies using spaceborne Global Navigation Satellite Systems-Reflectometry (GNSS-R) measurements is demonstrated for the first time. Measurements of Cyclone GNSS (CYGNSS) satellite missions over the eddies, documented in the Aviso eddy trajectory atlas, are studied. The investigation reports on the evidence of normalized bistatic radar cross section ( σ 0 ) responses over the center or the edges of the eddies. A statistical analysis using profiles over eddies in 2017 is carried out. The potential contributing factors leaving the signature in the measurements are discussed. The analysis of GNSS-R observations collocated with ancillary data from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis-5 (ERA-5) shows strong inverse correlations of σ 0 with the sensible heat flux and surface stress in certain conditions.

Scattering Characteristics of Ultra-Wideband Antenna Arrays

This paper presents a study of the monostatic and bistatic radar cross-section (RCS) of three planar two-dimensionally periodic antenna arrays with the same aperture size: arrays of conductors of variable square cross-section, TEM horns, and rectangular metal waveguides. The results of numerical simulation of the arrays using the finite element method showed that, under normal plane-wave incidence, the monostatic RCS of the array of square conductors is smaller by 10…30 dB than that of the waveguide array in the frequency band wider than 10 : 1. For one linear polarization of the incident plane wave, the RCS of the array of TEM horns is close to that of the waveguide array and, for the other, it is close to the RCS of an array of conductors of variable square cross-section. With an increase in the incidence and observation angles, the difference in monostatic RCS decreases. The scattering patterns of the array of conductors of variable square cross-section for various frequencies and angles of plane-wave incidence are presented and compared with those of the waveguide array under normal incidence.

Broadband corner cloak using a uniaxial transformation medium of stacked artificial dielectric sheets

We demonstrate corner cloak operations mimicking a corner reflector and hiding objects in a truncated corner. The corner cloak is designed at 18.25 GHz and implemented by nonresonant artificial dielectric sheets stacked onto the bottom hypotenuse. It is shown by the near-field measurements that the measured field distributions for the cloak agree well with those for the original area of the corner reflector as well as those for the numerical prediction. The bistatic radar cross-sections (BRCSs) for the cloak and the original area calculated from the measured field distributions coincide with each other and the cloak operation is quantitatively confirmed. The bandwidth evaluated by the specular scattering angles from the BRCSs shows broadband operation as wide as from 16 to 22 GHz.

Multiple Diffuse Coding Metasurface of Independent Polarization for RCS Reduction

In this article, a multiple diffuse coding metasurface (MDCM) of independent polarization is designed to control the propagation direction of diffuse reflections under different polarizations and to improve the monostatic and bistatic RCS (radar cross section) reduction effect. First, a method for controlling the distribution range and propagation direction of the diffuse field is studied, and the diffuse field distribution of the random phase metasurface is optimized by a genetic algorithm to improve the uniformity of the diffuse scattering distribution. Then, the random phase distribution is superimposed on the periodic gradient phase distributions of the linear and hedge types in the orthogonal direction so that the main propagation direction of the diffuse metasurface deviates from the specular reflection region under different polarizations, showing single and two diffuse beams. Finally, the anisotropic unit cell with a rectangle inside and an improved Jerusalem cross on the outside is employed as the basic coding element of the MDCM due to its independent polarization phase response. The numerical and experimental results show that the MDCM features multiple diffuse scattering, independent polarization and angle insensitivity and can efficiently improve the monostatic and bistatic RCS reduction effect simultaneously. Because the scattered energies are redirected away from the specular reflection direction, the specular scattering reduction effect is better than the isotropic diffuse metasurface. The proposed method increases the difficulty of detection by single or netted radar and has the potential for the applications of stealth techniques.

Analysis and Reduction on in-Band RCS of Fabry-Perot Antennas

In this article, a method is proposed to reduce the in-band radar cross section (RCS) of the high-gain Fabry-Perot antenna (FPA) based on the cancellation between the antenna mode RCS (AM-RCS) and structural mode RCS (SM-RCS). The ports of the two back-fed microstrip array antennas are connected to form the partial reflective surface (PRS) with a high reflectivity. The phase delay line (PDL) is proposed to control the AM-RCS to cancel out the SM-RCS. The AM-RCS is used to further reduce the in-band RCS of the low RCS high-gain FPA instead of being eliminated by the matched load. The measured results show that the FPA has a great impedance matching within the band of 9.8-11.2 GHz, and the maximum realized gain of the FPA reaches 10.7 dBi. The simulated bistatic RCS of the FPA is less than -14 dBsm within ±90 degrees angle domain at the center frequency. The minimum monostatic RCS of the proposed FPA is reduced by 17.9 dB compared with the reference FPA. Furthermore, this article provides a design basis for the feed line length of the FPA from the perspective of scattering performance.

Impact on Sea-Surface Electromagnetic Scattering and Emission Modeling of Recent Progress on the Parameterization of Ocean Surface Roughness, Drag Coefficient, and Whitecap Coverage in High Wind Conditions

Ocean surface wind stress is the force generating ocean surface roughness and whitecaps. The surface wind stress is related to the surface wind speed by the drag coefficient. Consequently, the magnitude of roughness and whitecaps calculated from wind speed input depends on the applied drag coefficient formula, which remains uncertain especially for high wind conditions. Because roughness and whitecaps are two major components of the ocean surface response in microwave remote sensing, a clear understanding of the drag coefficient, ocean surface roughness, and whitecap coverage is critical to interpreting the microwave signals emitted or scattered from the ocean surface. In reverse, the microwave signals represent precious data sources of these ocean surface properties [surface wind stress (or equivalently the drag coefficient), surface roughness, and whitecaps] that are difficult to measure with traditional oceanographic instruments, especially in severe weather conditions. This article describes the improvement of ocean surface properties achieved by incorporating microwave remote sensing measurements. In essence, the global data of microwave monostatic and bistatic radar cross sections contribute to the revision of ocean surface roughness spectrum model, and microwave radiometer measurements in tropical cyclones provide clarification regarding the dependence on wind speed of the drag coefficient and whitecap coverage. In return, the calculated excess emissivities and scattering radar cross sections are improved from implementing the updated results of drag coefficient, whitecap coverage, and surface roughness in microwave emission and scattering models.

Modeling the Effects of Topography on Delay-Doppler Maps

A method for simulating delay-Doppler maps (DDMs) of global navigation satellite system signals reflected from land surfaces with heterogeneous terrain is developed from first principles. The method follows previous work for ocean DDMs in the geometric optics limit of the Kirchhoff approximation. Unlike the ocean method, however, where surface heights are assumed to be random with homogeneous statistics, this method decomposes the surface heights into a deterministic part obtained from a digital elevation map (DEM) and a random part representing the residual between the surface and the DEM. The method accounts for the displacement of reflected power into bins of lower delay due to raised surface terrain. The method also provides for the modulation of the normalized bistatic radar cross section by DEM-derived surface slopes over the glistening zone of the DDM. A technique to register Cyclone Global Navigation Satellite System (CYGNSS) DDM bins in delay-Doppler space for land applications is also proposed. The DEM-based method is applied to a CYGNSS track over the Soil Moisture Sensing Controller And oPtimal Estimator (SoilSCAPE) site at Tonzi Ranch, CA, USA. The DEM-based method has potential application for spaceborne monitoring of a variety of environmental parameters.

Three-Dimensional Scattering From Uniaxial Objects With a Smooth Boundary Using a Multiple Infinitesimal Dipole Method

The formulations for three-dimensional (3D) scattering from uniaxial objects with a smooth boundary using a multiple infinitesimal dipole method (MIDM) are introduced. The proposed technique uses two sets of infinitesimal dipole triplets (IDTs), including three co-located orthogonally polarized electric infinitesimal dipoles, distributed inside and outside of a scatterer to construct simulated fields. The dyadic Green’s functions of uniaxial materials are deployed in the MIDM so as to obtain the simulated fields. The singularity issues in using the uniaxial dyadic Green’s functions, which cannot be solved analytically so far for a general uniaxial medium, can be easily eliminated by using the proposed MIDM. In comparison to the traditional single-layered distribution scheme of IDTs, the proposed multiple-layered distribution scheme can handle the scattering from uniaxial objects accurately and efficiently. Several numerical examples are presented to study bistatic radar cross section (RCS) responses under different scenarios. Excellent agreement is achieved by comparing numerical results with those obtained from commercial software packages, while the simulation performance including CPU time and required memory is drastically improved by using the MIDM when computing a general uniaxial material or a relatively larger object. The proposed technique has its merits on simplicity, conciseness and fast computation in comparison to existing numerical methods.

A Dynamically Phase Tunable Metasurface for a Broad Bandwidth Ultra-Low Radar Cross Section

An electrically tunable metasurface is designed for radar cross-section (RCS) reduction application in this paper. It consists of 24 × 24 cells individually loaded with variable capacitors so that their phase profiles can be independently controlled by the bias voltage. Therefore, based on the diffusive scattering principle and reflect-array theory, we arrange the adaptive phase differences between adjacent basic elements and reconfigure the appropriate phase distribution determined by a genetic algorithm (GA) corresponding to the operation frequency. Thus, stable monostatic and bistatic RCS reduction with normal incidence can be realized over a wide band by independently tuning the capacitance of each loaded varactor. Simulation results verify that the bistatic RCS reduction can reach at least 10 dBSm within both 4.2-7.3 GHz and 9.3-11.3 GHz. Simultaneously, the monostatic RCS reduction reaches at least 17.5 dBSm and 14 dBSm within the above two bands, respectively.

Sea Surface Wind Speed Retrieval from the First Chinese GNSS-R Mission: Technique and Preliminary Results

Launched on 5 June 2019, the BuFeng-1 A/B twin satellites were part of the first Chinese global navigation satellite system reflectometry (GNSS-R) satellite mission. In this letter, a brief introduction of the BF-1 mission and its preliminary results of sea surface wind retrieval are presented. Empirical fully developed sea (FDS) geophysical model functions (GMFs) relating the normalized bistatic radar cross-section to the sea surface wind speed are proposed for the BF-1 GNSS-R instruments. The FDS GMFs are derived from the collocated BF-1 observations, the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis data, and the advanced scatterometer (ASCAT) satellite observations. The preliminary tests reveal that the root-mean-square error (RMSE) between the derived wind speed and the reanalysis is 2.63 m/s for wind speeds in the range of 0.5–40.5 m/s. Further comparisons with the ASCAT observations and mooring buoys show that the RMSEs are 2.04 m/s and 1.77 m/s, respectively, at low-to-moderate wind speeds. This study demonstrates the effectiveness of BF-1 and provides a basis for the future GMF development of the BF-1 A/B mission.

Researches on the scattering characteristics in THz band of conductor cylinder coated with parabolic distribution and time-varying plasma media

It is widely acknowledged that inhomogeneous and time-varying plasma can effectively reduce the back scattering radar cross section (RCS) and THz wave has the potential to penetrate the plasma and against the plasma stealth. Therefore, the backscattering and bistatic radar cross section (RCS) of conductor cylinder coated with parabolic distribution and time-varying plasma media in THz wave band are studied by the Runge-Kutta Exponential Time Differencing-Finite Difference Time Domain (RKETD-FDTD) method in this paper. The influences of plasma parameters are analyzed. From both the backscattering and bistatic RCS simulations, it is obviously that inhomogeneous and time-varying plasma cloaking system makes a significant difference on reducing the RCS and improve the plasma stealth while electromagnetic wave in THz region can successfully weaken its influence and contribute to the anti-stealth.

A GNSS-R Geophysical Model Function: Machine Learning for Wind Speed Retrievals

A machine learning technique is implemented for retrieving space-borne Global Navigation Satellite System Reflectometry (GNSS-R) wind speed. Conventional approaches commonly fit a function in a predefined form to matchup data in a least-squares (LS) sense, mapping GNSS-R observations to wind speed. In this study, a feedforward neural network is trained for TechDemoSat-1 (TDS-1) wind speed inversion. The input variables, along with the derived bistatic radar cross-section $\sigma ^{0}$ , are selected after investigating the wind speed dependence and the model performance. When compared to an LS-based approach, the derived model shows a significant improvement of 20% in the root mean square error (RMSE). The proposed neural network demonstrates an ability to model a variety of effects degrading the retrieval accuracy such as the different levels of the effective isotropic radiated power (EIRP) of GPS satellites. For example, the derived Mean Absolute Error (MAE) of the satellite with SVN 34 is decreased by 32% using the machine-learning-based approach.

Scattering and absorption characteristics of graphene coated metamaterial cylinder

Terahertz (THz) wave interaction from graphene coated metamaterial cylinder has been investigated analytically and numerically. The analytical formulation of electromagnetic fields is being modeled in the frame work of Mie theory while the modeling of the graphene is done by random phase approximation method. The causality principle based Kramer-Kroing relations are used to simulate the DNG metamaterial, while the DPS metamaterial is modeled by the Drude relations of SiO2. The analytical formulation is developed for both parallel and perpendicular polarized waves. The impedance boundary conditions (IBC) approach is used to model the infinitely thin graphene coating on metamaterial cylinder. Further the IBC at the interface of graphene layer and metamaterial cylinder are applied to compute the unknown scattering coefficients. The efficiency factors i.e., scattering efficiency (Qsca), extinction efficiency (Qexc) & absorption efficiency (Qabs) and bistatic radar cross section (RCS) have been computed analytically as well as numerically for both micro and nano cores. The influence of graphene parameters i.e., chemical potential (μc) & scattering rate (τ1) and size of metamaterial cylinder (R) on the scattering efficiency (Qsca) and extinction efficiency (Qexc) has been analyzed for DPS and DNG cores. It is observed that the in the nano regime, for perpendicularly polarized wave, graphene coated metamaterial cylinder supports the localized surface plasmon resonance (LSPR) modes and LSPR is found sensitive to the change in the graphene parameters and core size. However, it is reported that the parallel polarized wave has same response towards the DPS and DNG cores in the nano regime. It is concluded that under suitable parameters the graphene coating may provide extraordinary degree of freedom to actively control the THz interactions i.e., scattering efficiency, extinction efficiency and bistatic RCS. The present work may have potential applications in designing and manufacturing of Electromagnetic invisibility, cloaking and target protection devices for THz region.

Ultra‐wideband Low‐Detectable Coding Metasurface

A coding metasurface is designed based on hybrid Array pattern synthesis (APS) and Particle swarm optimization (PSO) method for ultra-wideband low-detectable application. The metasurface is composed of Electromagnetic band-gap (EBG) structures of two Minkowski fractal elements with reflection phase difference of 180° (±37°) over a wide frequency range. Two different types of EBG unit cell printed on a thin grounded dielectric substrate produce reflection phase difference of about 180 degrees over a wide frequency range. Ultra-wideband Radar cross section (RCS) reduction results from the phase cancellation between two local waves produced by these two unit cells. The diffuse scattering of EM waves is caused by the optimization of phase distribution, leading to a low monostatic and bistatic RCS simultaneously. The proposed metasurface can achieve 10 dB monostatic and bistatic RCS reduction in a wide frequency band from 5.8 to 18.0 GHz with a ratio bandwidth (fH/fL) of 3.10:1 under normal incidence for both polarizations. The theoretical analysis, simulation and experiment results are in good agreement and validate the proposed metasurface can achieve ultra-wideband RCS reduction and diffuse scattering.

PCL 운용환경에서 통계적 가설 검정을 활용한 저피탐 표적 식별

In this paper, we propose a new framework of target classification for a passive coherent location(PCL) radar network. The framework uses radar cross sections(RCSs) obtained from multiple bistatic radars, and is computationally more efficient compared with the conventional method that uses time-varying RCSs obtained from a monostatic radar. Firstly, we construct the training set of the bistatic RCS distribution of each target using the scenario-based method and a PCL radar network with multiple transmitters and a receiver. Next, assuming that a test sequence consists of bistatic RCSs, we classify each target using statistical hypothesis test algorithms, such as Z-test, Wilcoxon test, and sign test. The proposed framework demonstrated better performance than the conventional method, in terms of computational efficiency.

Reconfigurable RCS Reduction from Curved Structures Using Plasma Based FSS

The radar cross section (RCS) reduction from curved surfaces using plasma based frequency selective surfaces (FSS) is investigated. A frequency reconfigurable plasma based FSS unit-cell element with target-shaped structure is proposed. The operating frequency of the FSS is governed by the plasma ionization degree (i.e. plasma frequency). zero crossing frequency of the FSS unit-cell has a tuning range extending from 9.6 GHz to 11.3 GHz with an average bandwidth of 1.1 GHz. Planar and curved metallic surfaces are investigated. The curves structures include cylindrical (convex and concave), and spherical (convex and concave) surfaces. Single ionization source is applied at the rare end of the plasma FSS array design is optimized to maintain uniform plasma flow over the metallic surfaces by applying a single ionization source at the rare end of the array. The plasma FSS arrangement with ωp = 9 × 1011 rad/Sec loading a planar sheet reduces the RCS by 23 dB at 10.2 GHz and the (− 5 dB) frequency band of 14.7% for planar plate compared with the unloaded plate case. Different hybrid arrangements are investigated for wideband RCS reduction of 36.4% by superimposing reduction bands of three different plasma frequencies. A 21.5 dB reduction is achieved at 9.8 GHz for FSS arrangements (III). The effect of changing the radii of curvature for convex and concave cylindrical and spherical metallic surfaces is studied at different plasma frequencies. A full-wave analysis of the loaded metallic plates with plasma FSS is used to calculate the backscattered and bistatic RCS for different surfaces.

Analytical Models for the Electromagnetic Scattering From Isolated Targets in Bistatic Configuration: Geometrical Optics Solution

In this article, we present a fully analytical model for the evaluation of the electromagnetic (EM) field scattered from a composite target in a generic bistatic configuration. The scenario comprises a rectangular parallelepiped target with smooth dielectric faces lying over a rough background surface, modeled as a stochastic process. The single- and multiple-bounce scattering contributions arising from the target, the rough background, and their interactions have been derived under the Kirchhoff approximation (KA)–geometrical optics (GO) solution. This framework enables the evaluation of the bistatic radar cross section (RCS) of the considered composite target via closed-form expressions. The proposed model exhibits good agreement with the literature results based on accurate and well-established numerical methods. Our analytical model is therefore proposed as a valid alternative to numerical techniques, being able to provide reliable results at a negligible computational burden. Finally, the role of the main scene parameters, i.e., target orientation, surface roughness, and polarization in the bistatic RCS of the target, have been analyzed and discussed.

A Near-Field to Far-Field RCS Measurement Method for Multiple-Scattering Target

It is challenging to perform the near-field to far-field transformation with a high precision for the multiple-scattering targets using the conventional monostatic radar cross section (RCS) measurement. In this paper, a novel near-field to far-field transformation method with bistatic RCS measurement is proposed. First, the RCS measurement is perceived as a double radiation model. Doing this, the relationship of near-field data and far-field data at different angles is derived, and the convolution function is given under the cylindrical wave. Second, the near-field scattering data are acquired using the proposed bistatic RCS measurement method that combines one transmission and multiple receptions with the rotation of a revolving table. The near-field data are then extrapolated twice with the convolution function, and the far-field RCS are obtained accordingly. Moreover, this paper also analyzes the truncation angular and sampling intervals for the measurement consideration. Finally, the effectiveness and the high precision of the proposed transformation approach for the multiple-scattering target are demonstrated using the numerical simulations and the experimental characterization with an example of dihedral structures.