Variation Of Radar Cross Section Research Articles

Scattering properties of dual Bessel beams on chiral layered particle

The paper investigates the scattering analytical solution of arbitrary direction double zero-order Bessel beams (ZOBBs) incident on a non-uniform layered chiral sphere. Using the generalized Lorenz-Mie theory (GLMT), the electromagnetic field expansion expression of the double ZOBBs is obtained through the vector superposition of the spherical vector wave functions (SVWFs). Analytical solutions of the scattering on chiral layered particles by dual Bessel beams are derived based on the boundary condition. The iterative coefficient equations are constructed to obtain the expansion coefficients of the SVWFs in each region of the multi-layer chiral sphere. The variation of radar cross section (RCS) with angular distribution is numerically simulated, and the scattering results of layered chiral spheres degenerated into isotropic layered spheres are compared with the literature, which verifies the correctness of the theory and program. The effects of incident angle, polarization angle, cone angle and chiral parameters on the scattering characteristics of far region and internal field of the layered chiral particle are analyzed in detail. The theory and results can offer significant assistance in studying the optical properties of non-uniform chiral particles and complex biological cells irradiated by multiple beams and may also provide important practical value in the micromanipulation of multi-layered biological structures.

RCS reduction effect based on transparent and flexible polarization conversion metasurface arrays

In recent years, radar cross section (RCS) reduction techniques based on electromagnetic absorption materials have become a hot research topic in the field of electromagnetic stealth. This paper proposes a transparent conformal encoded metasurface based on polarization rotation units. The metasurface array is optimized using the whale optimization algorithm to construct a 1-bit polarization rotation encoded unit array. The proposed metasurface array exhibits good RCS reduction and electromagnetic wave polarization conversion performance in the frequency range of 13.2–20.7 GHz. The RCS reduction effect of the metasurface array is effective at different angles and polarization states. The metasurface is composed of transparent and flexible materials, namely ITO, PET, and PVC plastic. It exhibits conformal properties while maintaining a high physical transmittance of up to 83.6%. The RCS reduction performance of the metasurface is studied under different curvatures and demonstrates good conformal scattering characteristics. The RCS variation of ITO material compared to traditional metallic materials was also analyzed. It was found that ITO with low surface resistance is an effective means to broaden the RCS bandwidth. This makes it suitable for theoretical research and the design of electromagnetic stealth for electronic devices such as radars and antennas with different curvatures.

Implementation of radar cross-sections model for targets with different scattering centers

Target scattering or reflection is used by radar systems to identify and detect targets. The larger the echo that was returned to the radar receiver, the superior the signal-to-noise ratio and the greater the likelihood of detection. The radar cross-section (RCS) determines the quantity of energy reflected from a target in radar systems. This work shows new modeling for radar targets with growing stages of fidelity. We introduce the RCS concept for straightforward point targets and extend this into additional complex states of targets with several scattering midpoints. In addition, we discuss the modeling of fluctuations in RCS with time and briefly consider the case of the polarized signal. Because the receiver and transmitter are co-located, the effort focuses on narrowband mono-static radar techniques. The RCS value changes between scans. We simulate the replicated power of a sent signal over 10,000 scanning over unit incident signals, assuming that the signal illuminates the target just once each dwell. The target is modeled by four scatterers that are placed at four square vertices. All scatterers are cylindrical-point targets on a 0.5-meter square XY plane without losing generality. The acquired results demonstrated how to generate target echoes while accounting for statistical fluctuations. From the relation between RCS and elevation angle variations for cylindrical targets, the obtained result demonstrated that the first two outputs are the same and confirmed that there is no reliance on azimuth angle. The comparison between wideband and narrowband RCS patterns demonstrated that the RCS profiles of the target-matched shallower nulls for azimuth direction are in the range of (40–50) degrees at zero elevation for 4 scatterers’ extended targets.

Radar Cross Section Modelling and Analysis of Static and Dynamic Targets using MATLAB

Radar Cross Section (RCS) is an important characteristic of the electromagnetic system for target detection. This study presents detailed modelling of Radar Cross Section (RCS) of static simple objects like sphere, cylinder, triangular plate, circular flat plate, truncated cone and complex objects using MATLAB Radar toolbox. The RCS modelling of simple objects is also done with MATLAB POFACET GUI 4.3 and the results are compared with MATLAB Radar tool box. The RCS of complex objects are vectorially added in MATLAB and modelled in this work. Modelling includes 1. A cylinder with a circular flat plate on both ends 2. A circular cylinder with ellipsoid at front end 3. A truncated cone (frustum) with circular plates at both ends 4. The half ellipsoid with a frustum and the flat plate. The simulation and comparison of the RCS variations in dBsm with respect to aspect angle for parameters such as size and frequency of the simple and complex objects have been carried out in this work. RCS of a complex object with dynamic characteristics is also analysed using the Chi-square probability density function. ’The scope of this paper is limited to the objects with deterministic shapes and the combined objects using those shapes. The detailed experimental study on the sphere shows that RCS remains the constant in all directions for sphere. The study also highlights the RCS return is maximum at 180 degrees when the cylinder is aligned horizontally with the RADAR and minimum RCS is obtained at 90 degrees and 270 degrees. In the case of ellipsoid, the RCS is maximum at 90 degrees and 270 degree and minimum at 180 degrees. For the triangular flat plate, the RCS is maximum at 0 degree and 180 degrees and minimum at 90 degrees. For the truncated cone the RCS has maximum and minimum values at aspect angles of zero degrees and 80 degrees. The model of the frustrum with flat plate at both ends provides maximum RCS due to the frustrum and minimum due to flat plate and the normal incidence occurs at 73.3008 degrees. The Swerling models for the fluctuating RCS are also analysed in detail which will be used to measure RCS of high-speed debris revolving around the earth's surface by the radar in Low Earth Orbit (LEO).

Shape preserving topology optimization for structural radar cross section control

The purpose of this paper is to present a shape preserving topology optimization method to prevent the adverse effects of the mechanical deformation on the Radar Cross Section (RCS). The optimization will suppress the variation of RCS on the perfect conductor surface by structural design. On the one hand, the physical optics method is utilized to calculate the structural RCS, which is based on the surface displacement field obtained from the finite element analysis of the structure. The corresponding design sensitivities of topology optimization are derived analytically and solved by the adjoint method. On the other hand, the RCS variation and mechanical performance are taken into account simultaneously by extending a standard compliance-based topology optimization model. Two optimization formulations are discussed in an illustrative example, where the influences of upper limits of the compliance and the RCS variation are considered. Two more examples are further tested to show the ability and validity of the proposed optimization method.

A Highly Sensitive Microwave Patch Sensor for Multidirectional Strain Sensing Based on Near Orthogonal Modes

A passive wireless strain-sensing system for strain monitoring of metallic structures is presented in this paper, wherein single-feed (SF) patch antenna with near orthogonal fundamental modes is initiated as the sensing element. A new approach is proposed by using input admittance of the orthogonal modes as the strain measurand. Strain sensing proof-of-concept of the SF patch-sensor was first established through electromagnetic simulation, then a cantilever beam strain measurement system was designed and employed to quantify the changes of input admittance while directional strain was arising. The simulated results reinforced with mathematical derivation and verified by experimental results to demonstrate that there is a linear relationship between normalized admittance and micro-strain with a high sensitivity factor of 97 ppm/με from simulation. Experimental results also verified that the single patch sensor can monitor the bidirectional (tensile and compressive) strain in multi-directions. An implementation example of the wireless passive sensing system is also presented in a proof-of-concept case. The change of minimum admittance that is linked with the applied strain was realized and interrogated using a monostatic radar system where the maximum radar cross section (RCS) and frequency differences were used as strain measurands. The interrogation method shows the RCS variations and the frequency shifts of the orthogonal modes in correspondence to the directional strains induced at the sensor in four uniaxial scenarios with a high sensitivity factor of 176 ppm/με.

Opportunities and challenges in RCS measurement of 9‐mm bullet model with 77 GHz mmwave COTS radar systems

AbstractThis article indicates a thus far unexplored area of applied research and development to the application and system engineers and researchers from broad engineering backgrounds. Results of a study are presented for measurement of calibrated Radar Cross Section (RCS) of a 9‐mm bullet (projectile) model by using a commercial‐of‐the‐shelf (COTS) millimeter wave Frequency Modulated Continuous Wave (FMCW) radar system operating in 77 to 81 GHz frequency range. The calibrated RCS variation against the aspect angle is measured experimentally, analyzed, and compared with the simulation results which shows fair matching between the two. The opportunities and challenges attached with the use of such COTS systems for development of Hostile Fire Indication (HFI) systems are discussed. This bullet type and this mmwave frequency has not been thus far studied and reported in literature. This may motivate interested individuals/entities to try to measure (at acceptable accuracy before anechoic chamber measurements) RCS of similar low‐size objects by using such low‐cost COTS platforms.

Dynamic radar cross-section characteristic analysis of wind turbine based onscaled model experimental

Accurately acquiring and analyzing the dynamic radar cross-section (RCS) of wind turbine have a great significance to solve the reradiation interference between wind farms and radar stations. Since the results of high-frequency approximation algorithm are only applicable to the qualitative analysis of electromagnetic scattering, it is almost impossible to accurately acquire the dynamic RCS of wind turbine in actual engineering cases. To this end, we proposed to acquire the dynamic RCS of wind turbine based on the scaled model experimental measurement in a large anechoic chamber. The key techniques of setting up the scaled model as well as the experimental platform were described based on the principle of electromagnetic similarity. The accuracy of experimental result is verified by the comparison with numerical calculation and full-sized experiment reported in literature. By using the control variable method, we were able to measure and analyze the amplitude and phase variation of dynamic RCS with frequency, azimuth, and rotational speed, and achieved the transformation of RCS data into engineering practice. This not only lays a foundation for solving the reradiation interference between wind farms and radar stations, but also provides data support for subsequent theoretical research.

Evaluation of Radar Cross Section in Aerial Operations by using POFACETS for a standard Unmanned Aerial Vehicle (UAV)

In military and common applications, radar assumes an exceptionally noteworthy job in exploring the vehicle, recognizing for flying machines, ships and so on. Radar cross section is a measure of a target's ability to reflect radar signals in the direction of the receiver. It is obvious that RCS depends on the shape of the reflecting objects. In this paper, a brief overview of various radars used in surveillance applications and radar cross section (RCS) measurement techniques are presented. The objective of this paper is to illustrate methods for obtaining the Radar Cross Section (RCS) of a typical Unmanned Aerial Vehicle (UAV) for various frequencies in radar bands. UAV technologies have advanced tremendously and are being developed successfully. These features lead UAV to patrol even in civil airspace for civilian applications. These objects operate with small radar cross-section and/or on low altitude which imposes security threat. Keeping this view the RCS of a UAV which are flying in civilian airspace has to be determined drastically for security purposes. Several shapes are considered for the estimation of RCS. The results on the variations of RCS for the above objects as a function of frequency, aspect angle are presented. The POFACETS plays a crucial role and provides the user an easy–to–use GUI that allows the input of all necessary parameters, while preventing erroneous data input and other user errors. In this paper the RCS of sphere, ellipsoid and UAV are determined.

Accurate Analysis of Target Characteristic in Bistatic SAR Images: A Dihedral Corner Reflectors Case.

The dihedral corner reflectors are the basic geometric structure of many targets and are the main contributions of radar cross section (RCS) in the synthetic aperture radar (SAR) images. In stealth technologies, the elaborate design of the dihedral corners with different opening angles is a useful approach to reduce the high RCS generated by multiple reflections. As bistatic synthetic aperture sensors have flexible geometric configurations and are sensitive to the dihedral corners with different opening angles, they specially fit for the stealth target detections. In this paper, the scattering characteristic of dihedral corner reflectors is accurately analyzed in bistatic synthetic aperture images. The variation of RCS with the changing opening angle is formulated and the method to design a proper bistatic radar for maximizing the detection capability is provided. Both the results of the theoretical analysis and the experiments show the bistatic SAR could detect the dihedral corners, under a certain bistatic angle which is related to the geometry of target structures.

Design of Dual-Loaded RFID Tag for Higher Order Modulations

A touchstone for selecting two scattering states for scalar differential backscattering in passive scatterers was introduced by Green in 1963. According to this model, a scatterer has one global minimum and one global maximum scattering states on its $\Gamma $ plane. The variation of radar cross section (RCS) of the scatterer between these two states is monotonic. Thus, to achieve to the highest differential backscattering the scatterer should switch between these two states. In this paper, we verify, by measurements and simulations, that a linear half-wave dipole antenna behaves as predicted by the Green model. However, we show that the RCS of a T-match bow tie antenna over its $\Gamma $ plane cannot be modeled by the Green model and instead the antenna has two maximum scattering states on its $\Gamma $ plane. In the next step, we use dual loading on the T-match bowtie antenna structure. By appropriate selection of the loads, the antenna can provide various scattering states with various magnitudes in 360° phase span in its in-phase and quadrature plane. This feature of the proposed antenna can be used to increase the modulation depth up to 170%, provide a quasi-32-quasi-quadrature amplitude shift keying, and increase the coverage range in backscattering links.

Measure of Temporal Variation of P-Band Radar Cross Section and Temporal Coherence of a Temperate Tree

This paper deals with a ground experiment based on a P-band scatterometer that measured the evolution of the radar cross section (RCS) and coherence of a temperate tree in HV polarization, during four periods spread over nine months, over a cedar tree. Watering of the tree has limited influence in time on the RCS, i.e., limited to around 30 min, but impacts the coherence over a longer period of time. Analysis of the series shows that according to the season considered, clear daily cycles from 1 to 2 dB may appear on the coherence only (autumn) or on both coherence and RCS (spring), whereas in winter, they are absent on both results. It was analyzed in the literature that the variations in RCS are strongly correlated to the variations in the dielectric constant in trunks and branches. In addition, it was shown that the HV RCS presents seasonal trends with a yearly cycle of roughly 3 dB following similar trends reported for trunk moisture content time series.

Electromagnetic scattering characteristics of double S-shape exhaust nozzle with different coating medium parts

As one of the strong electromagnetic scattering source of the aircraft, the radar cross section (RCS) of the nozzle can be reduced by the special geometry and coating microwave absorbing material at the backward direction of the aircraft. In order to simulate the radar scattering characteristics of six coating models and one metal surface model of double S-shape nozzle, the mode combining impedance boundary condition with iterative physical optics (IPO) method is built. Forward and back-forward IPO method and open MP, MPI parallel computing technology are added to accelerate the convergence and reduce computational time. Besides, the ray tracing method is also adopted to improve the efficiency of geometric blanking judgment. The RCS variation regulations of 7 models under X waveband are obtained. The results indicate that coating medium can effectively diminish the RCS of double S-shape exhaust system. Proper coating method can not only reduce the RCS of exhaust system significantly, but also be economical, easy to coat and light-weight. Compared with all parts coating medium model, the model which is only coated at nozzle outlet can reduce microwave absorbing material cost by 73.6% and ensure that the maximal increment of RCS is less than 15.6%. Comparing with the metal model case, The RCS will decrease by at least 18.5%. The improved IPO method can be applied to the RCS evaluation of cavity and the study of coating absorbing material method, and provide technical support for the coating medium model experiment.

Radar backscattering from breaking wind waves: field observation and modelling

In this article, the results of a field study of the Ka-band (37.5 GHz) radar backscattering from breaking wind waves are presented. Radar and a video camera were simultaneously used to measure the radar cross section (RCS) of the whitecap zone and the characteristics of wave-breaking events. A comparison is made between absolute geometrical lengths, areas and orientations of the whitecaps and the RCS of the whitecaps at moderate (45°) and high (70°) incidence angles. A thin vegetable oil film covering the illuminated area was made to minimize background Bragg backscattering from the surface free of breaking-wave features. At high incidence angles, a linear-like dependence between breaking crest length and RCS and no significant azimuthal dependence are found. At moderate angles of incidence, a prominent azimuthal variation of the whitecap's RCS is shown, while a linear-like relationship between the active breaking area and the whitecap's RCS is obtained in presence of the film on the sea surface. The results are compared to the model of quasi-specular reflection from the breaking waves. It is shown that accounting for backscattering from the droplets produced by the breaking crest improves prediction of the whitecap's RCS given by this model at high incidence angles.

Geometric Optics and Electromagnetic Models for Cylindrical Obstacles

A software prediction tool called EPICS (Enhanced Propagation for Indoor Communications Sys- tems) was developed at the ESAT-TELEMIC division of the K. U. Leuven in two versions: a Geometric Optics (GO) version and a Physical Optics (PO) version. However, like many other three-dimensional package, this can only determine the signal in an environment that can be decomposed into (ir)regular hexahedral obstacles (with 6 sides like rectangular blocks, cubes, etc.) or (complex) combinations of them. Although most of the real life environment can be approximated by these hexahedral obstacles, this might lead to some artefacts like periodic radar cross section variations, the need for multiple diffractions to calculate the signal behind a cylindrical obstacle, or reflections that are ignored (e.g., because the approximated side plane is positioned so that a reflection on that plane can not reach the receiver) is existing. To calculate the signal more accurately for those cases, we need to implement curved obstacles into EPICS. In a first step to achieve this goal, the introduction of cylindrical obstacles is investigated. In this paper, the general strategy is discussed. The first step is to determine the different intermediate (i.e., penetration, reflection and diffraction) points on the ray between transmitter and receiver. Efficient computational routines have been written and tested for this purpose, mostly solving the problem first in two dimensions (projected in a plane perpendicular to the axis of the cylinder) and then transforming this solution to the three-dimensional problem. Once these intermediate points have been found, one can start with the computation of the electromagnetic field. In the case of a penetration, the intermediate point(s) can be found very easily (crossing point(s) of a line and a circle) and the electromagnetic computations don't differ from the computations with hexahedral obstacles. For the reflection by a non perfectly conducting surface, the plane wave Fresnel reflection coefficients can be used. Also the finite thickness of the cylindrical walls can be taken into account, using internal (multiple) reflections, if the losses are high or the reflection coefficient of the wall is not to large. For the diffractions, the two-dimensional geometric problem that needs to be solved to find the diffraction points is the determination of the tangent line to a circle (both from transmitter and receiver). Note that both can have two tangent lines, and one might have to match the two corresponding diffraction points. In this case, the electromagnetic computations for the vertical (i.e., field component parallel with the axis of the cylinder) and horizontal polarisation are done separately. An important issue in these computations is the convergence of the series used for the calculation of the field. The reflection points on a cylindrical wall can not be found as easily as in the previous two cases. In general, an iterative process is required. This implies that the search for a good starting value is an important issue. Therefore some efficient computer programs were written to find firstly a good starting value of the Newton- Raphson iteration. As for the electromagnetic computations, one has to take into account that the caustics are transformed after the reflections and thus another amplitude factor has to be taken into account. Although the described routines are not (yet) a part of the EPICS software, new routines based on Geometric Optics (GO) have been written and tested (in matlab) to predict penetration, reflection and diffraction of electromagnetic fields around cylindrical obstacles. This will be used to compute the effects of a curved airport terminal on an Instrument Landing System (ILS).

Reconstruction of Polygonal Cylindrical Targets with Curved Surfaces from Their Monostatic RCS

Target reconstruction algorithm from its monostatic radar cross section (RCS) has been proposed for polygonal cylinders with curved surfaces. This algorithm is based on our previous finding that the main contribution to the back scattering is due to edge diffracted fields excited at a facet of nearly specular reflection direction. Dimension of this constitutive facet of the target is estimated from the local maxima and its lobe width in the angular RCS variation. Half and quarter circular cylinders are used as canonical scattering objects, and their measured and numerically simulated monostatic RCS values have been studied extensively to find scattering pattern characteristic difference between flat and circularly curved surfaces. Thus estimated constitutive facets are connected in order, and this procedure will be continued until the distance between the first and the final edges would be minimized. Our algorithm has been tested for other targets, and it is found that it works well for predicting metal convex targets with flat and curved facets.

Simulations and measurements of a radar cross section of a Boeing 747‐200 in the 20–60 MHz frequency band

HF and VHF low frequency bands provide a promising way to perform radar target recognition. At these frequencies, Radar Cross Section (RCS) behavior is not well known because the scattered field is due to a complex phenomenon where the interactions between the different parts of the structure have a significant contribution, which makes the prediction difficult. A wire model of a commercial Boeing 747‐200 aircraft, developed to be used with the Numerical Electromagnetic Code (NEC), is presented. The reliability of this model has been assessed by comparing the results given by NEC with the measurements made in an anechoïc chamber with a scaled aircraft, and a relatively good agreement was observed between simulations and measurements. The RCS variations of an aircraft along different flight routes have been investigated, and it is shown that it is necessary to know the flight route of the airplane to envisage target identification in spite of the use of the low frequency band.

Frequency and azimuthal variations of radar cross section and their influence upon low-frequency SAR imaging

Low-frequency SAR requires a highly extended synthetic aperture to give a spatial resolution comparable to that of a microwave SAR. As a result, the azimuth angle of the target is varying significantly along the synthetic aperture path. The signal-bandwidth to carrier-frequency ratio is also much larger compared to conventional microwave SAR, giving a fluctuating target response over the frequency band occupied by the transmitted signal. In this paper, the variations of the radar response with frequency and observation angle and their effects upon SAR imaging are analyzed for Mie-scattering spheres and flat plates. The influence of a reflecting sea or ground surface below the target is also discussed. >

Shape of space debris as estimated from radar cross section variations

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Radar measurement of forested areas during OTTER

To test a forest ecosystem model in the Oregon Transect Ecosystem Research (OTTER) project, it is desirable to find forest canopy parameters via radar remote sensing measurements. Conventionally, forest biomass, along with quantities such as the leaf area index, drives the model. However, it is shown from the SAR data collected over the OTTER sites that the backscatter is not uniquely related to biomass. A sensitivity study is carried out using a scattering model to determine the variation of radar cross section as a function of several forest parameters. The results verify the above observation, and lead to the selection of suitable quantities to be recovered via radar experiments. Since this forest scattering model cannot be easily used for inversion of unknown parameters, the use of simplified models in forest parameter estimation schemes is suggested.