UTD solution for electromagnetic scattering by a circular cylinderwith thin lossy coatings

A uniform geometrical theory of diffraction (UTD) solution is obtained for the field exterior to a two-dimensional circular cylinder with a thin lossy dielectric coating. The solution is convenient for engineering applications due to its simple ray format. In the lit region, the geometrical optics (GO) solution consists of the direct incident ray and the reflected ray. In the shadow region, the geometrical theory of diffraction (GTD) uses the creeping-wave format to calculate the diffracted field. In the transition regions adjacent to the shadow boundaries, where the pure ray optical solution fails, a `universal' transition integral is used for the UTD solution to calculate the field. Numerical values for the essential transition integral are deduced, by a heuristic approach, from alternative representations of the Green's function for a circular cylinder with coating. Numerical results obtained from the UTD solution show excellent agreement with the eigenfunction results for cylinders with thin dielectric coatings     

Theoretical and experimental validation of UTD applied to electromagetic-wave scattering by circular cylinders

The scattering of obliquely incident electromagnetic waves by a perfectly conducting circular cylinder is analyzed. In this paper the accuracy of a high-frequency asymptotic model based on the Uniform Theory of Diffraction (UTD) is investigated by comparing UTD simulations with results obtained from the exact eigenfunction solution for plane-wave incidence. UTD results are also compared with results from experiments carried out at 50 GHz, for various cylinder radii and for different linear wave polarizations. Excellent agreement between the measurement results and the theoretical ones is obtained.     

An absorber tip diffraction coefficient

The UTD corner diffraction solution for a perfectly conducting corner is empirically modified for the case of a dielectric corner. The dielectric may be lossless or lossy, but is assumed to be homogeneous. This modified solution is used to calculate the bistatic scattering from the tip of a dielectric pyramid. Sample calculations display some features of the scattering from a single lossy dielectric pyramid. To verify the solution, calculations are compared with backscatter measurements of a single pyramid that is cut from a homogeneous lossless dielectric (polyethylene). Calculations are then compared with measurements for the more pertinent case of bistatic scattering from a wall of pyramidal radar absorbing material     

阻抗边界圆柱散射场的UTD解

本文分析了二维阻抗圆柱的电磁散射机理，讨论了金属圆柱、有耗涂层圆柱与阻抗圆柱的等效特性，获得了它们的散射场一致性绕射理论（ＵＴＤ）解。最后，给出了一组计算实例。     

The diffraction of an inhomogeneous plane wave by an impedancewedge in a lossy medium

The diffraction of an inhomogeneous plane wave by an impedance wedge embedded in a lossy medium is analyzed. The rigorous integral representation for the field is asymptotically evaluated in the context of the uniform geometrical theory of diffraction (UTD) so that the asymptotic expressions obtained can be employed in a ray analysis of the scattering from more complex edge geometries located in a dissipative medium. Surface wave excitations at the edge and their propagation along the wedge faces are discussed with particular emphasis on the effects of losses     

Simple high frequency solution for interior fields of open-ended parallel plate waveguide

The problem of electromagnetic (EM) plane wave scattering by an open-ended, perfectly-conducting, semi-infinite two-dimensional (2-D) parallel plate waveguide with a thin uniform layer of lossy material on its inner walls is analysed using a high frequency method. The fields coupled into the waveguide from the exterior are found via the uniform geometrical theory of diffraction (UTD) ray method.<>     

Computation of Scattering from Penetrable Cylinders with Improved Numerical Efficiency

An integral-equation formulation is used to obtain numerical results for the scattered fields of a penetrable cylinder immersed in either a lossy halfspace or a lossy homogeneous medium. The cylinder is iluminated by a parallel electric line source. A set of plane waves interior to the inhomogeneity (scatterer) is used as basis functions. This results in more than an order of magnitude decrease in the computer time required to obtain numerical results for larger sized targets. Further, the integral-equation solution is extended to include the planar interface between the air and the earth. The validity of the approximate forms proposed earlier to represent the interface is reexamined.     

用MEI—FD方法分析Chiral媒质的电磁散射问题

本文应用不变性测试分程和有限差分方法分析Ｃｈｉｒａｌ媒质的电磁散射问题。应用该方法时，要在所讨论的区域内建立起一组有关电场和磁场的耦合差分方程，并且要在截断边界上应用不变性测试方程建立起有关边界点系数的方程。文中给出了一些非均匀、有耗且具有电大尺寸任意横截面Ｃｈｉｒａｌ柱的雷达散射截面的数值结果     

Scattering from a conducting cylinder above a lossy medium

Scattering from conducting objects above a lossy medium is a problem of current interest concerning the radar detection and identification of targets near the ground. Using a Green's function approach, in a way similar to that used to treat scattering from underground objects, the problem of electromagnetic scattering from conducting cylinders located above the ground is considered. The unknown surface current J(r) of the conducting cylinder is determined through the resulting integral equation and the far-field in the air is evaluated employing the steepest descent method of integration. Numerical results for the far-field region of the overground scatterer are plotted and some useful conclusions concerning the influence of the various parameters of the problem are also discussed.     

A hybrid asymptotic solution for the scattering by a pair ofparallel perfectly conducting wedges

The overlapping transition regions of the double diffraction by a pair of parallel wedge edges are considered for the hybrid case where the gap between the edges is small compared to the distances from the source and the observation point (plane-wave-far-field limit) and the scatterer as a whole is large (or infinite). A closed-form asymptotic solution for the scattered field continuous at all angles of incidence and scattering is constructed for this case. The peculiar feature of this solution is a hybrid representation of the field singly diffracted by the first wedge: a part of it is described by a nonuniform, geometrical theory of diffraction (GTD) expression, while the other part is described in terms of the uniform theory of diffraction (UTD). The rest of the diffracted ray fields are described by nonuniform expressions, with singularities mutually canceling on summation. This solution is applied to the scattering by a perfectly conducting rectangular cylinder with appropriate geometrical parameters, and agreement with moment method calculation is demonstrated     

A caustic corrected UTD solution for the fields radiated by asource on a flat plate with a curved edge

Corrections to the uniform geometrical theory of diffraction (UTD) that account for the caustics caused by the coalescence of the diffraction points on a curved edge are derived. This creates a new curvature dependent diffraction coefficient that has not been previously accounted for in the UTD. The far-zone radiation by a short monopole mounted on an elliptic disk is analyzed using this caustic corrected UTD solution. Theoretical results are verified in the principal plane by comparison with a method of moments solution. The resulting solution for the radiated field is accurate and provides useful insight into the scattering phenomena. This insight is necessary in order to obtain more general solutions     

An efficient formulation to determine the scatteringcharacteristics of a conducting body with thin magnetic coatings

Two new and efficient surface integral equations, derived from corresponding volume integral equations, are developed to calculate the scattering of electromagnetic (EM) waveform from an arbitrarily shaped conducting body coated with thin lossy magnetic film. Their numerical solutions by the method of moments (MM) for two-dimensional structures with full or partial coatings are presented. It is shown that the radar cross-section of a conducting body can be significantly reduced by coating it with a lossy magnetic film. To verify the validity and accuracy of the proposed formulation, another method based on the expansion of cylindrical harmonic functions with real arguments is also developed to calculate the scattering of a plane EM wave from an electrically large coated circular cylinder. The same problem was also solved by the proposed formulation, and excellent agreement between the two approaches was achieved. In addition, numerical results of the scattering from a rectangular coated cylinder is shown to be consistent with that obtained by a modified finite-difference-time-domain (FDTD) method     

THE ELECTROMAGNETIC SCATTERING OF A RADIALLY INHOMOGENEOUS DIELECTRIC CYLINDER

A new method is demonstrated for solving the electromagnetic scattering problemof a radially inhomogeneous lossless or lossy dielectric cylinder by Fourier series expansion.Com-pared with other methods,the method is simpler in numerical calculation and can be used forsolving scattering problems of a cylinder due to an arbitrary incident electromagnetic beam.     

A uniform geometrical theory of diffraction for an imperfectly conducting half-plane

Diffraction tensors are presented in the context of the uniform geometrical theory of diffraction (UTD) for the high frequency scattering by an impedance half-plane at normal and oblique (skew) incidence. These are based on the exact Wiener-Hopf solution and were derived according to the UTD ansatz. In addition, unlike previous uniform diffraction coefficients, the ones given here reduce to the known UTD diffraction coefficients for the perfectly conducting case. The coefficients are explicit and therefore appropriate for practical applications. Several scattering patterns are also presented and compared to a previous heuristic solution.     

电磁格点理论在有耗介质涂层导体薄片上TE波散射中的应用

在ＴＥ波入射下，对于计算二维封闭导体柱散射问题所常用的磁场积分方程法，当用于导体薄片时将会失效．本文采用电磁格点理论和电场方法研究这个问题．结合二维介质柱的电磁格点方程，解决了有耗介质涂层导体薄片的ＴＥ波散射．文中给出计算实例．     

On the accuracy of the UTD for the scattering by a cylinder

The UTD formulation for the scattering by a cylinder is valid for antennas that are removed from the cylinder surface. The usual guideline is that reliable results can be obtained for antennas that are about λ/4 or more away from the surface. By exploring a few cases, we show that λ/4 is unnecessarily large for the lit region and sometimes too small for the shadow region. In addition, we find that with a simple heuristic modification to the UTD, heights as small as λ/20 can be accommodated, with an accuracy that is sufficient for most engineering applications     

A UTD based asymptotic solution for the surface magnetic field on a source excited circular cylinder with an impedance boundary condition

An asymptotic solution based on the uniform geometrical theory of diffraction (UTD) is proposed for the canonical problem of surface field excitation on a circular cylinder with an impedance boundary condition (IBC). The radius of the cylinder and the length of the geodesic path between source and field points, both of which are located on the surface of the cylinder, are assumed to be large compared to a wavelength. Unlike the UTD based solution pertaining to a perfect electrically conducting (PEC) circular cylinder, some higher order terms and derivatives of Fock type integrals are found to be significantly important and included in the proposed solution. The solution is of practical interest in the prediction of electromagnetic compatibility (EMC) and electromagnetic interference (EMI) between conformal slot antennas on a PEC cylindrical structure with a thin material coating on which boundary conditions can be approximated by an IBC. The cylindrical structure could locally model a portion of the fuselage of an aircraft or a spacecraft, or a missile. Validity and accuracy of the numerical results obtained by this solution are demonstrated in comparison with those of an exact eigenfunction solution.     

Radiation and scattering from large polygonal cylinders, transverse electric fields

The computation of radiation and scattering of electromagnetic fields by electrically large convex conducting cylinders, using the geometrical theory of diffraction (GTD) is considered. A general computer program has been developed for the transverse electric case. Illustrative computations are made for examples of radiation from a line source of magnetic current in the vicinity of a polygonal cylinder, scattering of plane waves, radiation from slots, and radiation from electric dipoles. Also given are examples of computations for conducting strips, grazing incidence on polygonal cylinders, and scattering from small cylinders. The computational accuracy is checked by comparing the results to corresponding ones computed by a moment solution to theH-field integral equation.     

Multiple cylinder UTD solution

The uniform theory of diffraction (UTD) is extended to multiple cylinder structures by introducing a new formulation of the UTD diffraction coefficients in cooperation with a slope diffraction term for maximum accuracy in the electromagnetic modelling. The solution is, then, applicable to radiowave paths where mountains, hills or other rounded objects are the main cause of electromagnetic diffraction.     

Electromagnetic scattering by weakly lossy multilayer ellipticcylinders

The analytic solution to the electromagnetic scattering due to a multilayer elliptic cylinder is generalized to the case of weakly lossy materials by using a first-order truncation of the Taylor expansion of each Mathieu function