Target Radar Cross Section Research Articles

Discrimination of active false targets in multistatic radar using spatial scattering properties

The anti-jamming methods available in multistatic radar are mostly based on data fusion processing and therefore do not fully explore its anti-jamming ability. In the view of multistatic radar, the echoes of real targets received by the widely separated receivers would be independent from each other due to the independence of target radar cross sections in different scattering directions. However, the deception jamming received by the same receivers would be highly correlated since the jamming signals transmitted to different directions are identical. Therefore, real targets would differ from false targets in the spatial scattering property in multistatic radar. By exploiting this phenomenon, a new signal fusion-based method for discriminating active false targets from desired real targets is proposed in this study based on Neyman–Pearson lemma. In this method, false targets are identified by correlation test between the complex envelopes of arbitrary two targets in different receivers. The new method can discriminate false targets generated by deception signals with arbitrary modulation. The closed-form expression for the rejection probability of false targets is derived. Both theoretical analysis and simulations verify the feasibility of the proposed method.

Spatiotemporal radar target identification using radar cross-section modeling and hidden Markov models

We propose a target identification scheme exploiting the temporal dependency and spatial structure of radar cross-section (RCS) measurements in low-frequency, passive, or long-range surveillance radar systems. We employ target RCS modeling integrated into a hidden Markov model (HMM) with state-duration modeling. Assuming that the radar system ensures a sufficient sampling time, it is possible to use the spatial characteristics of airborne targets, because there is consistency between successively sampled RCS measurements. In addition, to exploit the whole temporal characteristic of the sequence of RCS measurements,which has rarely been considered in the literature, we adopt the HMM and target RCS modeling. To accomplish this task, we accurately develop target RCS models and establish the relationship between the target-sensor orientations, which are the hidden states of the HMM, and the correspondingRCSmeasurements. The proposed target identification scheme, which only uses the sequence of RCS measurements, is demonstrated with simulation results and an analysis for various signal-to-noise ratios and target-fluctuation models.

Visual Computing of Complicated Target with Radar Absorbing Material

Radar-absorbing materials (RAM), which effectively reduce the radar cross section of targets, are extensively used in stealth optimization of targets. Graphic electromagnetic computing (GRECO) uses graphic acceleration cards and Z-Buffer techniques to address blanking and non-visibility issues in traditional electronic magnetic algorithms. The traditional GRECO is improved to overcome its inability to precisely extract geometric information on visible surfaces and the dependence of calculation accuracy on screen resolution. An algorithm that can calculate the multiple scattering of metal dihedral-coated RAM is proposed. In addition, the element search method used in traditional dihedral calculation is improved, and calculation time is reduced by a significant margin. After the experimental results were compared, the accuracy of the algorithm is examined. The proposed algorithm, combined with the improved GRECO, can used to analyze the stealth performance of complicated targets coated single- or multi-layered RAM.

Low RCS Target Tracking in Estimated Rapidly Varying Sea Clutter Using a Kronecker Product Approximation Algorithm

We propose a method for estimating the space-time covariance matrix of rapidly-varying sea clutter following a dynamic state space matrix model. The covariance matrix dimension can become computationally infeasible as it increases with the number of range bins and dwell pulses required for coherent processing. In order to reduce the computational complexity, we apply the Kronecker product (KP) approximation and particle filtering to estimate the space-time covariance matrix, and we demonstrate the proposed method's validity using real clutter data. We also demonstrate that the method ensures that the covariance matrix estimate is always positive definite. The covariance matrix estimation is integrated with a track-before-detect filter for tracking a low radar cross-section (RCS) target in strong sea clutter.

Target Recognition Algorithm Based on RCS Time Sequence

Radar Cross Section (RCS) is the information available for nearly all types of radar. RCS is related with lots of factors, therefore the value of RCS of single batch fluctuates greatly, so that fails to extract the space target character. How to use RCS data of space target effectively has the vital significance to improve the target recognition ability of active narrow-band radar. The paper adopts target RCS time series to recognize the target. The existed track data is used to form track information base, radar track matching algorithm based on related functions is presented for the real-time matching of the current dynamic track and the previous track data for the purpose of rapidly finding their RCS time series under the same visual directional angle. A new kind of non-linear and non-stationary time frequency analysis approach Hibert-Huang Transform is then introduced in the paper to decompose the above RCS time series, and then the character index for recognition are extracted from independent intrinsic mode function obtained by the decomposition and the effective target recognition standards are set. The effectiveness and stability of the algorithm presented in the paper are verified by simulated data.

Multi‐angular ground‐based SAR system for soil surface roughness characterisation

Developped in the Institut of Electronics and Telecommunication of Rennes (IETR), a Ground Based (GB) SAR system is proposed for soil surface roughness discrimination at C-band. By using this GB-SAR system, the multi-angular SAR measurement is realized at different resolution cell sizes. The specific levels of surface roughness are set deliberately to analyze the roughness contribution on multi-angular SAR signature in a controlled experimental condition. Based on the GB-SAR measurement, the effect of incidence angle on SAR sensitivity is studied under two resolution cell sizes for retrieving soil surface roughness. The results show that, by using our GB-SAR system, high incidence angle configuration (e.g. > 40 •) is optimal to discriminate surface roughness, which is more significant at small resolution cell size (e.g. 30 cm). This study indicates the effectivity of GB-SAR system to validate the SAR backscattering mechanisms and will be helpful for future spatial missions [1]. Introduction: With high spatial and temporal resolution, the remote sensing techniques play an important role in monitoring the soil status. Compared with optical remote sensing, the synthetic aperture radar (SAR) in independent of weather and light constraint, owing to the active microwave generation and the penetration ability of microwave. Nevertheless, the mechanisms of SAR backscattering from bare soils are suffered from the coherent superposition of surface roughness contribution with soil moisture. Thus, discrimination of surface roughness effect on SAR signature is crucial for further soil monitoring. Recently, the multi-angular SAR measurements increase the observing dimension [2], making it possible to improve the robustness of soil parameter retrievals. However, the temporal interval of spaceborne multi-angular image acquisitions induces several problems in the multi-angular SAR study: i) the soil characteristics may vary during the multi-angular measurements; ii) it is challenged to accomplish the consistent ground truth measurements over large areas simultaneously with satellite pass. To solve the aforementioned issues, this study proposes a Ground Based (GB) SAR system for bare soil monitoring. This kind of GB-SAR system was also developed for terrain mapping [3], vegetation monitoring [4] and snow pack imaging [5]. However, our study concentrates on the bare soil characterization under multi-angular configuration and the influence of resolution cell size on the multi-angular SAR sensitivity. GB-SAR system for soil monitoring: Our GB-SAR system is mainly comprised of three components: i) A vector network analyzer; ii) Four wide band horn antennas (2-12 GHz); iii) A three-meter long metal rail with an accurate positioning motor. This GB-SAR system is capable of measuring the backscattering matrix of targets under controlled experimental condition. Repeatable measurements can be realized by the GB-SAR system as the motion of the platform is controlled accurately, which is essential for multi-angular SAR measurements. Furthermore, different soil status can be set deliberately in the scene to analyze the induced response in SAR signature. The SAR back projection algorithm [6] makes possible to obtain the absolute backscattering coefficients through several calibration procedures: i) The antenna patterns are compensated along both azimuth and range axis; ii) The methodology proposed by [7] is used to accomplish the polarimetric calibration; iii) The radiometric calibration is realized by comparing the measured RCS (Radar Cross Section) of a canonical reference target with its theoretical RCS value.

Distributed MIMO chaotic radar based on wavelength-division multiplexing technology.

A distributed multiple-input multiple-output chaotic radar based on wavelength-division multiplexing technology (WDM) is proposed and demonstrated. The wideband quasi-orthogonal chaotic signals generated by different optoelectronic oscillators (OEOs) are emitted by separated antennas to gain spatial diversity against the fluctuation of a target's radar cross section and enhance the detection capability. The received signals collected by the receive antennas and the reference signals from the OEOs are delivered to the central station for joint processing by exploiting WDM technology. The centralized signal processing avoids precise time synchronization of the distributed system and greatly simplifies the remote units, which improves the localization accuracy of the entire system. A proof-of-concept experiment for two-dimensional localization of a metal target is demonstrated. The maximum position error is less than 6.5 cm.

Backscattering measurements of plasma coated target in high-enthalpy wind tunnel

When high-speed vehicles enter into the atmosphere, plasma sheath may be excited around due to aerodynamic heating, resulting in difficulties in communicating and changes of electromagnetic scattering properties. Those facts have received lots of attention due to their influences on the aerospace communication and radio telemetry applications. While analytic and numerical studies have been carried out by many native institutions on the electromagnetic radiation/scattering problems in the presence of plasma sheath, there remains the lack of measurement data to support and verify those researches. This work reports the backscattering measurements for the target surrounded by plasma sheath in the ground high-enthalpy shock tunnel facility. Using the step frequency sweeping mode of a commercial instrument, i.e., vector network analyzer, we conduct the experiments in the JF-10 high-enthalpy shock tunnel. The dynamic electromagnetic scattering measurement must be completed on a time scale of ms while the shock tunnel is running. The implementation details are demonstrated in this work, including the experimental configurations, data processing procedures, timing synchronization, and discussion on the relationships between the air flow status and measured target scattering signals. The influences of the plasma sheath on the target RCS (radar cross section) in the C band are successfully and clearly observed. The influence of the air flow status on the measured data can be concluded as follows: the front section of high-speed air flow lasting about 0.5-1 ms will change the measured signal dramatically, which should be avoided in observation due to its instability; the effective plasma sheath lasts only about 2 ms, resulting in an overall reduction on the target RCS by about 2 dB in the measurements. Afterwards, the effects by the plasma sheath on the target scattering vanish quickly.

The Simultaneous Interpolation of Target Radar Cross Section in Both the Spatial and Frequency Domains by Means of Legendre Wavelets Model-Based Parameter Estimation

The understanding of the target radar cross section (RCS) is significant for target identification and for radar designing and optimization. In this paper, a numerical algorithm for calculating target RCS is presented which is based on Legendre wavelet model-based parameter estimation (LW-MBPE). The Padé rational function fitting model applied for MBPE in the frequency domain is enhanced to include spatial dependence on the numerator and denominator coefficients. This allows the function to interpolate target RCS in both the frequency and spatial domains simultaneously. The combination of Legendre wavelets guarantees the convergence of the algorithm. The method is convergent by increasing the sampling frequency and spatial points. Numerical results are provided to demonstrate the validity and applicability of the new technique.

Improving Target Detection Accuracy Based on Multipolarization MIMO GPR

In this paper, we combine the multiple-input-multiple-output (MIMO) array antenna technology with a multipolarization component in a ground penetrating radar (GPR) system to improve target detection accuracy. The MIMO technology introduced in previous literature is widely applied in radar and other wireless communication fields. Here, we apply the MIMO technology with a “plane-wave like” (PWL) source that uses array antennas with small spacing to emit a pulse source at the same time in GPR detection. First, we analyze the physical mechanism of the MIMO GPR system with a “PWL” source to improve the target detection resolution. Then, we carry out a numerical simulation with a finite-difference time-domain method in 1-D and 2-D array antennas to compare the imaging results of the MIMO and traditional GPR systems. Finally, the synthetic data MIMO GPR experiment with a step-frequency GPR system is implemented. Compared with the traditional GPR system, our results demonstrate that the MIMO GPR system with a multipolarization detection mode can overcome the influence of target radar cross sections and antenna radiation directions, and improve target detection accuracy effectively. Meanwhile, the synthetic MIMO GPR system also provides a good idea to improve the system performance and reduce system design requirements and the manufacture cost.

An Adjustable Radar Cross Section Doppler Calibration Target

This paper describes the development of a simple low-cost adjustable radar cross section (RCS) Doppler calibration target. It consists of a small metal sphere attached to the diaphragm of an ultrasound transducer. It is shown that the effective RCS of the target is a function of the physical RCS determined by the size of the sphere, and the magnitude of the displacement introduced by the transducer. A simple Michelson's interferometer was constructed to determine the magnitude of these displacements, and a linear relationship between the applied sinusoidal voltage (at resonance) and the displacement is determined. Measurements made using a sensitive Doppler radar confirm the calculated RCS to an accuracy of better than 2 dB, and show that it can be adjusted over 20 dB by adjusting the transducer excitation voltage through one decade. These low RCS targets are ideal for testing radio acoustic sounding systems and entomological radars.

Numerical and experimental studies of target detection with MIMO radar

Spatially diverse multiple-input multiple-output (MIMO) radar systems combine multistatic measurements of the target under view into a single detection algorithm and are thereby expected to alleviate the effects of fading on target radar cross sections (RCS) as the angle of observation is varied. Previous analytical studies of target detection for this case have shown that MIMO radar detection performance can exceed that of the corresponding phased array radar if both sufficient spatial diversity and signal-to-noise ratio (SNR) are achieved. These results have been based on a statistical model for the multistatic RCS of the target that is similar to the traditional Swerling models of the monostatic RCS. The degree to which these results are applicable to specific target geometries therefore remains uncertain. To address this issue, two studies of MIMO radar target detection incorporating realistic RCS properties for specific target geometries were performed. The first study utilized a numerical method to compute the multistatic RCS of a helicopter-like target observed at center frequency 200 MHz, while the second involved radar measurements of an unmanned aerial vehicle (UAV) target at 2.75 and 4.5 GHz. MIMO radar configurations having two transmitters and either three (for the radar measurements) or four (numerical simulations) receivers were used. In both cases, multistatic received fields were combined with regulated thermal noise levels in postprocessing to study target detection performance. Because in general the azimuthal orientation of a specific target with respect to the radar is uncertain, the detection performance results shown are averaged over the azimuthal orientation angle of the target. The average over target orientation can also be interpreted as similar to an average over “trials” of a statistical target description, enabling comparisons of field properties averaged over target orientation with similar ensemble averages from the statistical models of the literature. Although detection performance curves for the specific targets considered are not identical to those predicted analytically by the statistical target model, results for these targets confirm that the MIMO radar system can achieve enhanced detection performance as compared with the corresponding phased array radar system.

Performance bounds of direction finding and its applications for multiple‐input multiple‐output radar

In this study, the authors derive an explicit expression for Cramer–Rao lower bound (CRLB) on direction parameters with the antenna locations of a single point target in the far-field scenario for multiple-input multiple-output (MIMO) radar, firstly. Since there are two unknown nuisance parameters (target radar cross section and interference-plus-noise strength), the authors use the concentrated CRLB to simplify the analytical computation. Then, the authors derive two sets of necessary and sufficient geometrical constraints for direction estimation with both bistatic and monostatic MIMO radars. Then, the authors consider the bounds on the asymptotic normalised mean-square angular error (ANMSAE), which are useful measures in three-dimensional bearing estimation problems. The authors derive the expressions for ANMSAE in both bistatic and monostatic MIMO radars, and discuss them in terms of the antenna locations. The authors then show that the uncoupled geometrical conditions are also sufficient to ensure that ANMSAE is independent of azimuth. Finally, the authors extend those conditions to obtain two sets of geometry constraints for bistatic and monostatic MIMO radars, respectively, such as some kinds of symmetry on the geometry, that ensure the optimal performance is isotropic, that is, the ANMSAE bounds are independent of all direction parameters. In numerical examples section, the authors give several representative antenna geometries to illustrate the derived antenna geometry strategy.

IMPROVEMENT OF ITERATIVE PHYSICAL OPTICS USING THE PHYSICAL OPTICS SHADOW RADIATION

The prediction of Radar Cross Section (RCS) of complex targets which present shadowing efiects is an interesting challenge. This paper deals with the problem of shadowing efiects in the computation of electromagnetic scattering by a complex target using Iterative Physical Optics (IPO). The original IPO is limited to cavities applications, but a generalized IPO can be applied to arbitrary geometries. This paper proposes a comparison between the classical PO approach and a physical approach based on shadow radiation (around forward direction) with PO approximation for the consideration of shadowing efiects in generalized IPO. Based on the integral equations, a rigorous demonstration of this physical shadowing is provided. Then simulation results illustrate the interest of using physical shadowing both from the transmitter and towards the receiver, compared to the classical approach. Computing electromagnetic signature of complex targets presenting shadowing efiects is a complex problem for which many solutions have been proposed. Each of these solutions presents beneflts and drawbacks, and two difierent kinds of methods can be used for arbitrary shaped cavities: rigorous numerical methods and asymptotic methods. Numerical methods, like Method of Moments (MoM), can be used to calculate RCS (Radar Cross Section) of targets with a good precision. These methods, which do not apply any approximation (but approximation linked to meshing), are known to provide excellent results, but their complexity is high. MoM has a complexity of O(N 3 ), N being the number of unknowns (which is equal to the number of non boundary edges of a meshed target). Thus, in case of great target's dimensions (compared to wavelength), these methods are generally not used, due to their computing time and memory requirement. Nevertheless, MoM will be used in this paper as a reference method. To overcome this issue, asymptotic methods have been developed and can be used in high- frequency domain for arbitrarily shaped targets with a reduced complexity. These methods are based on Geometrical Optics (GO), based on ray trajectories, and/or Physical Optics (PO), using surface currents to calculate scattered flelds. When multiple re∞ections occur, PO is generally preferred to GO, as GO is less precise, particularly in case of highly curved geometries. Iterative Physical Optics (IPO) (1{3) is an asymptotic method based on PO. The method has been originally developed to calculate RCS of cavities (1) and has been generalized to arbitrary geometries (4). This method can be described by an algorithm in 4 steps:

HIGH-FREQUENCY METHOD FOR TERAHERTZ RADAR CROSS SECTION OF CONDUCTIVE TARGETS IN FREE SPACE

The high-frequency method for the prediction of the terahertz (THz) radar cross section (RCS) of conductive targets with extremely electrically large size in free space was presented. In order to consider the scattering flelds of the perfectly electric conducting (PEC) targets with extremely electrically large size in free space, the Green's function was introduced into the conventional physical optics (PO) method which was combined with the graphical electromagnetic computing (GRECO) method and improved using the partition display algorithm. The shadow regions were eliminated quickly by displaying lists of OpenGL to rebuild the targets, and the geometry information was attained by reading the color and depth of each pixel. The THz RCS of conductive targets can be exactly calculated in free space. The RCS comparison between the partition display GRECO prediction by the self-written Visual C++ 2010 program and the simulation of FEKO software with the large element PO method proves the validity and accuracy of the proposed method. The results provide an important basis and method for the potential applications of THz radar in many flelds such as military, astronomy and remote sensing.

Design and Implementation of Radar Cross-Section Models on a Virtex-6 FPGA

The simulation of radar cross-section (RCS) models in FPGA is illustrated. The models adopted are the Swerling ones. Radar cross-section (RCS) which is also termed as echo area gives the amount of scattered power from a target towards the radar. This paper elucidates the simulation of RCS to represent the specified targets under different conditions, namely, aspect angle and frequency. This model is used for the performance evaluation of radar. RCS models have been developed for various targets like simple objects to complex objects like aircrafts, missiles, tanks, and so forth. First, the model was developed in MATLAB real time simulation environment and after successful verification, the same was implemented in FPGA. Xilinx ISE software was used for VHDL coding. This simulation model was used for the testing of a radar system. The results were compared with MATLAB simulations and FPGA based timing diagrams and RTL synthesis. The paper illustrates the simulation of various target radar cross-section (RCS) models. These models are simulated in MATLAB and in FPGA, with the aim of implementing them efficiently on a radar system. This method can be generalized to apply to objects of arbitrary geometry for the two configurations of transmitter and receiver in the same as well as different locations.

Transmit Waveform Optimization for Spatial-Frequency Diversity MIMO Radar in the Presence of Clutter

Benefitting from the independent target echoes of diversity channels, diversity MIMO radar can efficiently improve system performance, such as target detection and parameter estimation. Due to the fact that the RCS (radar cross section) of complex target may vary with the different transmitted carrier frequencies and array geometries, many recent researches study at the background of diversity MIMO radar equipped with widely separated array antennas or working at multiple carrier frequencies, respectively. In this paper, a new MIMO radar system combining the spatial and frequency diversities is investigated in the presence of signal-dependent clutter, which is called spatial-frequency diversity MIMO radar. With the prior information of target and clutter, a new method for joint optimization of transmitted waveforms and receiving filters is proposed to enhance the target detection ability of spatial-frequency diversity MIMO radar. Inspired by the MIMO communication system, the water-filling algorithm is introduced into the transmitted energy allocation problem for each carrier frequency channel. Simulation results show that the proposed system has a better performance in output signal-to-clutter-noise ratio (SCNR) compared to conventional diversity MIMO radar system.

Cued search algorithm with uncertain detection performance for phased array radars

A cued search algorithm with uncertain detection performance is proposed for phased array radars.Firstly,a target search model based on the information gain criterion is presented with known detection performance,and the statistical characteristic of the detection probability is calculated by using the fluctuant model of the target radar cross section (RCS).Secondly,when the detection probability is completely unknown,its probability density function is modeled with a beta distribution,and its posterior probability distribution with the radar observation is derived based on the Bayesian theory.Finally simulation results show that the cued search algorithm with a known RCS fluctuant model can achieve the best performance,and the algorithm with the detection probability modeled as a beta distribution is better than that with a random selected detection probability because the model parameters can be updated by the radar observation to approach to the real value of the detection probability.

Analysis of backscattering RCS of targets coated with parabolic distribution and time-varying plasma media

The backscattering radar cross section (RCS) of targets coated with parabolic distribution and time-varying unmagnetized plasma is analyzed by the finite-difference time-domain (FDTD) method based on the Runge–Kutta exponential time differencing (RKETD) technique. The two-dimensional RKETD-FDTD formulations are derived. The effects of the plasma parameters on the RCS are investigated. The numerical results illustrate that plasma cloaking system can successfully reduce the backscattering RCS, the plasma stealth is effective, and reasonable selection of different parameters of plasma can enhance its effectiveness.

Estimation of Extended Targets using the Generalized Monopulse Estimator: Extension to a Mixed Target Model

In many radar applications extended targets appear together with point targets. An important problem in particular for tracking algorithms is to rapidly detect these extended targets and to determine their centroid and shape. In a previous paper we have developed and characterized estimators for the centroid and extension of an extended target based on the generalized monopulse ratio when the target is modeled as a number of independent Swerling I-II point scatterers. However, the Swerling I-II model is a very rough approximation for the behavior of a real complex target. The work presented here extends the statistical characterizations to mixtures of independent Swerling I-II point scatterers and deterministic Swerling 0 point scatterers which may, however, vary arbitrarily in time. Such a mixture of deterministic and stochastic scatter model is able to provide good approximations of real target radar cross sections.