Scattering from composite laminate strips

An analytical model is developed for a composite laminate consisting of unidirectional fibers embedded in a dielectric slab on a conducting strip. The physics of the problem is formulated in terms of integral equations solved by the method of moments using an entire-domain Galerkin formulation. The effect of fiber spacing, the proximity of the ground plane, and the properties of the embedding dielectric are examined in relation to the nonspecular scattering characteristics of the laminate. Results of this analysis are presented for various limiting cases and are compared with experimental data     

Hybrid solutions for large-impedance coated bodies of revolution

Electromagnetic scattering solutions are developed for coated perfectly conducting bodies of revolution (BOR) that satisfy the impedance boundary condition. The integral equation arising from the impedance (Leontovich) boundary condition is solved by use of the method of moments (MM) technique along with an Ansatz for the surface currents that is derived from physical optics (PO) and the Fock theory that is modified for imperfectly conducting surfaces. The MM solution is expressed in terms of two integral (Galerkin) operators. The form of the Galerkin expansion used results in a symmetric MM system matrix. The hybrid solution is specialized for BOR's although the approach is applicable to a broader class of scatterers as well. The results are compared with the Mie solution for penetrable spherical scatterers, which satisfy the impedance boundary condition, and with recently published MM solutions for nonspherical scatterers.     

Combined field integral equation formulation for scattering by dielectrically coated conducting bodies

The combined field integral equation (CFIE) formulation for electromagnetic scattering from perfectly conducting bodies is generalized to treat conductors with layered dielectric coatings. The generalized formulation is proved to provide unique solutions at all frequencies. The method of moments is used to solve the resulting system of integral equations. Solutions in terms of two integral operators are developed for body of revolution configurations. The behavior and properties of the generalized combined field formulation are illustrated with results of calculations for coated spheres, cylinders, and cones.     

Mixed-domain Galerkin expansions in scattering problems

Entire-domain Galerkin expansions provide a computationally efficient representation in method-of-moments (MM) solutions for electrically extended surfaces forming part of a separable coordinate geometry. For surfaces not conforming to such geometries, such as those with discontinuities, subdomain representations have been used. For many classes of scattering problems involving electrically large two-dimensional scatterers with localized discontinuities, a mixed-domain Galerkin expansion is shown to lead to a computationally efficient formulation. Electromagnetic-scattering solutions are developed for such configurations. Convergence of these solutions is illustrated with choices of mixed-domain expansions as a function of surface discontinuity. The computed results are given for both transverse magnetic (TM) and transverse electric (TE) polarization and are compared with published results     

Effect of rotational invariance on the monostatic characteristics of matched bodies

It is shown analytically and numerically that a matched epsilon = mu reciprocal object with rotational symmetry will not produce any backscattering when illuminated along the axis of symmetry unless the body is invariant un der a rotation by 180 degrees. The purpose of this work is to generalize the monostatic theorem of Weston to arbitrary rotational symmetry, thereby providing a basic rule for scattering by complex bodies. The theory is illustrated by application to a few selected scatterers.     

Formulation for wire radiators on bodies of translation with and without end caps

A formulation, based on the method of moments (MM), is presented for active and passive wire radiators attached to, or near, a broad class of bodies and surfaces, including open or closed cylinders of arbitrary cross section as well as finite flat or curved panels. The development expands the utility of the MM theory for various antenna problems. The analysis incorporates a special junction basis set for the antenna attachment points. Total domain and piecewise continuous expansion functions are used on the surfaces. The formulation is primarily intended for prediction of radiation patterns of wire antennas (such as monopoles and loops) on asymmetric bodies of translation, open or closed (capped). The present method has shown satisfactory agreement with published data in the prediction of antenna input impedances as well.     

Radiation and scattering from asymmetrically excited bodies of revolution

The method of moments (MM) technique is used to compute the radiation and scattering from asymmetrically excited perfectly conducting bodies of revolution. The numerically calculated results are experimentally validated for a cone-sphere from 1 to 3 GHz. The pitch-plane radiation patterns of a cone-sphere for multiple excitation, including the effects of antenna phasing and location, are also computed.     

Electromagnetic scattering from electrically large coated flat and curved strips: Entire domain Galerkin formulation

Efficient numerical solutions are presented for electromagnetic scattering for classes of electrically large, coated, perfectly conducting strips which are flat or curved. The formulation is based on the solution of a coupled system of electric- and magnetic-field integral equations using the method of moments (MM). Entire domain Galerkin representations for the currents are used on the surface of the coating and at the coating-conductor interface. The resulting symmetric matrix equation is well conditioned and admits rapid, accurate solutions. Numerical results are presented for various coating thicknesses, strip widths, and curvatures for the transverse electric (TE) and transverse magnetic (TM) cases. The convergence of the Galerkin solution is examined as a function of these parameters. The effect of the edge approximation on the choice of expansion functions is discussed. The numerical results are compared with experimental measurements.     

Scattering from irregular-edged planar and curved surfaces

An electric field integral equation (EFIE) formulation is used to describe the electromagnetic scattering from finite planar and curved perfect electrical conducting surfaces truncated by an irregular edge. The edge can have an arbitrary form if it satisfies certain differentiability requirements. Similarly, the generating curve describing the surface can be convex, concave, or a combination of both. An edge-dependent entire domain Galerkin expansion is used for the current variation along the surface in the direction of translation. A subdomain expansion is used along the orthogonal direction. The backscatter cross sections obtained from the method of moments are compared with experimental data     

Electromagnetic scattering from extended wires and two- and three-dimensional surfaces

Efficient numerical solutions for the electromagnetic scattering for classes of electrically large one-, two-, and three-dimensional perfectly conducting scatterers are presented. The formulation is based on solution of the electric field integral equation (EFIE) using the method of moments (MM). An entire domain Galerkin representation is used for wires and two-dimensional surfaces and a combination of entire and subdomain representations is applied to surfaces in three dimensions. The analysis is extendable to corrugated surfaces formed from sections of surfaces of translation or rotation. Numerical results are presented for wires, infinite strips, and finite strips (or plates). The behavior of the solutions with the number of terms in the entire domain expansion is examined. The reconstruction of the traveling-wave contribution to the scattering cross section using various approximations is discussed, and representative examples are given.