The Response of a Terminated Two-Wire Line Suspended in Air Above a Semi-Infinite Dissipative Medium and Excited by a Plane-Wave RF Field Generated in Free Space

The analysis previously made to determine the response of a two-wire transmission line buried at constant depth near the earth-air interface when excited by a plane-wave electromagnetic field generated in free space is extended to include the case of the line suspended in air at a uniform distance above the earth's surface. The exciting field is the vector sum of the incident and reflected fields at the point midway between the line conductors. The polarization of the electric field is taken to be parallel to the wires, so that there is no pick up by the terminations. The objective of the study is to determine bounds for the current in specified load impedances in terms of the amplitude of the incident electric field evaluated at the surface of the earth.     

Transmission Line Coupled to a Cylinder in an Incident Field

An approximate formula is derived for the currents in the loads terminating a two-wire line located parallel to and near a circular conducting cylinder of finite length. The line and the cylinder are illuminated by an incident plane wave. The analysis takes account of the coupling between the line and the cylinder and hence of the effects of possible axial resonances in the latter. The configuration simulates exposed conductors used to interconnect the electronic apparatus in a rocket. The analysis is directed toward determining possible hazards due to induced currents.     

Generalized Theory of Impedance Loaded Multiconductor Transmission Lines in an Incident Field

A general theory is advanced for determining the currents in the load impedances of an N-conductor isolated transmission line excited by an electromagnetic field with the electric vector directed parallel to the wires. The number of impedance loads in the circuit is 2N. An impedance is connected in series with each conductor at its ends. At each end of the transmission line the impedances emanate from a common node. There is no requirement that the conductors be of the same radius, be equally spaced, or lie in a common plane; however, their axes must be parallel. Evidently the cross section of the line must be sufficiently small in terms of the wavelength that transmission line theory applies. Numerical values for the load currents In a three-conductor model are given. Scattering from end loaded multiconductor transmission lines is considered. It is shown that for configurations lacking geometrical symmetry such problems become arduous if not solved by computer.     

The Response of a Terminated Two-Wire Line Buried in the Earth and Excited by a Plane-Wave RE Field Generated in Free Space

A terminated two-wire transmission line is buried at constant depth near the earth-air interface with one conductor directly below the other. A plane-wave electromagnetic field, generated in free space, impinges upon the boundary where it undergoes partial reflection and transmission. The field transmitted into the earth excites the transmission line. The polarization of the electric field is chosen such that the field is directed parallel to the line conductors. The interaction of the line with the dispersive medium and the line losses are considered. The objective of the study is to determine the current in specified load impedances in terms of the amplitude of the incident electric field evaluated at the surface of the earth.     

Analysis of a four parallel wire antenna system by the spatialFourier transform method

The electromagnetic fields and currents associated with an infinite four parallel wire transmission line are analyzed through the use of the spatial Fourier transform method. The near and far electromagnetic fields and currents that are associated with frill and gap voltage excitations are analyzed by the Fourier transform method. Possible VHF compact range applications of a four parallel wire antenna system are discussed, including the possibility of simulating an off-axis EM plane wave by the appropriate adjustment of the exciting voltage phase on each of the four parallel wires. Comparisons of Fourier transform method solutions with method-of-moments solutions and finite-difference-time-domain solutions are made for an infinite four parallel wire antenna system     

Excitation of an External Terminated Longitudinal Conductor on a Rocket by a Transverse Electromagnetic Field

A single conductor of arbitrary length is placed close to the surface of a conducting cylinder parallel to its axis. Impedances are connected between the ends of the cable and the cylinder. An incident monochromatic plane electromagnetic wave propagates in the longitudinal direction and is thus polarized in a transverse plane with respect to the axes of the external conductor and the cylinder. The component of the electric field tangent to the terminating impedance excites the circuit. The objective is to derive formulas for the currents in these impedances. The transverse dimensions of the conductor satisfy the inequalities a1 ? a2 ? ?, where a1 is the radius of the external conductor and a2 is the radius of the cylinder. It is assumed that the distance d between adjacent points on the conductor and the rocket is small compared with the wavelength.     

The shielding of a plane wave by a cylindrical array of infinitely long thin wires

A plane wave is considered to be incident upon a cylindrical array of infinitely long perfectly conducting thin wires. The wave is assumed to have no magnetic field component in the direction of the wire axes. Exact expressions are found for the currents excited on the wires-and for the total electric and magnetic fields. Numerical computations are made to determine the currents on the wires and the fields inside the array. It is discovered that an important parameter is the number of wires in the array divided by the number of wavelengths that can be wrapped around the cylinder. If this parameter is large enough, the current distribution on the wires resembles that of a solid conducting cylinder, and the array of wires tends to behave like an electromagnetic shield. For smaller values of the parameter, the current distribution can be quite different, and the field inside the array may even be enhanced.     

On the Excitation of a Coaxial Line by an Incident Field Propagating Through a Small Aperture in the Sheath

A coaxial line having a small aperture in the sheath and terminating in arbitrary impedances is considered to be illuminated by an incident plane wave. The excitation of currents in the termination impedances is shown to depend upon three independent factors. Simple analytical forms are given for equivalent voltage and current sources of the aperture excitation.     

Electromagnetic field coupling to a line of finite length: theoryand fast iterative solutions in frequency and time domains

A system of integral-differential equations for evaluating currents and voltages induced by external electromagnetic fields on a finite-length horizontal wire above a perfectly conducting ground is derived under the thin wire approximation. Based on perturbation theory, an iterative procedure is proposed to solve the derived coupling equations, where the zeroth iteration term is determined by using the transmission line (TL) approximation. The method can be applied both in the frequency and in the time domains. The proposed iterative procedure converges rapidly to the exact analytical solution for the case of an infinite line, and to the NEC solution for a line of finite length. Moreover, with only one iteration, an excellent approximation to the exact solution can be obtained. The method is applied to assess the validity of the TL approximation for plane wave coupling to an overhead line of finite length. It is shown that the resulting errors for the early-time response are generally higher than those corresponding to infinite lines     

Rayonnement d’une grille plane de fils continus et discontinus

This paper relates the scattering of a electromagnetic plane wave by a plane grating of conducting wires. The wires are parallel, equidistant and alternatively continuous and discontinuous. The discontinuous wires may be considered as dipole lines. The problem is numerically resolved. The conductor currents are determined by means of a system of first kind integral equations which is converted in a linear equations system by the moments method. The knowledge of currents permits the calculation of the reflection and transmission factors of the grating. Thus a matched state and a resonant state appear for discrete frequencies, where the transmission factor modulus is respectively 1 and 0. Experimentation on waveguide simulators gives a good agreement with numerical results.     

Finite length cylindrical scatterer near perfectly conducting ground--A transmission line mode approximation

A Pocklington type integro-differential equation, possessing an exact kernel, is formulated in terms of a complex frequency for the current induced on a thin finite-length cylindrical scatterer which is above, near, and parallel to a perfectly conducting ground plane. The circumferential variation of the axial current is assumed to be described by a transmission line mode approximation when the scatterer is near the ground plane. The integro-differential equation is reduced to a system of algebraic matrix equations through application of the method of moments. The singularity expansion method is utilized to determine the transient current response of the cylindrical scatterer to a unit step incident plane wave. Complex natural frequencies, natural mode vectors, normalization coefficients, and induced currents are compared to those found through a similar procedure with an approximate kernel, which assumes uniform circumferential variation of the axial current. The exact kernel with an assumed circumferential variation of the axial current is shown to be necessary when the thin cylindrical scatterer is near the ground plane.     

Electromagnetic coupling to a conducting wire behind an aperture of arbitrary size and shape

The electromagnetic coupling to a conducting wire behind an aperture in a plane conducting screen is analyzed. The aperture can be of arbitrary size and shape. The wire can be of finite length, with or without terminating loads, or of infinite length. The electric current on the wire and the equivalent magnetic current over the aperture region are calculated by the method of moments. An equivalent circuit for the effect of the aperture on the transmission line mode of the wire is derived.     

Full-wave analysis of coupled perfectly conducting wires in amultilayered medium

A full-wave analysis of coupled perfectly conducting cylindrical wires in a multilayered dielectric medium is presented. The analysis is based on a Fourier series expansion of the unknown surface currents on each wire and on an integral equation for the longitudinal field on the wires. The calculations are not restricted to the propagation constants of the different modes, but explicit results are presented for the impedances associated with each wire and each eigenmode as a function of frequency. Propagation constants, longitudinal currents on the wires, and impedances lead to a complete equivalent circuit for the structures being considered     

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.     

Analytic formulation of the response of a two-wire transmissionline excited by a plane wave

A perfectly conducting uniform two-wire transmission line of finite length illuminated by a plane wave is considered. The induced voltage and current-responses are described by analytic expressions in the frequency and time domains. Moreover, an instructive case study is presented. This simplified and cost effective method can be an important part of the theoretical NEMP-analysis of systems     

Calculation of the characteristics of two-wire lines in multiconductor cables

A rigorous method is proposed for calculating the parameters of two-wire lines (twisted pairs) surrounded by a single metal shield and the mutual coupling between these lines. It is shown that coupling between the lines in multiconductor cables results in electromagnetic interference (crosstalk) in communications channels and that inphase currents in the lines are caused by the asymmetry of excitation and loads. The stray voltages induced across the impedances placed at the beginning and the end of an adjacent line are determined at a given power in the main line. The effect produced by the loads placed between the wires and the shield is considered. The proposed method allows generalization of the obtained results to the case of lossy multiconductor cables.     

Plane-wave Reflection and Transmission by Grids of Conducting Ω-particles and Dispersion of Ω Electromagnetic Crystals

Plane-wave reflection and transmission by 2D grids formed by Ω-shaped conducting particles connected by their arms and dispersion properties of an infinite set of such grids are studied. Arms of connected Ω-particles are collinear, and every grid can be considered as a mesh of parallel wires periodically loaded by loops. These loops are parallel to one another and lie in planes orthogonal to the grid plane. The grids are bianisotropic and self-resonant. An analytical model of such a grid is proposed and then used so that to study the dispersion properties of 3D lattices. The dispersion and polarization properties of the 3D Ω-lattice (a bianisotropic electromagnetic crystal) are close to those of a lattice from inductively loaded wires. Such structures can be prospective for frequency filtering and antenna reflectors and substrates.     

On the wide-band CW illumination of large-scale systems. II. Therhombic illuminator

The Phillips Laboratory has designed and constructed a continuous wave illuminator for studying the responses of large-scale systems subject to vertically or horizontally polarized electromagnetic stresses incident from the horizontal. The illuminator is developed by a nonuniform two-wire transmission line oriented over the system under test. When the wires are driven from a common mode voltage with respect to the ground a vertically polarized electric field is generated and when the wires are driven from equal but opposite voltages a horizontally polarized electric field is developed. The structure is called the rhombic illuminator since the wire configuration is very similar to the rhombic antenna. In order to illustrate the use of the illuminator, data are presented for the illumination field and for the response of an illuminated aircraft recorded at the Phillips Laboratory     

Image theory for DC problems involving a conducting half-spacebounded by a perfect anisotropic impedance surface

Image theory is developed for the canonical direct current problem involving a point current source in a conducting half-space bounded by a planar perfect anisotropic surface (PAS). The anisotropy of the surface is perfect in the sense that it has infinite conductivity in one direction and zero conductivity in the perpendicular direction. A PAS plane can be realized by a layer of perfectly conducting parallel wires isolated from one another. It is seen that the image of a current point source is a quadrupole transverse-magnetic current extending along a half-infinite line     

Three-dimensional diffraction by infinite conducting and dielectric wedges using a generalized total-field/scattered-field FDTD formulation

We extend the generalized total-field/scattered-field formulation of the finite-difference time-domain method to permit efficient computational modeling of three-dimensional (3-D) diffraction by infinite conducting and dielectric wedges. This new method allows: 1) sourcing a numerical plane wave having an arbitrary incident angle traveling into, or originating from, a perfectly matched layer absorbing boundary and 2) terminating the infinite wedge inside the perfectly matched layer with negligible reflection. We validate the new method by comparing its results with the analytical diffraction coefficients for an infinite 3-D right-angle perfect electric conductor wedge obtained using the uniform theory of diffraction. Then, we apply the new method to calculate numerical diffraction coefficients for a 3-D infinite right-angle dielectric wedge, covering a wide range of incident and scattering angles. Finally, we show means to compactly store the calculated diffraction coefficients in a manner which permits easy interpolation of the results for arbitrary incidence and observation angles.