The false image of a line current within a conducting half-space

We show that the fields from a current line source, within a conducting-half-space, are only inadequately characterized by a positive real image in the air region. Such an assumption or assertion, as employed in previous electromagnetic compatibility (EMC) studies, is called into question. Buried cables are mentioned in particular     

Wire and strip conductors over a dielectric-coated conducting ordielectric half-space

The complex wavenumber and characteristic impedance are determined for a wire or flat strip over a dielectric-coated half-space that can be a conductor or a dielectric with large permittivity. Elevated microstrip is an example of the configuration. The properties of the wire as an antenna or transmission lines are determined from those of the insulated antenna with a two-layer eccentric insulation. The theory is extended to the strip conductor with the help of a comparison of the tubular and strip conductors over a perfectly conducting half-space     

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.     

Excitation of a conducting half-space by a toroidal coil

The possibility exists that a non-contacting “vertical-electrical dipole”source could be devised, to excite both horizontal and vertical currents in the subsurface. The scheme is quite simple, but it seems to have been overlooked or, at least, not disclosed, hitherto. The idea is to employ a toroidal coil carrying an alternating current, which is located in or just above the air/earth interface. As shown, when the diameter of the toroid is small compared to the distance to the observer, the effective source is effectively a vertical-electric dipole. This may be obvious to some, but the situation has some interesting complications, because of the presence of the interface. The pertinent analysis is outlined     

Maximum field criteria for a line current source in a conducting medium

Criteria are presented for the maximum amplitudes of the electric and magnetic fields that can be produced at various distances by a line current source immersed in a conducting medium of infinite extent.     

DC potential anomalies caused by a conducting body in ananisotropic conducting half-space

Image theory for dc problems involving a current source in an anisotropic half-space bounded by either a perfectly magnetically conducting (PMC) or electrically conducting (PEC) plane is being used to get the solution for the potential in integral form. A dipole approximation for a small sphere is developed     

Excitation of surface waves on a unidirectionally conducting screenby an arbitrary phased line source parallel to it

An exact solution is obtained for the scattering problem of a phased line source in front of a screen and parallel to it. The direction of perfect conduction forms an arbitrary angle Ω with the normal projections of the filament on the screen. The coupled surface waves and scattered far field are investigated, and alternative expressions suitable for numerical calculations are presented together with numerical results. It is found that the energy is highly localized in the neighborhood of the screen, and the closer the filament is to the screen, the larger the excitation of the surface wave. In addition, it was found that the surface waves travelling to the right and to the left of the filament are different and become identical only when either Ω=π/2 or the propagation constant γ=π/2. For the special cases γ=Ω and Ω+γ=π, a surface wave is excited in only one side of the screen. In general, the surface waves are slow waves which are circularly polarized with opposite polarization on both sides of the screen. The ordinary end fire source was found to be characterized by 100% launching efficiency     

Radiation of a coaxial line into a half-space

We present a new approach to the problem of radiation by a coaxial line into a half-space. We obtain boundary-integral equations for the current densities over the walls of the coax and its opening to the half-space. Using the modes of the coax for basis and testing functions, we convert the integral equations to an infinite system of linear equations, the unknowns being the coefficients of the current density expansions. We demonstrate how, by solving a small subsystem, we can obtain the fields everywhere in space.     

Theory of a vertical tubular antenna located above a conducting half-space

The input admittance and the current distribution of a finite vertical tubular dipole antenna located above an infinite dissipative half-space can be found as a function of the distance above and the electric properties of the dissipative half-space. An integral equation for the current on the surface of the antenna is formulated and subsequently solved by numerical evaluation of associated moment functions in the Fourier transform plane. The magnitude, but not the distribution, of the current is found to be strongly affected by the presence of the dissipative medium. At certain distances above the half-space, the input conductance of the antenna reaches its maximum value.     

Solving the current element problem over lossy half-space without Sommerfeld integrals

An approach is presented for efficient computation of the vector potentials arising in the problem of a current element radiating over a lossy half-space. The present approach departs from the conventional ones in that it works primarily with the transform domain representations rather than with the Sommerfeld integrals which are the corresponding spatial domain counterparts. The key step in the present method is to approximate the transforms using a suitable approximation which is valid for a wide range of parameters of practical interest. The approximated transforms can be inverted in a closed form for the horizontal component of the vector potentials (Pi_{z}) and can be expressed in a computationally efficient form for the vertical component (Pi_{z}). Numerical results illustrating the accuracy of the method are presented and some estimates of comparative computational times are also included.     

High-frequency fields excited by a line source located on a perfectly conducting concave cylindrical surface

Alternative representations are obtained for the high-frequency surface field excited on a perfectly conducting concave circular cylinder by an axial magnetic line current located on the surface. Included are ray-optical, canonical integral, whispering gallery mode, and near-field formulations, and various combinations of these. Asymptotic evaluations in different parameter ranges lead to results with varying accuracy and physical content. Their utility is assessed by extensive numerical calculations and comparisons. Most intriguing is a form of the asymptotic solution that involves only a number of geometric optical rays and a number of whispering gallery modes.     

Wire antennas over a lossy half-space

A recently developed technique for approximate but accurate evaluation of the various vector potential components associated with a current element radiating over a lossy ground is used to study the problem of antennas radiating over a lossy ground. A general integral equation for an arbitrarily shaped thin-wire antenna over a lossy half-space is derived, and the method of moments is employed to process this equation numerically. Illustrative numerical results are presented to demonstrate the effect of the lossy half-space on a number of antenna configurations.     

EM analysis of a conducting scatterer in optic dielectric waveguide

A method to compute the scattered field of curved mirrors and gratings in a dielectric slab waveguide is proposed. In contrast to the beam propagation method (BPM) for this kind of problems, the method of moment is adopted. By introducing the dyadic Green's function in a slab waveguide, the electric field integral equations for induced current distribution on the conducting obstacles are derived. To improve the computational efficiency, the modified Green's function is incorporated into the computation program. With this study, the effects of grooves of gratings and the finite extent of the mirrors in dielectric waveguides can be investigated in more detail     

Analytical form of EM fields radiated by circular aperture antennas of various current distributions

~~Analytical form of EM fields radiated by circular aperture antennas of various current distributions[1] Schelkunoff S. A., Advanced Antenna Theory, John Wiley &Sons, 1952. [2] E|liott R.S., Antenna Theory and Design, Prentice-Hall, Engie-wood Cliffs, N J, 1981. [3] R.W.P. King and G.S. Smith, Antennas in Matter: fundamen-tals, Theory and Applications, MIT Press, Cambirdge, MA,1981. [4] W.L. Stutzman and G.A. Thiele, Antenna Theory and Desigrn,John Wiley & S…     

Force on current coils moving over a conducting sheet with application to magnetic levitation

The use of Fourier-transform techniques provides exact integral expressions for the forces on polygonal dc current coils moving over a conducting sheet. These expressions are applied to investigate magnetic levitation of proposed high-speed transportation. Extensive numerical data have been analyzed to determine the performance dependence of the system parameters such as velocity, coil shape, array configuration, clearance, and track thickness, conductivity and permeability. In terms of potential applications, a comparison between the superconducting repulsive and ferromagnetic attractive systems is given.     

The physical optics fields of an aperture on a perfectly conducting screen in terms of line integrals

The physical optics fields due to an aperture on a perfectly conducting screen are expressed in terms of line integrals over the boundary of the aperture. These line-integral representations have the same properties as the ones in terms of surface integrals over the aperture; in particular, they admit arbitrary, source distributions, and are continuous everywhere in the source-free half-space, including the geometric optics shadow boundary.