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.     

Waveguide antennas illuminating a metal sheet

Experimental measurements of the admittance of rectangular or circular waveguide-fed apertures illuminating a displaced conducting plate of finite area are compared with calculations where the antenna ground plane and displaced conducting boundary are infinite in extent. Also, included are results where dielectric plugs are placed in the aperture.     

High-frequency transmission line models for a thin wire above aconducting ground

Full-wave transmission line models are constructed for a thin wire above a conducting ground. The transmission line models are based on a reciprocity theorem rather than on power assumptions. Different models are considered where the current or the voltage in the transmission line model has physical significance. The models describe the propagation of the fundamental mode in the waveguide structure consisting of the wire and the conducting ground. The characteristics of this mode, needed for the models, are determined with a spectral domain technique     

Bounds on the electric field outside a radiating system--II

Bounds on the near electric field outside a rectangular aperture in a conducting ground plane are obtained and analyzed. The results are used to predict the power limitations (due to microwave breakdown) for such apertuares.     

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.     

Influence of a lossy ground on lightning-induced voltages onoverhead lines

A comprehensive study on the effect of a lossy ground on the induced voltages on overhead power lines by a nearby lightning strike is presented. The ground conductivity plays a role in both the evaluation of the lightning radiated fields and of the line parameters. To be calculated by means of a rigorous theory, both fields and line constants need important computation time, which, for the problem of interest, is still prohibitive. The aim of this paper is to discuss and analyze the various simplified approaches and techniques that have been proposed for the calculation of the fields and the line constants when the ground cannot be assumed as a perfectly conducting plane. Regarding the radiated electromagnetic field, it is shown that the horizontal electric field, the component which is most affected by the ground finite conductivity, can be calculated in an accurate way using the Cooray-Rubinstein simplified formula. The presence of an imperfectly conducting ground is included in the coupling equations by means of two additional terms: the longitudinal ground impedance and the transverse ground admittance, which are both frequency-dependent. The latter can generally be neglected for typical overhead lines, due to its small contribution to the overall transverse admittance of the line. Regarding the ground impedance, a comparison between several simplified expressions used in the literature is presented and the validity limits of these expressions are established. It is also shown that for typical overhead lines the wire impedance can be neglected as regard to the ground impedance     

Image radiation from a finite ground plane in two dimensions

A simple expression for the image radiation of an array of line sources parallel to a conducting strip is derived, in terms of the known image radiation from the same sources above an infinite ground plane. Simple criteria are presented for the minimum strip width which will produce essentially the same image radiation as an infinite ground plane, for angles above the strip plane greater than some prescribed value.     

The radiation pattern of an array of dipoles in a dielectric slab

By using the reciprocity theorem, simple expressions are derived for the far-field patterns of normal and parallel dipoles in a plane dielectric slab. The dielectric slab may have a conducting ground plane on one surface. Numerical results are presented in a graphical form to show the effects of the dielectric on the antenna pattern. A dipole array embedded in a radome occupies less space than a conventional parabolic antenna, and the ground plane offers structural support for the radome.     

Radiation properties of a pigtail-terminated coaxial transmissionline

The method of moments is used to study the shielding effectiveness of a pigtail-terminated shielded wire (coaxial line) above a perfectly conducting ground plane. Numerical computations are performed in the RF frequency range, i.e. 25-1000 MHz. Pigtail wires on either or both ends of the shield are considered. Results are compared to those from the ungrounded case (floating shield). Results show that the presence of pigtail wires as ground connections at RF frequencies is undesirable and may further enhance radiation. The impedance terminations have a small effect on the shielding effectiveness of the antenna structure     

Gaussian beam scattering from a conducting cylinder partially buried in a ground plane

The problem of scattering from an infinitely long conducting cylinder that is partially buried in a perfectly conducting ground plane due to an obliquely incident gaussian beam is solved by an exact procedure based on the method of images by first adopting a simplification originally proposed by Kozaki. The incident and the specularly reflected fields are expressed in terms of cylindrical vector wave functions multiplied by a weighting function which involves the beam parameters like the radial distance of the source and beam width. The scattered fields originating from the cylinder and its image in the ground plane are expressed in terms of cylindrical vector wave functions. The boundary conditions on the surface of the cylinder are then imposed and this procedure leads to a coupled infinite system of equations for the even and odd mode expansion coefficients of the scattered field. These equations are solved numerically for the case of cylinders having electrical radius in the Rayleigh and resonance regions. Both the transverse magnetic and transverse electric polarizations of the incident beam wave are considered and some representative numerical results for the scattered far-field are presented in graphical form. The magnitude of the induced current for the TM polarization is calculated and compared with the corresponding case of plane wave incidence.     

Effect of dielectric jacket on a buried travelling-wave antenna

Transmission line theory has long been used to analyze the performance of dielectric-coated buried antennas. However, at UHF the ground cannot be assumed to be highly conducting and a new approach is necessary. A method is presented to predict the input impedance and pattern of a dielectric-coated traveling-wave antenna buried in lossless ground.     

Electromagnetic wave propagation on a double-layer dielectric film

The nature of the eigenvalues characterising the electromagnetic wave propagation in a homogeneous isotropic double-layer dielectric structure of infinite extent on a perfectly conducting ground plane is discussed.     

Eigenmode analysis of dielectric loaded top-hat monopole antennas

Eigenmode expansions are used for computing the currents on a dielectric loaded top-hat monopole radiating above an infinite conducting ground plane. The approach is facilitated by adding a parallel ground plane above the antenna, thus allowing use of cylindrical harmonic field expansions in each of three regions. Expansion coefficients are found by enforcing boundary and continuity conditions at conducting surfaces and regional interfaces. Convergence and accuracy are assessed using comparisons with three other methodologies, namely an integral equation solution, a quasi-static analysis, and multi-octave experimental measurements     

Radiation and scattering from electrically small conducting bodies of arbitrary shape above an infinite ground plane

A simple moment solution is given for the low-frequency electromagnetic scattering or radiation problem involving a small perfectly conducting body of arbitrary shape placed close to an infinite ground plane. The method of images is used to account for the presence of the ground plane. The dynamic problem is approximated by two uncoupled problems, an electrostatic one and a magnetostatic one. Each static problem is then solved using the method of moments. The surface of the perfectly conducting scatterer is modeled by a set of planar triangular patches. Pulse expansion and point-matching testing are used in the electrostatic problem. For the magnetostatic problem, a set of solenoidal vector expansion functions is used. The induced dipole moments are computed from the induced electrostatic charge and the magnetostatic current densities. The scattered field is the field of these induced dipoles oscillating with the frequency of the incident field. Scatterers of various shapes are studied. Special attention is given to a conducting box on the ground plane.     

Calculation methods of electromagnetic fields very close to lightning

In this short paper, we present two methods: Quasi-images formula and finite-difference time-domain (FDTD) method to evaluate the electromagnetic fields very close to lightning channel, which are applicable for poorly conducting ground case, and the numerical results are consistent with each other. Moreover, the vertical electric fields at 15 m obtained by the two proposed methods is in good agreement with the measured result, and the horizontal electric field at a distance of 100 m above finely conducting ground obtained by the FDTD method is identical to the field obtained by accurate Cooray-Rubinstein approximation. With the proposed quasi-images formula, the effects of electrical dispersion of the ground on the lightning generated electromagnetic fields are analyzed and some significant results are obtained.     

Calculation of radiation patterns of a Yagi antenna above imperfectly conducting ground

A computer program is presented for the calculation of radiation patterns of Yagi antennas, having up to ten elements, located above a plane imperfectly conducting ground.     

The radiation efficiency of a dipole antenna located above an imperfectly conducting ground

The dyadic Green's function technique is used to develop integral expressions for the radiation efficiency of three types of dipole antennas located above an imperfectly conducting, infinite ground plane. The three antennas treated are: 1) vertical Hertzian dipole, 2) horizontal Hertzian dipole, and 3) a vertical half-wave dipole with sinusoidal current distribution. The results of numerical evaluation of the integral expressions for several values of ground constants are presented in graphical form. The radiation efficiency of a vertical Hertzian dipole is found to exhibit a distinct peak when located at a height of one-eighth wavelength.     

Radiation from a dielectric coated hemispherical conductor fed by acoaxial transmission line

A dielectric-coated hemispherical conductor mounted on an infinite perfectly conducting ground plane and fed by a coaxial transmission line is investigated. Green's functions for the region above the ground line are derived with separated homogeneous and particular solution parts so as to be compatible with numerical analysis techniques. A magnetic field integral equation is constructed in terms of the unknown annular aperture tangential electric field and is solved by the method of moments. A comparison of the characteristics of the dielectric-coated hemispherical conductor and a flush-mounted coaxial line to an infinite homogeneous region above the ground plane is presented with respected to the tangential aperture electric field, with respect to the tangential aperture electric field, the coaxial line apparent input impedance, and the far radiated field     

Low-frequency impedance of a circular loop over a conducting ground

Using a quasistatic approach, the input impedance of a circular wire loop is calculated for the case where the Earth is represented as a homogeneous conducting halfspace. It is shown that the input resistance is only proportional to the ground conductivity when the loop radius is small compared with the electrical skin depth.     

Radiation characteristics of an infinite dielectric-coated axiallyslotted cylindrical antenna partly embedded in a ground plane

The radiation characteristics of an axial slot on a dielectric-coated conducting circular cylinder embedded in a semi-circle in an infinite ground plane (GP) are examined. The boundary-value method is employed to obtain the solution with the aid of the partial orthogonality of the trigonometric functions. The resulting dual infinite series involved in the solution is then truncated to generate numerical results. The geometry considered here is important because it can be implemented on the body of any mobile communication system. Moreover the GP adds a new parameter to the slotted dielectric-coated conducting circular cylindrical antenna and can be used in beam shaping and to enhance the antenna performance