Efficient RCS Computation Over a Broad Frequency Band Using Subdomain MoM and Chebyshev Approximation Technique

The method of moments (MOM) in conjugation with the best uniform rational approximation is applied to predict the broad-band radar cross-section of arbitrarily shaped three-dimensional (3D) bodies. The surface integral equations are solved using MOM to obtain the equivalent surface currents at the frequency points corresponding to the Chebyshev nodes, and then the surface current within the given frequency band is represented by the Chebyshev series. To improve the accuracy, the Chebyshev series is matched via the Maehly approximation to a rational function, which can be as good as the best uniform rational approximation. Using the rational function, the surface current is obtained at any frequency point within the frequency band. Numerical results for 3D arbitrarily shaped perfectly electric conducting objects and homogenous dielectric bodies are considered. Compared with the asymptotic waveform evaluation technique and the model-based parameter estimation, the proposed technique is accurate in much broader frequency band with lower memory required.

To predict the three-dimensional radar cross section (RCS) pattern of an arbitrary shaped perfectly electric conductor objects in both a broad frequency band and angular domains simultaneously, the method of moments (MoM) combined with the Chebyshev polynomial approximation is presented. The induced current is expanded by a bivariate Chebyshev series. Using this function, the induced current can be obtained at any frequency and angle within the desired frequency band and angular domains. Numerical results show that the proposed method is found to be superior in terms of the CPU time to obtain the three-dimensional RCS pattern compared with the direct solution by MoM repeating the calculations at each frequency and angle. Good agreement between the presented method and the direct MoM is observed.

In this letter, the compressive sensing (CS) is utilized to accelerate the matrix filling procedure of the traditional method of moments (MoM). Instead of constituting a fully populated matrix as the traditional MoM typically does, the CS technology allows one to establish an underdetermined linear system, and the unknown induced currents can be reconstructed by finding the smallest possible $\ell _1 $ norm solutions to the underdetermined linear system. Thus, the number of computations required for constructing the impedance matrix and for solving the unknown induced currents can be reduced dramatically. The ideas can be exploited in the context of bistatic scattering from an arbitrary target. Numerical simulations are presented, and the results are compared to those obtained from traditional MoM to illustrate the validity and the efficiency of the proposed method.

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.

The application of a tapered resistive card to reduce the EM scattering from the edge of an impedance wedge is presented. The problem is two‐dimensional, where the incident field is polarized transverse magnetic or electric to the axis of the wedge, and the resistive card is infinitesimally thin and is attached to the vertex of the wedge. An integral equation is formulated to solve for the scattering from the structure which utilizes a specialized Green's function for the impedance wedge. The integral equation is then solved using a method of moments technique. Since the presence of the wedge is taken into account by the Green's function, unknowns need to be placed only over the region of the resistive card and not along the boundaries of the wedge, thus reducing the size of the moment method matrix. Numerical optimization techniques are then employed to determine the resistance profiles for the cards which yield designs that minimize the scattered field over broad spatial regions and over broad frequency bands as well. The resulting designs for the resistive cards have therefore been optimized to yield maximum performance for scattering reduction. The application of this work to the reduction of edge diffraction from the edges of the ground plane of a microstrip antenna is also discussed, and measured as well as calculated results are presented.

A novel solver for simulation of flows from continuum regime to rarefied regime at moderate Knudsen number

The behavior of reradiated fields from PCBs, with the radar cross section being the main parameter of interest is investigated in this work. A rigorous approach to predict radiation from PCBs in a GTEM cell is presented. The analysis is based upon the use of the reciprocity theorem in combination with the method of moment applied to the scattered field. Thus, yielding a generalized impedance matrix, whose determinant represents the characteristic polynomial of the scattering system. The effectiveness of the method is demonstrated by investigating some canonical circuit configurations and structures illustrating sources of fundamental EMI mechanism. The validity and the accuracy of the analysis becomes obvious in view of the one-to- one correlation with measurements. I. INTRODUCTION Printed-Circuits Boards (PCB) are of overriding importance in modern microelectronics where they undergo a continu- ous package complexity. Multilayer structures, split reference planes, various interconnects like bends, vias, etc. and trace circuit configurations in form of rectangular/circular loop, bent wire, linear dipoles, etc., are commonly mounted and present on hihgly integrated PCBs. These structures have led to an upsurge of interest in the analysis of the possible elec- tromagnetic interference (EMI) since they are often sources of unintentional radiated emission which can alter the EMC performance of real PCBs. Especially, in presence of an RLC- circuit, high-speed signals routed on the board may carry over resonances. These resonances tend, on their own, to carry interferences over much longer distances, which can not be predicted by field or gavanic coupling. The behavior of the reradiated field, with the PCB radar cross section (RCS) being the main parameter of interest, is therefore a good figure of merit in diagnosing radiation problems on the board. This paper addresses these particular points. Especially, it provides a rigorous approach to predict radiation from PCBs in a Giagahertz transverse electromagnetic (GTEM) cell. The analysis is based upon the use of the reciprocity theorem in combination with the application of the method of moment (MoM) to the scattered field yielding a generalized impedance matrix, whose determinant represents the characteristic poly- nomial of the scattering systems. After deriving an expression for the RCS in the next section, the generalized impedance matrix is evaluated for arbitrar- ily shaped wire radiating elements with a conducting plane reflector (section III). The real-axis method characterized by Sommerfeld-type integrals and moment-method solutions (1)- (3) is used to calculate elements of the impedance matrices. The effectiveness of the method is demonstrated by inves- tigating some canonical circuit configurations and structures illustrating sources of fundamental EMI mechanism (section IV). The validity and the accuracy of the analysis become ob- vious in view of the one to one correlation with measurements (section V).

Our team at Integrity Applications Inc. (IAI) has worked extensively on radar cross-section (RCS) measurements and predictions and problems related to removal of background contamination, defect detection and localization, image editing and reconstruction (IER), sub-Nyquist interpolation, and near field-to-far field transformation (among others). In all cases, we have found that model-based optimization techniques using an l 1 minimization solver provide significantly improved performance with forward models as simple as isotropic point scatterers and as complex as rigorous method of moments (MoM) codes. In this overview paper, we present two simulated examples of model-based optimization using l 1 minimization from each end of that spectrum. The first involves the use of a sparsely-sampled set of RCS measurements to reduce the uncertainty in a MoM model due to unknown defects on the target. The model is then used to interpolate the sparsely-sampled RCS pattern data. The second involves the use of a dictionary of point scatterers and other linear basis functions to reduce the uncertainty in a set of RCS measurements due to additive contamination from clutter and noise.

Carbon fiber assisted glass fabric composite materials for broadband radar cross section reduction

In this paper, a study on the optimization of fuzzy classifier using radar cross section(RCS) values is presented to classify shell- shaped targets. Method of moments(MOM) is exploited to construct RCS database of generic shell-shaped targets in uniform angular intervals. Relative orientations are estimated from various flight scenarios of shell-shaped targets, and associated RCS values are inter-polated from the generated RCS database with uniform angular intervals. Initial membership functions are determined using the inter-polated RCS values, and particle swarm optimization(PSO) is utilized to optimize the membership functions of the fuzzy classifier in terms of probability of correct classification.Key words: Classification, Fuzzy, RCS, PSO]$ 2013^4LIG_1` $ C `78$ abc.d e fg-hij@fhg(Department of Electrical Engineering, Pohang University of Science and Technology) *LIG_1`(LIGNEX1) Manuscript received December 12, 2013 ; Revised January 13, 2014 ; Accepted February 10, 2014. (ID No. 20131212-127)Corresponding Author: Kyung-Tae Kim (e-mail: kkt@postech.ac.kr)

Reconstruction of unknown objects requires efficient inversion for measured electromagnetic scattering data. In frequency-domain integral equation method for reconstructing dielectric objects, the volume integral equations (VIEs) are involved because the imaging domain with both true unknown objects and part of background is inhomogeneous. When solving the forward scattering integral equation (FSIE), the Nyström method is used since the traditional method of moments (MoM) with the Schaubert-Wilton-Glisson (SWG) basis function may not be convenient due to the inhomogeneity of the imaging domain. The benefits of the Nyström method include the simple implementation without using any basis and testing functions and lower requirement on geometrical discretization, so it is very suitable for inhomogeneous problems. When solving the inverse scattering integral equation (ISIE), the Gauss-Newton minimization approach (GNMA) with a multiplicative regularization method (MRM) is employed. Numerical examples for reconstructing three-dimensional dielectric objects are presented to illustrate the inversion approach.

In this article, a water-based metasurface for antenna radar cross section (RCS) reduction is proposed for the first time. The metasurface has a two-layer structure of metal patch and structural water and achieves more than 9 dB RCS reduction in the super high-frequency (SHF) band from 10.6 to 26 GHz based on the mechanism of phase cancellation and wave absorption. Low scattering characteristics are achieved in the X-, Ku-, and K-bands. By using the metasurface as a radiator and introducing a feed structure, a low-scattering antenna in the C-band can be obtained. The impedance bandwidth of the antenna is from 5.7 to 6.07 GHz. The proposed antenna has an extremely small size and low profile, high aperture efficiency, and directional high gain radiation characteristics. Additionally, it exhibits low scattering across a broad frequency band. This work verifies the feasibility of water-based metasurfaces for antenna RCS reduction.

We present scattering computations performed with a newly developed stable hybridization of the finite element method (FEM) and the finite-difference time-domain (FDTD) scheme, which is based on Nitsche's method. This hybrid has not been tested on scattering problems previously, and here we compute the radar cross-section (RCS) for three different targets: (i) the perfect electric conducting (PEC) sphere, (ii) the NASA almond, and (iii) a generic aircraft called RUND. In order to assess the discretization errors associated with the hybrid, we provide comparisons with established results and techniques: (i) the Mie-series for the PEC sphere, (ii) the method of moments (MoM) implemented in the commercial code FEKO, and (iii) a stable FEM–FDTD hybrid that exploits pyramids and a curl-conforming representation of the electric field. The bistatic RCS for the PEC sphere shows second order convergence towards the analytical solution and a relative error of 2% is achieved for about 20 points per wavelength. The NASA almond has a low monostatic RCS in its horizontal plane, which makes it a good benchmark problem for scattering computations. It features a sharp tip and, as a consequence, the order of convergence for the RCS is lowered. Given a careful convergence study for the NASA almond, we achieve a highly accurate monostatic RCS by means of extrapolation and this result is state-of-the-art in the open literature.

An efficient method for simulating electromagnetic scattering from a dielectric rough surface over a frequency band is proposed in this paper. This method is based on Chebyshev series and Maehly approximation. The tapered plane wave is chosen as the incident wave to avoid the artificial edge diffraction due to the finite length of the simulated rough surface. The Gaussian rough surface is considered. Good agreements between the Maehly approximation and the exact results obtained by the method of moment (MoM) are exhibited. And the Maehly approximation is superior in the CPU time.

Aiming at the problem of thin bed recognition in the thin interbed reservoir of the middle-shallow strata in the Songliao Basin, the broad frequency band and ultra high resolution seismic processing technique is studied. After the technique being applied in 3D seismic area of Zhaoyuan in the northern part of Songliao Basin, the seismic resolution increases 2-3 times compared with conventional seismic. It is known that characteristic of AVF is existed in seismic reflection through analyzing broad frequency band and high resolution seismic data and understanding characteristic of amplitude and frequency tuning effect of which originates from thin bed reservoir seismic reflection wave, two methods are given. One is that thickness of thin bed reservoir is calculated by AVF analysis, the other is that the distribution of thin bed reservoir is predicted by using proper broad frequency band and high resolution seismic. Through the fine contrast between seismic and wells data, the top and bottom interface of the F-2 pay zone are made sure. According to the results of seismic interpretation, the technique of seismic attributes extraction along stratum interface and 3D visualization technique are used to predict the horizontal distribution of reservoir on the F-2 pay zone. Taking the prediction result as basis, the applications on optimizing the location of the exploration wells, optimizing the zone of production test and analyzing the continuity of pay zone between the production wells are studied. They demonstrate the advantage of the high resolution seismic in the thin interbed reservoir prediction and the seismic recognition of lithologic reservoir.