Analysis of two-dimensional electromagnetic scattering fromnonplanar periodic surfaces using a strip current model

A method-of-moments solution is presented for the problem of two-dimensional transverse magnetic (TM) scattering of a plane wave from a nonplanar periodic surface separating two contrasting homogeneous media. The moment solution uses fictitious spatially periodic and properly modulated electric current strips to simulate the field scattered by the surface and the field penetrating the surface. The fields radiated by the current strips are represented in terms of Floquet modes, and the problem is reduced to a consideration of the fields over a single period. The simulated fields are forced to obey the continuity conditions for the tangential components of the electric and magnetic fields at a selected set of points on the interface within a single period. The procedure is simple to implement, rapidly converging, and applicable to arbitrary smooth profiles. Perfectly conducting media are treated as reduced cases of the general procedure for penetrable media. Results for sinusoidal surfaces are given and compared with available data. The efficiency of the method is demonstrated     

Scattering from periodic arrays of cylinders by Dirichlet-to-Neumann maps

A simple and efficient numerical method for computing the transmission and reflection spectra of periodic arrays of cylinders is developed. For each unit cell containing a cylinder, only the wave field on the edges of the unit cell is computed. For multilayered structures, a marching scheme based on a pair of operators is developed.     

Analysis of electromagnetic scattering from dielectric cylinders using a multifilament current model

A moment solution is presented for the problem of transverse magnetic (TM) scattering from homogeneous dielectric cylinders. The moment solution uses fictitious filamentary currents to simulate both the field scattered by the cylinder and the field inside the cylinder and in turn point-matches the continuity conditions for the tangential components of the electric and magnetic fields across the cylinder surface. The procedure is simple to execute and is general in that cylinders of arbitrary shape and complex permittivity can be handled effectively. Metallic cylinders are treated as reduced cases of the general procedure. Results are given and compared with available analytic solutions, which demonstrate the very good performance of the procedure.     

Analysis of electromagnetic scattering using arrays of fictitioussources

The use of models of fictitious elemental current sources, located inside the scatterer to simulate the scattered field, has proved to be an efficient computational technique for analyzing scattering by metallic bodies. This paper presents a novel modification of the technique in which the omnidirectional elemental sources are arranged in groups of array sources with directional radiation patterns, and the boundary testing points are arranged in groups of testing arrays with directional receiving patterns. This modification which is motivated by physical understanding is equivalent to mathematical basis transformations. It renders the system matrix more localized and thereby enables the analysis of larger bodies. The new approach is applied to the case of TM scattering by a perfectly conducting square cylinder with side-length of 20λ. Reduction of 50% in the number of the nonzero elements of the system matrix is achieved with virtually no degradation in the accuracy of the radar cross section (RCS) calculations     

Analysis and element pattern design of periodic arrays of circular apertures on conducting cylinders

The analysis and the design of elements for a large array of circular apertures on a triangular grid is approached by modeling the antenna as an infinite structure rotationally symmetric and periodic along the cylinder axis. Because of this particular symmetry, every possible excitation is the superposition, with suitable weights, of a set of fundamental excitations having uniform magnitude and linear phase progression in the azimuthal direction and in the direction of the cylinder axis ("eigenexcitations"). Thus by invoking superposition, the electromagnetic analysis of the array is reduced to the solutions of the simpler boundary value problems pertinent to the set of eigenexcitations. This is done by expanding the field in normal modes in the region exterior to the cylinder and in the waveguides feeding the apertures, followed by a field matching at the cylinder surface (obtained approximately through Galerkin's method). The realized gain pattern of the radiators can be modified to a considerable extent by using an "element pattern shaping network" (in the radiator waveguides), serving the purpose of matching the array for a selected eigenexcitation. Criteria for the network design are given. A series of numerical examples illustrate the technique and shows that a "flat" element pattern can be thus obtained with a gain falloff with respect to the peak of less than 6 dB at 80 degrees, and an increase of 2 to 3 dB in the gain at 80 degrees with respect to that obtained for the same elements matched at broadside.     

Two-dimensional scattering of a Gaussian beam by a periodic array of circular cylinders

The two-dimensional scattering of a Gaussian beam by a periodic array of circular cylinders is studied. The incident Gaussian beam is expressed as a superposition of plane waves of different amplitudes and different incident angles, using the plane-wave spectrum technique based on Fourier optics. For each plane wave, the scattered field is calculated with the T-matrix of an isolated circular cylinder and its lattice sums characterizing a periodic arrangement of the circular cylinders. The circular cylinders may be perfect conductors, dielectric or gyrotropic cylinders, as long as their T-matrices are known.     

Boundary element method for electromagnetic scattering from cylinders

The computation of low frequency scattering of electromagnetic fields by solid/hollow dielectric or conducting cylinders using the boundary element method (BEM) is considered. A general computer program has been developed for both transverse electric and magnetic cases. Numerical examples are given for conducting circular cylinders, and solid and hollow dielectric cylinders. The computational accuracy is checked by comparing the results with the analytic solution or computing an error defined from the optical theorem. In addition some problems at an interior resonance of the scatterer are discussed. The method can be directly applied to more complicated geometries.     

Transient scattering from two-dimensional dielectric cylinders ofarbitrary shape

The problem of transient scattering by arbitrarily shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time technique. The dielectric problem is approached via the surface equivalence principle. Two coupled integral equations are derived by enforcing the continuity of the electric and magnetic fields which are solved by using the method of moments. Numerical results are presented for two cross sections, viz. a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution     

Analysis of electromagnetic scattering from dielectrically coatedconducting cylinders using a multifilament current model

A method of moments solution is presented for the problem of transverse magnetic scattering from dielectrically coated conducting cylinders. The solution uses fictitious filamentary electric sources of yet unknown currents to simulate both the field scattered by the cylinder and the field inside the dielectric coating. The simulated fields obey the boundary conditions, namely, the continuity of the tangential components of the electric and magnetic fields across the air-dielectric interface and the vanishing of the tangential component of the electric field at the perfect conductor, at selected sets of points on these respective surfaces. The result is a matrix equation that is readily solved for the unknown current. The currents can be used to determine approximate values for the fields and field-related parameters of interest. The procedure is simple to implement and is general in that cylinders of smooth but otherwise arbitrary shape and coating of arbitrary complex permittivity can be handled. Illustrative examples are considered and compared with available data, demonstrating the efficiency of the solution     

Implementation of a forward-backward procedure for the fast analysis of electromagnetic radiation/scattering from two-dimensional large phased arrays

Forward-backward method (FBM) was successfully developed for the analysis of electromagnetic radiation/scattering from one-dimensional (1-D) phased array in an efficiency appealing fashion. The FBM applications to treat 2-D array problems are developed in this paper. Acceleration algorithm, performing better than the novel spectrum acceleration algorithm used for 1-D FBM computation, is also developed for this 2-D FBM so the unique advantages of high efficiency and O(N/sub tot/) computational complexity as in the 1-D problems can be retained where N/sub tot/ is the total number of array element. Numerical examples are presented to demonstrate its validity.     

Analysis of circular waveguide arrays on cylinders

An analysis is given of the mutual coupling effects in a finite array antenna of circular waveguide elements on a conducting cylinder. The array is described in terms of a scattering matrix and the multimode aperture fields of the elements are solved for by moment methods. Mutual coupling through wave propagation along the surface is treated according to GTD, since for most cases of interest the surface curvature is small in terms of wavelength. Appropriate asymptotic expansions for the magnetic field Green's function are derived for the two basic cases of an axial and a circumferential magnetic current element on the cylinder, the latter being a new case. The method, which allows the array elements to be nonuniformly spaced, applies to cylinders with radii>2lambdaand thus also includes planar arrays. Illustrative numerical examples and comparisons with infinite cylindrical and planar arrays are included.     

Surface integral representations for electromagnetic scattering from dielectric cylinders

The surface integral representations are derived for electromagnetic wave scattering from dielectric bodies. Several kinds of integral equations are given for dielectric cylinders immersed in an obliquely incident wave. The interior resonant solutions, the cause of erroneous solutions, accompanied with the equations presented here and the removal of these solutions are briefly discussed.     

Electromagnetic scattering from anisotropic plasma-coated perfect electromagnetic conductor cylinders

The scattering of electromagnetic waves by a perfect electromagnetic conductor (PEMC) cylinder coated with a homogeneous plasma anisotropic material is studied in this paper. Both of the transverse electric and the transverse magnetic polarizations of the incident waves have been analyzed and formulated. The presented analysis and formulations are general for any perfect conductor cylinder (PEC, PMC, or PEMC) with general isotropic/anisotropic material coatings that include plasma and metamaterials. The co-polarized and the cross-polarized components of the scattered fields are computed for different cases of the anisotropic plasma coated PEMC cylinders and for an anisotropic plasma column. Bistatic echo widths for the cases of PEMC, PEC (perfect electric conductor) and PMC (perfect magnetic conductor) cores have been computed and compared. The behavior of the monostatic echo width with the variation of the admittance parameter for the co-polarized and the cross polarized fields is also investigated. The comparisons of the computed results of the presented formulations with the published results of some special cases confirm the accuracy of the presented analysis.     

RESEARCH ON ELECTROMAGNETIC SCATTERING FROM PARTIALLY COATED CONDUCTING CYLINDERS

In this paper,moment methods are applied to solving the electromagnetic scatteringproblems(for both E-and H-polarizations)involving partially coated conducting cylinders.Thecomputer programs have been compiled for general use.They can be used to solve the electro-magnetic scattering from uncoated,partially coated or entirely coated cylinders of arbitrary crosssectional shape.Numerical examples are also presented to show the validity and versatility of themethod.     

A generalized scattering matrix method using the method of momentsfor electromagnetic analysis of multilayered structures inwaveguide

The method of moments (MoM) in conjunction with the generalized scattering matrix (GSM) approach is proposed to analyze transverse multilayered structures in a metal waveguide. The formulation incorporates ports as an integral part of the GSM formulation, thus, the resulting model can be integrated with circuit analysis. The proposed technique permits the modeling of interactive discontinuities due to the consideration of a large number of modes in the cascade. The GSM-MoM method can be successfully applied to the investigation of a variety of shielded multilayered structures, iris coupled filters, determining the input impedance of probe excited waveguides, and of waveguide-based spatial power combiners     

Finite element analysis of electromagnetic scattering frominhomogeneous cylinders at oblique incidence

The method of weighted residuals is used for the derivation of a convenient weak statement that is utilized for a finite-element solution of the boundary value problem for the time-harmonic electromagnetic scattering from linear, isotropic, composite cylinders at oblique incidence. The weighted-residual statement of the problem involves the z components of the electric and magnetic field and is such that the continuity of the tangential electric and magnetic fields at media interfaces is directly enforced. The finite-element solution is carried out using the bymoment method. Numerical results for echo widths and field distributions within cylinders of various shapes and compositions are presented. Comparisons of some of the results with those obtained from exact eigenfunction expansion and integral equation solutions demonstrate the validity of the method and the associated computer program     

Analysis of scattering from cylinders with a periodicallycorrugated periphery using a current-model technique

A novel solution is presented for the problem of two-dimensional electromagnetic scattering from a circular cylinder with periodically corrugated circumference. The application of the Floquet formalism is effected by representing the incident field as a sum of fields, each one obeying a Floquet periodicity condition involving a different phase factor. Respective sets of fictitious sources, comprising rotationally periodic and properly phase-modulated electric current distributions, are used to simulate the scattered field and the field in the cylinder region. Spectral and spatial formulations are presented. The solution procedure is simple to implement and is applicable to cylinders with corrugations of arbitrary profile. The accuracy of the method has been demonstrated. It has also been shown that in the limiting case of low corrugation the results of the numerical solution agree with results obtained by an approximate analytic solution     

Numerical analysis of electromagnetic scattering by electricallylarge objects using spatial decomposition technique

Apparent computational difficulties with the direct integral equation and method of moments have prompted an alternative numerical solution procedure based on the spatial decomposition technique. Using rigorous electromagnetic equivalence, the spatial decomposition technique virtually divides an electrically large object into a multiplicity of subzones. It permits the maximum size of the method of moments system matrix that needs to be inverted to be strictly limited, regardless of the electrical size of the large scattering object being modeled. The requirement on the computer resources is O(N ), where N is the number of spatial subzones and each subzone is electrically small, spanning on the order of a few wavelengths. Numerical examples are reported along with comparative data and relative error estimation to expose the applicability and limitations of the spatial decomposition technique for the two-dimensional scattering study of electrically large conducting and dielectric objects     

Finite element analysis of electromagnetic scattering from periodic cylindrical structures at oblique incidence

A hybrid technique which combines the finite element method (FEM) and an expansion of the field in terms of Floquet modes is presented for the analysis of the scattering from, and the transmission through, penetrable periodic cylindrical structures, at skew incidence. The method is very flexible and allows the analysis of practical cylindrical configurations with arbitrary cross-section and material properties.<>     

Modeling of arbitrary cross-sectional cylinder using N circular cylinders for the scattering calculations

Exact solution of the electromagnetic wave scattering by N dielectric cylinders is presented by using matrix formulation. To check this present method, two comparisons between exact solutions for a single circular conducting and dielectric cylinder and this model composed of N=25 circular cylinders are made. Numerical results of conducting and dielectric square cylinder has been also checked with well-known result (B.E.M). The scattering patterns and the near field distributions in space are presented for the concave, convex and dielectric circular cylinder with conducting reflector.