Electromagnetic scattering interaction between a dielectriccylinder and a slightly rough surface

An electromagnetic scattering solution for the interaction between a dielectric cylinder and a slightly rough surface is presented in this paper. Taking the advantage of a newly developed technique that utilizes the reciprocity theorem, the difficulty in formulating the secondary scattered fields from the composite target reduces to the evaluation of integrals involving the scattered fields from the cylinder and polarization currents of the rough surface induced by a plane wave. Basically, only the current distribution of isolated scatterers are needed to evaluate the interaction in the far-field region. The scattered field from the cylinder is evaluated in the near-field region using a stationary phase approximation along the cylinder axis. Also, the expressions for the polarization current induced within the top rough layer of the rough surface derived from the iterative solution of an integral equation are employed in this paper. A sensitivity analysis is performed for determining the dependency of the scattering interaction on the target parameters such as surface root mean square (RMS) height, dielectric constant, cylinder diameter, and length. It is shown that for nearly vertical cylinders, which is of interest for modeling of vegetation, the cross-polarized backscatter is mainly dominated by the scattering interaction between the cylinder and the rough surface. The accuracy of the theoretical formulation is verified by conducting polarimetric backscatter measurements from a lossy dielectric cylinder above a slightly rough surface. Excellent agreement between the theoretical prediction and experimental results is obtained     

Gaussian beam scattering from a conducting cylinder partially buried in a ground plane

The problem of scattering from an infinitely long conducting cylinder that is partially buried in a perfectly conducting ground plane due to an obliquely incident gaussian beam is solved by an exact procedure based on the method of images by first adopting a simplification originally proposed by Kozaki. The incident and the specularly reflected fields are expressed in terms of cylindrical vector wave functions multiplied by a weighting function which involves the beam parameters like the radial distance of the source and beam width. The scattered fields originating from the cylinder and its image in the ground plane are expressed in terms of cylindrical vector wave functions. The boundary conditions on the surface of the cylinder are then imposed and this procedure leads to a coupled infinite system of equations for the even and odd mode expansion coefficients of the scattered field. These equations are solved numerically for the case of cylinders having electrical radius in the Rayleigh and resonance regions. Both the transverse magnetic and transverse electric polarizations of the incident beam wave are considered and some representative numerical results for the scattered far-field are presented in graphical form. The magnitude of the induced current for the TM polarization is calculated and compared with the corresponding case of plane wave incidence.     

Current induced by TE excitation on coupled and partially buriedcylinders at the interface between two media

An analysis is described for determining the current induced by transverse electric (TE) excitation on coupled conducting cylinders near the planar interface separating two semi-infinite homogeneous half-spaces of different electromagnetic properties and on partially buried conducting cylinders. The conducting cylinders, of general cross section, are of infinite extent and the excitation is transverse electric to the cylinder axes. Coupled integral equations for the currents induced on the cylinders are formulated and numerical methods for solving them are presented. Data showing the induced current distribution for various cylinders and media parameters of interest are presented and discussed. Relative to the homogeneous space case, the presence of the two media significantly alters the current distribution, especially near the interface     

Electromagnetic diffraction from a dielectric-filled slit-cylinderenclosing a cylinder of arbitrary cross section: TM case

A simple moment solution to the problem of the diffraction of a TM plane wave from an infinite, perfectly conducting slotted cylinder of an arbitrary cross section is summarized. The slit cylinder encloses a smaller perfectly conducting cylinder of an arbitrary cross section, and the space between the cylinders is filled with a dielectric material. The equivalence principle is used to obtain a set of coupled integral equations for the induced/equivalent surface currents on the cylinders, and the method of moments is used to solve numerically the integral equations. The electric field integral equation formulation is used. The advantages and the limitations of the method are discussed. Sample results for the induced current, aperture field, internal field, and scattering cross sections are given. These are in good agreement with some of the available published data     

Scattering and Pattern Perturbation by a Conducting Tubular Cylinder of Finite Length

This paper uses the plane-wave-spectrum (PWS) scattering technique to determine the scattering and pattern-perturbation effects of a conducting tubular cylinder of a finite length situated in the neighborhood of a 2 x 4 dipole array. Both the axial and the circumferential current distributions induced on the cylinder due to a unit-magnitude incident plane wave have been calculated. Typical patterns for the scattered field and the perturbed radiation field are presented for various cylinder locations.     

Induced current in and scattered field from a finite cylinder with arbitrary conductivity and permittivity

A finite cylinder with arbitrary conductivity and permittivity is illuminated by an EM wave. The induced current in and the scattered field by the cylinder are determined based on the numerical solution of a tensor integral equation. An experiment has been conducted to verify the theory. Biological and metallic cylinders are emphasized in the study.     

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     

Current induced on a conducting cylinder located near the planar interface between two semi-infinite half-spaces

An analysis is described for determining the current induced by a known excitation on a conducting cylinder located near the planar interface between two semi-infinite, homogeneous half-spaces of different electromagnetic properties. The perfectly conducting cylinder of general cross section is of infinite extent and the excitation is transverse magnetic to the cylinder axis. An integral equations for the induced current is derived and a numerical method for solving it is developed. The kernel of the integral equation contains a term corresponding to the usual open-space Green's function plus a term proportional to a Sommerfeld-type integral in two dimensions. Various forms of the Sommerfeld-type integral are given and the choices of form amenable to efficient evaluation are discussed. For a flat strip, a circular cylinder, and a rectangular cylinder, data are presented and discussed for selected parameters. Data are presented for cylinders above and below the interface as well as for a cylinder resting on the interface.     

Polarization effects in microwave diversity imaging of perfectlyconducting cylinders

A theoretical vector development is derived for the directly and mutually scattered wavefield of two cylinders in a bistatic measuring system. The approach is first to give an expression for the field scattered from a single cylinder illuminated by a right-hand circularly polarized plane wave. This expression is then extended to the case of the directly scattered (or first-order) field of two cylinders. The mutually scattered (or second-order) field of two cylinders is then formulated in terms of a coherent summation of the scattered field from each cylinder due to the incident wave scattered from the other cylinder. In order to simplify computational tasks, only the second-order scattered field is analytically derived; this is called the mutually scattered field. The total wavefield scattered by two cylinders becomes the coherent superposition of the directly scattered component and the mutually scattered component for each polarization. The use of an automated microwave imaging facility employing frequency, polarization and angular diversity to verify the results of theoretical analysis is described. The analytical and experimental results are shown to be in good agreement. The results show that the effects of polarization state transformation or change in the mutually scattered field component are more pronounced than in the directly scattered component     

Incremental length diffraction coefficients for the shadow boundaryof a convex cylinder

Incremental length diffraction coefficients (ILDCs) are obtained for the shadow boundaries of perfectly electrically conducting (PEC) convex cylinders of general cross section. A two-step procedure is used. First, the nonuniform (NU) current in the vicinity of the shadow boundary is approximated using Fock (1965) functions. The product of the approximated current and the free-space Green's function is then integrated on a differential strip of the cylinder surface transverse to the shadow boundary to obtain the ILDCs. This integration is performed in closed form by employing quadratic polynomial approximations for the amplitude and unwrapped phase of the integrand. Examples are given of both the current approximations and the integration procedure. Finally, as an example, the scattered far field of a PEC sphere is obtained by adding the integral of the NU ILDCs of a circular cylinder along the shadow boundary of the sphere to the physical optics (PO) far field of the sphere. This correction to the PO field is shown to significantly improve upon the accuracy of the PO far-field approximation to the total scattered field of the sphere     

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.     

Electromagnetic interaction between two parallel circular cylinderson a planar interface

Multiple interaction between two parallel and infinitely long circular cylinders on a planar interface separating two different media is analyzed theoretically. The scattering equations are derived from the so-called extinction theorem applied to this particular geometry. For simplicity, the surface is considered to be perfectly conducting although the method can be extended for any material. The equations, solved numerically by means of an appropriate discretization of the surface, provide the electric surface current density from which the scattered intensity can easily be calculated. Scattering of the transversal-magnetic and transversal-electric incident wave is studied as a function of the cylinder separation for cylinder diameters from 0.2λ to 4λ (λ being the incident wavelength). The effects of the interaction between cylinders are shown in the scattering cross section and in the surface current density of the planar substrate and of the cylinders     

Combined field solution for TM scattering from multiple conducting and dielectric cylinders of arbitrary cross section

A simple moment solution is given for the problem of electromagnetic scattering from multiple conducting and dielectric cylinders of arbitrary cross section. The system of conducting and dielectric cylinders is excited by a plane-wave polarized transverse magnetic to the axis of the cylinders. The equivalence principle is used to obtain three coupled integral equations for the induced electric current on the conducting cylinders and the equivalent electric and magnetic currents on the surface of dielectric cylinders. The combined field integral equation (CFIE) formulation is used. Sample numerical results are presented. The agreement with available published data is excellent.     

Analysis of TE scattering from dielectric cylinders using amultifilament magnetic current model

A moment solution is presented for the problem of transverse electric (TE) scattering from homogeneous dielectric cylinders. The moment solution uses fictitious filamentary magnetic 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     

计算细理想导电圆柱RCS的物理模式基矩量法

根据GTD—MOM技术给出一种物理模式基的概念 ,并用之分析细理想导电圆柱的电磁散射 ,求解其雷达散射截面积 (RCS)。圆柱表面上的电流假设由三部分组成 :入射波的感应电流和圆柱两端的反射电流。该方法较传统的全域基矩量法减小了计算机内存 ,加快了计算速度 ,而且数值计算结果与全域基的结果吻合较好。     

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.     

Self-consistent GTD formulation for conducting cylinders with arbitrary convex cross section

A user-oriented computer program has been developed for high frequency radiation and scattering from infinitely-long perfectly. conducting convex cylinders. The analysis is based on the self-consistent geometrical theory of diffraction (GTD). The cylinder is modeled as anN-sided polygon. Two cylindrical waves with unknown amplitudes are assumed to travel in opposite directions on each face of the polygon. The boundary conditions for the corners are applied to set up a matrix equation for2Nunknowns (the amplitudes associated with the traveling cylindrical waves). Crout's method is used to solve the matrix equation. Once the amplitudes for the traveling waves are determined, the radiation or scattered field is readily obtained via the usual GTD techniques. Numerical results are presented for radiation and scattering from rectangular, semi-circular, circular, and elliptic cylinders for both principal polarizations. The results show excellent agreement with GTD, moment, and eigenfunction solutions.     

Scattering by arbitrarily cross-sectioned layered, lossy dielectric cylinders

The scattering properties of TM or TE illuminated lossy dielectric cylinders of arbitrary cross section are analyzed by the surface integral equation techniques. The surface integral equations are formulated via Maxwell's equations, Green's theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by flat-pulse expansion and point matching. Once the surface fields are found, scattered field in the far-zone and radar cross section (RCS) are readily determined. RCS thus obtained for circular homogeneous dielectric cylinders and dielectric coated conducting cylinders are found to have excellent agreements with the exact eigenfunction expansion results. Extension to arbitrary cross-sectioned cylinders are also obtained for homogeneous lossy elliptical cylinders and wedge-semicircle cross-sectioned cylinders, with and without a conducting cylinder in its center. RCS dependences on frequency and conductivity as well as the matrix stability problem of this surface integral equation method are also examined.     

Solutions of the Vector Wave Equation for Inhomogeneous Dielectric Cylinders--Scattering in Waveguide

Some solutions of the vector wave equation for an inhomogeneous dielectric cylinder, suitable for numerical calculations of the scattered electromagnetic (EM) field in waveguide, are presented in cases where the cylinder axis is parallel, or perpendicular, to the incident electric field vector. The scattered field, given in terms of normal modes of the rectangular waveguide, permits easy determination of the transmission and reflection coefficients for the structure. The dielectric susceptibility may be considered as variable along the cylinder radius according to a parabolic function (Luneberg-type profile). Finally, numerical results of the scattered near field are presented for Teflon cylinders of different diameters, in the case of parallel polarization. They are compared with laboratory measurements in the microwave X band made as a reliability test of the computational program. The agreement between measured and computed values is satisfactory within a deviation of 10 percent in the whole frequency band.     

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