Electromagnetic scattering from longitudinally corrugated cylinders

The scattering of plane electromagnetic waves from circular cross-section cylinders, longitudinally corrugated to realize anisotropic structures, is analyzed. The solution is devised at oblique incidence and for an arbitrary polarization of the incident wave using a rigorous Floquet modal expansion of the field. The implementation of the procedure is discussed with emphasis to its numerical efficiency     

High frequency scattering from polygonal impedance cylinders andstrips

An analysis is presented for the high-frequency diffraction by convex polygonal cylinders with arbitrary side impedances. The authors extend their solution for the multiply diffracted fields associated with a double wedge (see ibid., vol.36, no.5, p.664-678, 1988). The analysis thus utilizes the extended spectral ray method (ESRM) that is applicable to nonray optical regions. Diffraction coefficients yielding a uniform total field are given for up to and including all fourth-order mechanisms. An important aspect of this analysis is the rigorous and uniform incorporation of the surface-wave effects in the resulting diffraction coefficients. A general polygon computer code was written that includes up to a third-order mechanisms. Based on this code, backscatter and bistatic patterns are given for impedance cylinders with triangular and square cross sections. The results are found to be in remarkable agreement with corresponding moment method data. As a matter of completeness, uniform diffraction coefficients are presented for a strip (which is a special case of a cylinder) that can have unequal face impedances     

Electromagnetic scattering from conducting circular cylinders inthe presence of a stratified anisotropic medium-TM case

Scattering by a conducting circular cylinder in the presence of a stratified ferrite medium is investigated analytically using a combined Green's function (G-function) and integral equation approach. The incident plane wave is polarized along the axis of the cylinder. The bias DC magnetic field is in the same direction. The G-function of the structure is developed by well-known techniques of matrix analysis, and the appropriate integral equation for the electric field is derived on the basis of the modified reciprocity theorem. Its solution is followed by numerical results presented in graphical form for both the current density induced on the scatterer's surface and the scattered far field. The possibility of controlling the scattering properties of the structure by varying the degree of anisotropy is also investigated. The main conclusion is that anisotropic materials can be used to control antenna radiation characteristics     

Electromagnetic scattering from nonlinear anisotropic cylinders. I.Fundamental frequency

The solution of the problem of electromagnetic scattering of obliquely incident plane waves by homogeneous, nonlinear anisotropic cylindrical structures is obtained. The medium of the scatterer is characterized by Volterra-type integrals for the electric and magnetic flux density vectors D and B, respectively. The nonlinear problem is solved using the perturbation method. The effects of nonlinearities on the field properties both inside and outside the scatterer, together with the effect on the radar cross section, are investigated for the fundamental frequency components. To demonstrate the validity of the approach, the results obtained by the perturbation method are compared with those obtained using the plane wave representation method of D. Censor (1983), where the iteration method is used to solve the resulting dispersion equation. The results are in very good agreement in both amplitude and phase of the fields for the case of very weak nonlinearity. When the relative magnitude of the nonlinear component of the permittivity is increased, the iteration method shows a faster divergence of the phase from the linear phase     

Transient scattering from conducting cylinders

A method for determining the fields scattered by arbitrarily shaped cylindrical conducting structures with a transient incident wave is described. The transient scattering problem is reduced to the solution of a time domain integral equation which in turn is solved directly in the time domain by means of a digital computer. The approximate electromagnetic impulse response for a number of cylindrical scatterers is calculated using this method.     

Electromagnetic scattering from a corrugated wedge

The scattering of a TE-polarized wave from a perfectly conducting wedge with one of its faces loaded with cavities is considered. The proposed formulation reduces the analysis of the original problem to two simpler configurations: one concerning the geometry of the corrugation (internal problem) and one concerning the geometry of the perfectly conducting wedge (external problem). By resorting to a suitable numerical technique, it is possible to account for arbitrarily shaped corrugations filled with inhomogeneous material. Numerical results demonstrate the validity of the technique and its applicability to general shape corrugations. The analysis of corrugated horns is considered and results are shown that demonstrate the flexibility of the procedure to analyze horns with arbitrarily shaped corrugations     

High frequency scattering from an open-ended semi-infinite cylinder

A simple high-frequency asymptotic expression for the backscattered field from a semi-infinite hollow circular cylinder is derived from the exact Weiner-Hopf solution. The resultant equations are valid for both polarizations and can be easily numerically evaluated. Comparisons of the computed results and the measured data acquired through the utilization of a sub-nanosecond pulse radar system are generally good.     

Electromagnetic scattering from two adjacent cylinders

The problem of electromagnetic scattering from two adjacent cylinders is considered. The approximate analytical scattering solutions up to second order are derived for two adjacent, long finite length cylinders. The method used can avoid the complex evaluation of scattering field under nonplane wave illustrated when calculating the secondary scattering fields. The bistatic specular scattering is discussed, and the results are compared with numerical computations based on the method of moments     

Forward scattering from cylinders of triangular cross section

The induced-field ratios (IFR) of conducting cylinders of a triangular cross section have been calculated. When the width of the cross-section is in the range of 1-2 wavelengths, theE-wave IFR's are substantially less than the corresponding values for square or circular cross sections. From the standpoint of RF aperture blocking of a reflector antenna, the triangular cross section thus offers an advantageous cross section for feed-support struts.     

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     

High frequency scattering by a conducting ring

Asymptotic formulae are derived for the Fourier coefficients of the thin wire kernel in the integral equation for the electric current on an electrically large, thin circular loop. The total current induced on the ring by a plane electromagnetic wave is approximated by a modified physical optics term proportional to the incident field, plus resonant terms of lossy circulating waves. Numerical evaluation of the dominant poles and residues of the ring transfer function provides the amplitudes and complex propagation constants of these natural modes.     

Mode uncoupling in oblique scattering from radially inhomogeneous cylinders

A class of radially inhomogeneous cylindrical scatterers is given, for which the TM and TEfields produced by an obliquely incident plane wave are uncoupled.     

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.     

Application of point-matching method to scattering from quadrilateral cylinders

The possibility of constructing computer programs with the capability of generating detailed information on the scattering characteristics of a wide class of perfectly conducting cylinders of arbitrary cross-section in the `resonance? range has made further investigation of the `point-matching? technique of some interest. In the letter, the utility of the point-matching method is explored for a class of quadrilateral cylinders when the region exterior to the scatterer can be described by a set of overlapping domains within which the field can be expanded in terms of complete eigenfunction expansions.     

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.     

Bistatic scattering from a vegetative medium simulated by cylinders

By considering the vegetation as a regular homogeneous distribution of individual scatterers and thus modeling it as an array of perfectly conducting finite thin circular cylinders over a ground plane, bistatic cross section is determined using the image principle and its variation with the angle of incidence, length, and diameter is studied.     

The matrix Riccati equation for scattering from stratified chiralspheres

Angular scattering from radially stratified spherical chiral objects is investigated. Based on the principles of invariant embedding, we formulate a matrix Riccati equation that can be used to examine basic scattering properties of spherical chiral structures with radial inhomogeneities in permittivity, permeability, and chirality. High- and low-frequency limits as well as weak reflection and constant impedance cases for this equation are examined. We show that in the limit of large radii of curvature, this formulation yields the planar result