The MLFMA basis method for RCS calculation of discontinuous character objects

A combination of the multilevel fast multipole method (MLFMM) and boundary element method (BEM) can solve large scale photonics problems of arbitrary geometry. Here, MLFMM-BEM algorithm based on a scalar and vector potential formulation, instead of the more conventional electric and magnetic field formulations, is described. The method can deal with multiple lossy or lossless dielectric objects of arbitrary geometry, be they nested, in contact, or dispersed. Several examples are used to demonstrate that this method is able to efficiently handle 3D photonic scatterers involving large numbers of unknowns. Absorption, scattering, and extinction efficiencies of gold nanoparticle spheres, calculated by the MLFMM, are compared with Mie's theory. MLFMM calculations of the bistatic radar cross section (RCS) of a gold sphere near the plasmon resonance and of a silica coated gold sphere are also compared with Mie theory predictions. Finally, the bistatic RCS of a nanoparticle gold-silver heterodimer calculated with MLFMM is compared with unmodified BEM calculations.

Adaptive cross approximation (ACA) algorithm as a kind of common matrix compression method is often used to analyze the electromagnetic radiation and scattering problems. In the region of far field, the impedance matrix is compressed by ACA method, and the extracted impedance matrix is accelerated filling by equivalent dipole-moment method (EDM). In the area of near field, the method of moments or the equivalent dipole-moment method is applied for filling the impedance matrix. The iterative near field preconditioning technique is used to solve matrix equation, so that fast calculation of radar cross section (RCS) can be achieved. Numerical results show that the computational efficiency is improved significantly via applying the presented method in this paper without sacrificing much accuracy.

: In a comparison of measured, simulated, and theoretical calculations of radar cross section (RCS), the radar target was a simple missile shape (a cylinder with hemispherical ends). For the measurements, the target was rotated on a turntable from 5 to 365 deg in azimuth, and its RCS was measured with a W-band frequency agile instrumentation radar. (Clutter and noise in the measured RCS data were reduced by spatial filtering.) For modeling the target geometry, the ACAD (advanced computer aided design) geometric modeling program was used to create both an IGES (initial graphics exchange specification) and a facet model. For modeling the RCS, three high frequency prediction codes were used (Xpatch, CADDSCAT, and NcPTD), as well as a point scatter model. Various methods were used to process and simulate the target returns, depending upon the aspect angle. Agreement between the measured and simulated bandwidth averaged RCS values depended on the portion of the target that dominated the radar return: agreement was close for radar returns dominated by returns from the hemispherical ends of the target. However, for aspect angles near broadside to the target (for which the cylindrical part of the target dominated the returns), RCS measurements suggested an interaction between the target and the pylons supporting it.

In R. Mueller et. al. (2006) the design of a UHF direction finding antenna with optimised radar cross section (RCS) was introduced. In the present paper the monostatic RCS of the antenna is characterised up to 18 GHz. Measured results of the RCS are compared to simulated results which are obtained using the new commercially available multilevel fast multipole method (MLFMM) ( U. Jakobus and J. van Tonder, 2005).

Based on the assumption that plasma medium is cold, unmagnetized, collisional and inhomogeneous, a Radar Cross Section (RCS) calculation model for complex targets shielded with plasma is presented. In high frequency region, the plasma that defilading a target can be treated as layered media. In each layer, the plasma is equivalent to a uniform dielectric. Physics Optics (PO), Ray-Tracing method and Wentzel-Kramer-Brillouin (WKB) method are applied to calculate the backscattering field, which is implemented by visual Graphical Electromagnetic Computing (GRECO) platform. Numerical results illustrate that shielding the targets with plasma is a valid way to reduce the RCS of targets. This conclusion has a broad prospect for plasma stealth and anti stealth

The shape and design characteristics of a wing have a strong influence on the radar cross-section of a military aircraft. Little information regarding the airfoil design characteristics on the radar cross-section (RCS) is available in the open literature. This paper studies the change in RCS when the wing with different profiles is subjected to various trailing edge flap deflections. The effect of thickness of the airfoil on the RCS is studied by using NACA 0009, NACA 0012, and NACA 0015 as the wing cross-section shape. A wing with a NACA 0012 airfoil was subjected to various flap deflections to study the change in RCS pattern. The significant variation in RCS and increase in number of lobes was observed as the amount of flap deflection increases. In addition, a comparison of the RCS was done using the three airfoil profiles. RCS dip was highest for a thinner wing, i.e., NACA 0009 and lowest for a thicker wing, i.e., NACA 0015 and for all three wings RCS dip occurs at around 260° observation angle when the flap deflects to 45° in the downward direction. Multilevel Fast Multipole Method (MLFMM), a full-wave technique available in the commercial software FEKO, was used to conduct this study.

Quadcopter is very popular as a consumer electronics, but recently it is also being used on military purpose. To the defence side, detecting the quadcopter is a first priority, and to the offense side, reducing its detectability is important, and both are related to its radar cross section (RCS). We simulate the RCS of a typical quadcopter using the multi-level fast multi-pole method (MLFMM), and then try to reduce its radar cross section by modifying its external shape into a disk type. The results indicate such modification indeed can reduce its RCS to -10 dBsm when the radar wave is incident at horizontal direction, but less effective at other radar wave incident direction.

This article discusses a post-processing method to achieve highly accurate radar cross section (RCS) measurements in challenging test environments. In the ideal RCS measurement setup, the only received signal is the reflection from the object under test (OUT). However, this scenario is often not realizable in practice as outside measurements suffer from a multitude of scattering objects beyond the OUT, and even anechoic chambers have nonnegligible multipath clutter. Time-gating has been shown to be a powerful post-processing clutter suppression tool by temporally filtering any undesired return signals. However, this technique is only sufficient when there is ample spacing between the OUT and undesired return signals or when the sidelobes of one scatterer do not mask the return of a smaller nearby scatterer in the time domain. In the latter scenario, traditional time-gating techniques cannot separate the sidelobes from a nearby dominant scatterer overlapping with the main lobe of the OUT, and the RCS of the OUT cannot be extracted accurately. By applying the proposed stepped frequency continuous wave (SFCW) adaptive pulse compression (APC) algorithm, a range-dependent filter is created to iteratively estimate the range profile and suppress sidelobes allowing for temporal separation of the scatterers and accurate RCS estimation. To validate the concept, the RCS of a 15.2 cm sphere is extracted in two measurement configurations (with and without a large nearby dominating scatterer). The traditional matched filter data processing accuracy is compared to the proposed APC technique. Implementation of APC in post-processing yields a 71.2% improvement in average RCS error compared to traditional processing in the sphere-only measurement and an 88.2% improvement in the presence of a metal plate.

This study presents the numerical results for the aerodynamic and electromagnetic performances of an S-duct caret intake. Using the multilevel fast multipole method (MLFMM) to solve Maxwell equations, the current on the intake surface is calculated, and the radar cross-section (RCS) is analyzed. Moreover, the intake flow field is numerically investigated using the SST k–ω turbulence model to solve the Reynolds-averaged Navier–Stokes equations. Compared to a straight intake, for an S-duct caret intake, the average RCS is lower by 7.65 dB, and the maximum RCS difference value caused by the blade rotation is lower by 6.75 dB. However, the flow capacity deteriorates when the total pressure recovery coefficient decreases by 0.004. Based on the analysis of the aerodynamic and electromagnetic characteristics of different intakes, a double S-duct intake is designed. Compared to a traditional S-duct intake, for the novel intake after model parameter modification, the average RCS is lower by 0.05 dB, and the total pressure distortion (TPD) is lower by 0.18. The analysis of the effects of different boundary-layer bleed systems shows that the symmetrical layout adversely affects the aerodynamic and electromagnetic performances of the S-duct intake, but the unilateral partial layout is beneficial, whose TPD is lower by 0.04 and average RCS is higher by −2.17 dB compared to a straight intake.

This communication presents a physical optics based method developed by CELAR to calculate radar cross section (RCS) in function of the distance separating the target and the radar system. Initially this method has been developed to calculate RCS in the same geometrical configurations than the measurements performed in the CELAR facilities. So, after a short presentation of RCS measurement facilities of CELAR, this paper will expose the method developed to calculate near field RCS. Comparisons between measurements and calculations will be shown to validate the method. Then, some applications will be given on canonical and complex targets. For flat circular and square plates, particular phenomena will be detailed and some analytical approximated formula will be proposed to express their monostatic specular RCS

Numerical calculation of radar cross section (RCS) at high frequency is quite challenging. In this correspondence, we apply the Cauchy method and TLS theory to RCS data at a low‐frequency band and predict RCS data at a high‐frequency band. The numerical demonstration shows that the proposed approach generates an estimation that falls within the acceptable error range.

In this paper, the problem of wideband radar cross section (RCS) calculations with asymptotic waveform evaluation (AWE) accelerated method of moments is considered. The traditional formulation, with RCS obtained independently for each frequency, based on Pade approximation of the current distribution is compared to the formulation where rational functions are used to directly approximate far fields. It is shown that an additional approximation used in the second attitude, may reduce the resulting bandwidth of the model.

This work studies the use of simplified geometric models to represent vehicles for Integrated Sensing and Communication (ISAC) systems. Four simplified models: a simple cuboid, a curved cuboid, two curved cuboids, and a modified two curved cuboid, are designed based on the dimensions of a real car (VW Sharan). Their bistatic radar cross sections (RCS) are simulated using the multilevel fast multipole method (MLFMM) in Ansys HFSS and compared to that of the full-scale vehicle model using cross-correlation and median of absolute error (MedAE) metrics. Among the proposed models, the modified two curved cuboid shows the closest resemblance to the scattering response of the VW Sharan.

Radar Cross Section (RCS) essentially relates to low-observable technology. Most of the aerospace structures are close to cylindrical shape. The scattering problems often involve objects that are quite large in terms of wavelength, hence the matrix equations obtained using numerical methods such as Method of Moments (MoM) are large in size and computationally complex. In this paper, RCS of circular, elliptic and semi elliptic dielectric cylinder is computed using MoM. In order to reduce computational cost, conjugate gradient-based accelerating algorithm is employed. It is shown that the computational time is reduced significantly when accelerating algorithm is incorporated into RCS computations.

An engineering approximation of the edge-guided wave contribution to radar cross-section (RCS) calculations is investigated. A dyadic diffraction coefficient is extrapolated from the representation of the edge-wave diffraction mechanisms associated with a dipole radiating in the close vicinity of the edge of a trihedron. The edge wave excited by the tip of a vertex and guided along an edge is derived from reciprocity. The rediffraction of the edge-guided fields is evaluated via multiplication with the proper edge-wave vertex diffraction coefficient. RCS calculations and time-domain extraction techniques are employed to assess and validate edge-wave diffractions from a flat plate, in comparison with method of moments computations and measured data.