Excitation of surface waves on a unidirectionally conducting screen by a phased line source

The excitation of surface waves on a unidirectionally conducting screen produced by a phased line source located above the screen and perpendicular to the wire elements is considered. The screen consists of an infinite number of straight, perfectly conducting, parallel wires and conducts only in the direction of the wire elements. The phased line source consists of a periodic line current with an electric charge distributed along its length. The complete electromagnetic field is determined exactly and simple expressions are given for the scattered far field. It is shown that surface waves exist and simple expressions for the amplitudes are given. Another principal result is the determination of the magnitude of the complex Poynting vector for the radiated power. It is found that the pattern function lies on a cone independent of the presence of the screen and that the cone angle depends only on the phasing of the source. The pattern function at points below the screen is independent of the location of the source above the screen. Furthermore, the pattern function vanishes in the direction of the screen and this seems concomittant to the existence of surface waves. Two pattern functions are drawn for typical cases of interest. The power propagated by the surface waves is also determined. The method employed to solve the problem is based on the deduction that the scattered magnetic field component in the direction of the wire elements is zero. A consequence of this deduction is that the electromagnetic field can be derived from a single scalar wave function that satisfies a partial differential equation in the plane of the screen and a jump condition across the screen. This method is quite general and can be applied to a large class of interesting propagation problems arising from different types of excitation. The scattered far field is obtained using another method that is algebraic in character and does not require a complete solution of the problem.     

Plane wave diffraction by a thin dielectric half-plane

Expressions that apply for all observation points are derived for the field produced by a plane wave incident on a thin dielectric half-plane when the electric vector of the incident wave is parallel to the edge. Away from shadow boundaries the total field comprises an edge wave and a surface wave in addition to the transmitted and reflected waves of geometrical optics. The nature of the edge wave differs from that of a perfectly conducting half-plane in that both the amplitude and phase vary with the observation angle, for a given angle of incidence.     

Scattering by a moving unidirectionally conducting screen

The problem of scattering that results when an arbitrary field is incident on a unidirectionally conducting screen undergoing translational motion is analyzed. The screen is assumed to move at a constant speed in its own plane and in a direction perpendicular to that of conduction. A relativistically exact solution is obtained in the (stationary) frame of the observer via representing the screen as a plane where boundary conditions must be met plus a field constraint to be applied everywhere. The solution is presented in integral form and applied to the case of plane wave incidence for which low velocity effects are displayed     

Diffraction by arbitrary cross-sectional semi-infinite conductor

This paper investigates the problem of diffraction of an electromagnetic wave by a semi-infinite conductor by means of the computer method based on an integral equation formulation. The cross section of the conductor can have an arbitrary shape, provided the face shined by the incident wave is a uniform plane in the region far from the edge. In that plane region, the problem is simply that of reflection from a conductor wall for which a solution is known. This known part of the solution is analytically excluded to derive an integral equation describing the edge effect over a limited region. The limited region is unknown at first and must be determined from the results of some numerical computations. As a numerical example, a thick half-plane conductor is treated in which the electric field polarization is parallel to the conductor, i.e., the case of an incidentEwave.     

Asymptotic analysis of edge-excited currents on a convex face of aperfectly conducting wedge under overlapping penumbra region conditions

The edge-excited surface currents on a convex face of a perfectly conducting curved wedge are investigated in the asymptotic high-frequency limit for the case where the penumbra regions of the edge and surface diffractions overlap. The edge of the wedge is assumed straight, and the incident electromagnetic wave locally plane and normal to the edge. Both polarizations are considered. The surface field induced by the edge diffraction is synthesized in the spirit of the spectral theory of diffraction (STD): the solution for the edge-diffracted field is interpreted as a spectrum of inhomogeneous plane waves, and the surface field excited by each spectral plane wave is obtained by analytical continuation of the Fock (1965) functions into complex space. The main purpose of this work is to prove the reciprocity of a solution deduced previously for the problem of line source radiation from the wedge in question. As a by-product, useful identities for an incomplete Airy function and an Airy-Fresnel integral are developed     

Nonuniform Layer Model of a Millimeter-Wave Phase Shifter

The electromagnetic wave propagation of millimeter waves in dielectric waveguides with thin surface plasma layers is characterized. The phase and attenuation of a 94-GHz wave are computed for various surface plasma layer thicknesses as a function of earner density levels. The electron/hole pairs generated in the vicinity of the dielectric waveguide surface by photo excitation are assumed to have an exponential profile due to either carrier diffusion or the exponential absorption of the optical field. Field computations made for a uniform plasma layer are compared with those of the nonuniform plasma to illustrate the effects of the exponential tails of the carrier profiles on both the phase and attenuation of the millimeter wave. The thin plasma layers slightly affect the field profile of the transverse electric modes (fields polarized parallel to the plasma layer). The transverse magnetic fields are highly distorted at plasma densities greater than 10/sup 16/ cm/sup -3/.     

Guidance of waves by a moving unidirectionally conducting screen

The scattering problem for a moving, unidirectionally conducting screen excited by a conical wave is analyzed using the exact relativistic integral representation previously derived by the author (see ibid., vol.37, no.1, p.64-70, Jan. 1989). The screen is in uniform motion in its own plane and in a direction perpendicular to that of conduction. The screen is found to respond with a conical scattered field and a certain type of surface waves which are of a different nature from that which a stationary screen allows. An equivalent image source is found, and low-velocity effects are show explicitly     

Integral equation for scattering by a dielectric

The determination of the scattered and transmitted transient electromagnetic waves produced by a uniform dielectric body is reduced to the solution of a singular integral equation of the first kind for one tangential vector field defined on the surface. All derivations are carried out within the heuristic approach to Green functions and delta functions. The electric and magnetic fields are expressed in terms of the sources, initial values, and the boundary values by means of the Green function for the scalar wave equation. The appropriate integral equation is derived, and the integrals for the scattered and transmitted fields are given. The simpler problem of scattering of scalar waves is developed first. Formulas for the scattering of monochromatic fields are also given in the scalar and electromagnetic cases when transmitted fields do not vanish.     

Scattering of TE-polarized EM wave by discontinuity in groundeddielectric layer

The two-dimensional problem of EM wave interaction with a dielectric discontinuity in an infinite grounded dielectric layer is studied. An electric field integral equation (EFIE) for TE illumination has been derived based on the Green's function for the electric field produced by induced polarization currents in the discontinuity region. Impressed electric fields consist of either plane waves incident from space above the dielectric layer or surface waves supported by that layer. Method of Moments (MoM) numerical solutions for the induced electric field in the discontinuity region are implemented. The amplitudes of surface waves excited by excess discontinuity-region polarization currents are calculated, as well as the pattern of the scattered field and the associated scattering width. It is observed that the excitation of a surface-wave mode reduces the back scattered radiation for TE-polarized plane wave incidence. The accuracy of the theory is verified by comparison of numerical results with those of existing studies     

Iterative numerical computation of the electromagnetic fieldsinside weakly nonlinear infinite dielectric cylinders of arbitrary crosssections using the distorted-wave Born approximation

The electromagnetic scattering by weakly nonlinear infinite dielectric cylinders is the topic dealt with in this paper. The cylinders are assumed to be isotropic, inhomogeneous, and lossless and to have arbitrarily shaped cross sections. A time-periodic illumination of the transverse magnetic type is considered. The nonlinearity is assumed to be expressed by the dependence of the dielectric permittivity on the internal electric field, under the hypothesis that the operator responsible for the nonlinearity does not modify the scalar nature of the dielectric permittivity and produces a time-periodic output. The electromagnetic scattering is then described by an integral equation formulation, and the electromagnetic field distributions inside and outside a scatterer are approximated by an iterative numerical procedure starting with the application of the distorted-wave Born approximation. In a simplified version of the approach, the classic first-order Born approximation is used. The convergence of the approach is discussed in several examples. In the computer simulations concerning cylinders with different cross-section shapes, the effects of the nonlinearity on the field-component fundamental frequency were evaluated for different values of the nonlinear parameters in the case of a Kerr-like nonlinearity and of a uniform incident plane wave. The generation of higher-order harmonics was also considered     

Scattering of Guided Modes Caused by an Arbitrarily Shaped Broken End in a Dielectric Slab Waveguide

Electromagnetic scattering of guided modes in a dielectric slab waveguide caused by an arbitrarily shaped broken end is analyzed theoretically by using the integral equation method. By solving the integral equations iteratively, the tangential components of the electric and magnetic fields on the broken end surface are determined, from which the reflected mode power, the radiation wave power and field patterns, and the total scattered power are obtained. Numerical results are presented for the plane-perpendicular, plane-tilted, and arc-shaped end surfaces. Both TE and TM modes are assumed as an incident wave.     

Fast convergent integral equation solution of strip gratings on dielectric substrate

A fast convergent integral equation solution to the scattering problem of a transverse electric/transverse magnetic (TE/TM) plane wave by a one-dimensional periodic array of thin metal strips on a dielectric substrate is described. The formulation of the integral equation is similar to that derived by Montgomery for a two-dimensional periodic array of thin conductors on a dielectric substrate. However, the basis functions which satisfy the appropriate edge conditions are incorporated here for the unknown current expansion on the strips. Following the standard Galerkin's procedure, one may readily determine the induced currents on the strips and thus the reflected and transmitted fields. Sample numerical results are given and good agreement with previously published data is obtained. It is found that the convergence rate of this method is improved by an order of magnitude. Also it is shown that the dielectric substrate has a strong effect on the scattering from the large spacing strip grating.     

Transmission through a Conducting Screen Perforated Periodically with Apertures

A general solution to the problem of determining first the aperture field distribution and then the transmission and reflection coefficients of an infinite planar conducting sheet perforated periodically with apertures has been formulated. The excitation is considered to be a plane wave incident at any arbitrary angle. The aperture dimensions and array element spacings were assumed to be comparable with the wavelength of the incident electromagnetic field. The solution given can include the effect of a dielectric slab used to support the thin conducting sheet. The solution is obtained by matching the tangential field components at the surface of the screen. The resulting integral equation is solved by the method of moments which reduces the integral equation to a system of linear algebraic equations that can be solved with the use of a digital computer. Accurate results for both the magnitude and phase of the aperture field distribution and the transmission coefficients for the propagating modes are determined explicitly for a specific example of slots arranged in an equilateral triangular lattice. The balance of power flow between the reflected and the transmitted waves has been checked with satisfactory results. The solution can be applied to the problem of scattering from a conducting screen with periodic apertures and to the complementary problem of scattering from a set of conducting plates by the use of Babinet's principle.     

Scattering from an abruptly terminated dielectric-slab waveguide

Scattering of surface waves from an abruptly terminated dielectric-slab waveguide is investigated analytically, by means of an integral equation appropriate for the boundary-value problem of TE modes. In order to obtain a tractable solution to the equation, a Neumann Series iterative procedure is applied. Numerical results are given in several cases of abruptly ended dielectric slabs. Particular attention is directed to the behavior of electric and magnetic fields at the plane of discontinuity, since field distributions at any other region depend directly on these surface values.     

Surface Waves on an Anisotropic Plasma Sheath

A treatment of the excitation of unidirectional plane surface waves on a perfectly conducting screen covered with an anisotropic plasma sheath is given for the case in which the external magnetic field is oriented parallel to the screen but perpendicular to the direction of propagation. The dispersion relations for the surface waves and their dependence on the strength of the external magnetic field and the sheath thickness, are discussed. For sufficiently small sheath thickness, backward surface waves are found to exist. The powers carried by the surface waves and the space waves are evaluated, and the efficiency of excitation of the surface waves are determined as a function of sheath thickness for a typical set of parameters. The power carried by the forward and backward surface waves are compared for two cases in which, in a given direction, either one or both of these exist.     

Scattering from a finite array of microstrip patches

A full-wave solution to the problem of plane wave scattering by a finite array of rectangular microstrip patches printed on a grounded dielectric slab is presented. The electric field integral equation is solved using the spectral-domain Green's function/moment method approach. Derivations for the elements of the impedance and voltage matrices are presented. An efficient massively parallel computer implementation of the moment method solution is described. Computed radar cross section (RCS) data for microstrip patch antenna arrays are presented as a function of incident signal frequency and angle of incidence     

Scattering from periodic array of grounded parallel strips, TEincidence

The field distribution between strips in a periodic array of parallel strips was modeled. The electric field integral equation (EFIE) together with method of moments (MoM) was employed to solve the problem. The incident plane wave was assumed to be transverse electric (TE). The effect of the incident angle on the field between strips was investigated. For comparison, an array of the same configuration but containing a finite number of parallel strips was also modeled using the EFIE and solved via MoM. Good agreement was found even when the number of strips was small. The results are of interest for mobile radio     

Scattering by a dielectric cylinder of arbitrary cross section shape

The theory and equations are developed for the scattering pattern of a dielectric cylinder of arbitrary cross section shape. The harmonic incident wave is assumed to have its electric vector parallel with the axis of the cylinder, and the field intensities are assumed to be independent of distance along the axis. Solutions are readily obtained for inhomogeneous cylinders when the permittivity is independent of distance along the cylinder axis. Although other investigators have approximated the field within the dielectric body by the incident field, we treat the total field as an unknown function which is determined by solving a system of linear equations. In the case of the dielectric cylindrical shell of circular cross section, this technique yields results which agree accurately with the exact classical solution. Scattering patterns are also presented in graphical form for a dielectric shell of semicircular cross section, a thin homogeneous plane dielectric sheet of finite width, and an inhomogeneous plane sheet. The effects of surface-wave excitation and mutual interaction among the various portions of the dielectric shell are included automatically in this solutiom     

Scattering from multiple conducting and dielectric bodies ofarbitrary shape

A simple moment-method solution is presented for the problem of electromagnetic scattering from structures consisting of multiple perfectly conducting and dielectric bodies of arbitrary shape. The system is excited by a plane wave. The surface equivalence principle is used to replace the bodies by equivalent electric and magnetic surface currents, radiating into an unbounded medium. A set of coupled integral equations, involving the surface currents, is obtained by enforcing the boundary conditions on the tangential components of the total electric and magnetic fields. The method of moments is used to solve the integral equations. The surfaces of the bodies are approximated by planar triangular patches, and linearly varying vector functions are used for both expansion and testing functions. Some of the limitations of the method are briefly discussed. Results for the scattering cross sections are presented. The computed results are in very good agreement with the exact solutions and with published data     

Electromagnetic Fields Induced Inside Arbitrary Cylinders of Biological Tissue (Short Papers)

The electromagnetic field induced inside arbitrary cross-sectioned cylinders of biological tissue is analyzed by integral equation and moment method techniques. A TM or TE plane wave incidence is assumed, and the cylinders consist of bone or muscle and may be multiIayered. The integral equations are of the surface type, and are derived via vector Green's theorem and boundary conditions. Surface and interior fields for both a one-layer and two-layer circular cylinder are found to have excellent agreements with the exact eigenfunction expansion results, thus validating the numerical method. Extensive results are presented for arbitrary cross-section cylinders, with among these an arm model composed of an elliptical outer muscle layer and a circular bone at the center. The field plots throughout the cylinder interior thus obtained should be useful in diagnostics of microwave hazards, particularly in predictions of the so-called "hot spots."