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.     

Eigenvalues of a dielectric-coated conducting cone

The general problem of radiation/scattering from a dielectric coated semi-infinite conical structure excited by an arbitrary surface current distribution on the dielectric layer is formulated. Since the angular eigenfunction expansion is not suitable for this problem, the radial eigenfunction expansion is employed. The boundary value method is applied to obtain the fields in the form of infinite double series over the appropriate eigenfunctions in terms of spherical Hankel and associated Legendre functions. The conical dielectric shell may be lossy or lossless and the series solution generally involves complex eigenvalues which are calculated numerically. Using a small conducting sphere at the tip of the cone, the singularity of the Hankel functions at the origin is overcome, thus permitting the use of the orthogonality relations of Sommerfeld's complex-order wave functions to solve the problem and construct sets of infinite simultaneous linear equations which are presented in matrix form.     

Electromagnetic transient response of a spherical conducting shell over a conducting half-space†

The quasi-static response of a thin spherical conducting shell over a conducting half-space is derived for plane-wave illumination. The waveform of the transient scattered field consists of two decaying exponentials whoso time constants uniquely specify the shell radius and conductivity-thickness product. The coupling between the shell and the ground is also examined.     

EM fields of a phased line current over a conducting half-space

The need often arises to predict the electromagnetic field of power and communication lines over the earth. A simple and explicit derivation is given for the electromagnetic fields of a travelling current line source located over a layered conducting half-space. Special attention is paid to the case of a homogeneous half-space where analytical closed-form expressions can be obtained. Of some interest is the radiation of a vertically polarized radio ground wave which would not be present if the line source was uniform     

Radiation pattern of a vertical linear antenna over a conducting strip

The theoretical and experimental radiation patterns of an extended vertical line antenna placed over an infinite conducting strip are presented. The results show the nature of dependence of the level of back radiation upon the strip width and antenna height.     

Radiation characteristics of corrugation loaded dielectric-coated conducting cylinder

The radiation characteristics of a corrugation loaded dielectric coated conducting cylinder are investigated theoretically for the infinite periodic and finite structures. For the infinite periodic structure, the mode matching method is applied. The integral equation is derived for the finite structure by use of the Fourier transform and mode expansion. The influences of the corrugation width, corrugation depth, dielectric thickness, cylinder radius, and finite corrugation number on the radiation characteristics (leakage constant, phase constant, and radiation pattern) are investigated. The results of the finite periodic corrugations are compared with those of the infinite extent structure and good agreement is found. To reduce the high side lobe of the uniform periodic structure, nonuniform quasiperiodic corrugation arrays are considered. The surface wave radiated by the structure having end-fire radiation pattern is also investigated.     

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 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     

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     

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.     

The equivalent radius of a narrow conducting strip

By means of a simple and direct analytical procedure, it is confirmed that the equivalent radius of a narrow conducting strip is one-fourth its width. The analysis proceeds from the integral equation for the surface current density induced on a conducting cylinder of general cross section and its incorporates knowledge of the current density induced on a narrow strip. Explicit expressions are given for the total axial current induced on the narrow strip and for its echo width.     

Scattering by a conducting strip with a periodic edge

The electromagnetic field scattered by a conducting strip with a periodic edge consists of a finite number of radiating, generally depolarized, modes. The relative intensities are estimated by using the physical optics approximation for the induced current.     

Air-to-subsurface communication in an anisotropic conducting half-space

To study the propagation of electromagnetic waves in the sedimentary formations (to locate trapped miners) and also in the idealized jungle environment, a boundary value problem is formulated and the fields of a low-frequency (<100 kHZ) vertical electric dipole placed at the surface of a homogeneous anisotropic conducting half-space are evaluated. Some numerical computations have been performed and the curves are plotted to focus attention on the field modifications inside the medium due to the effect of anisotropy. Significant change in the attenuation rate is observed with the change in 1) the position of the observer, and 2) the value of the coefficient of anisotropy.     

Radiation patterns of an antenna near a conducting strip

Horizontal patterns of a linear antenna near a conducting strip are found by solving a two-dimensional problem using an integral equation method. Because of practical interest, the computed patterns are shown for only small to moderate sizes of the strips and small to moderate separation distances of the antenna.     

Electromagnetic scattering by a conducting strip with a multilayerelliptic dielectric coating

The scattering of an electromagnetic plane wave by a conducting strip coated with a multilayer elliptic dielectric is considered. The solution of this problem is carried out by using an expansion of the electromagnetic field in terms of Mathieus functions and by implementing an efficient procedure for the “treatment” of the boundary conditions. This procedure could be a useful tool for checking the accuracy of numerical techniques widely used in electromagnetic compatibility, as it allows the solution of one of the few canonically solvable scattering problems involving perfectly conducting objects with sharp edges and inhomogeneous dielectrics. Many numerical results concerning the scattering cross section per unit length are provided and, where possible, they are compared with already available results. We consider only perpendicular incidence, although oblique generalization is conceptually easy     

Resonances of perfectly conducting wires and bodies of revolutionburied in a lossy dispersive half-space

The method of moments (MoM) is utilized to compute the complex resonant frequencies and modal currents of perfectly conducting wires and bodies of revolution buried in a lossy dispersive half space. To make such an analysis tractable computationally, the half-space Green's function is computed via the method of complex images, with appropriate modifications made to account for the complex frequencies characteristic of resonant modes. Results are presented for wires and bodies of revolution buried in lossy soil using frequency-dependent measured parameters for the complex permittivity, and we demonstrate that the resonant frequencies generally vary with target depth. In addition to presenting results, relevant issues are addressed concerning the numerical computation of buried-target resonant frequencies     

One-dimensional profile inversion of a half-space over a two-partimpedance ground

A method which permits one to reveal the one-dimensional (1-D) electromagnetic profile of a half-space bounded by a two-part impedance ground is established. The method reduces the problem to the solution of two functional equations. One of these equations is solved exactly by reducing it to a Riemann-Hilbert problem while the other is reduced under the Born approximation to a Fredholm equation of the first kind whose kernel involves the solution to the first equation. Since this latter constitutes an ill-posed problem, its regularized solution, in the sense of Tikhonov, is given. An illustrative application shows the applicability and the accuracy of the theory. The functional equations are valid also when the impedance of the ground varies in an arbitrary manner. The theory can be applied to a quick determination of the constitutive electromagnetic parameters of the atmosphere over a nonhomogeneous impedance ground