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.     

Calculation and experimental validation of induced currents on coupled wires in an arbitrary shaped cavity

An efficient numerical technique is presented for the calculation of induced electric currents on coupled wires and multiconductor bundles placed in an arbitrary shaped cavity and excited by an external incident plane wave. The method is based upon the finite-difference time-domain (FD-TD) formulation. The concept of equivalent radius is used to replace wire bundles with single wires in the FD-TD model. Then, the radius of the equivalent wire is accounted by a modified FD-TD time-stepping expression (based on a Faraday's law contour-path formulation) for the looping magnetic fields adjacent to the wire. FD-TD computed fields at a virtual surface fully enclosing the equivalent wire are then obtained, permitting calculation of the currents on the wires of the original bundle using a standard electric field integral equation (EFIE). Substantial analytical and experimental validations are reported for both time-harmonic and broad-band excitations of wires in free space and in a high-Qmetal cavity.     

Shielding properties of an ensemble of thin, infinitely long,parallel wires over a lossy half space

A determination of the total electric field produced by an ensemble of thin, infinitely long, parallel wire scatterers over a flat lossy half space illuminated by a plane wave whose polarization is parallel to both the wires and the interface is presented. By invoking the thin wire idealization, a matrix equation is obtained for determining the currents on each wire, from which the total electric field is obtained. Several plots are given to show how the wires' radii, the earth's conductivity, the incident angle, and the total number of wires affect the shielding for a semicircular shell. In many cases, it is demonstrated that the shielding effectiveness can be as much as 70 dB; for other cases, when the structure is of resonant dimensions, the shielding can be degraded to 20 dB. It is also shown that a wire grid model can give shielding results similar to those of a continuous perfectly conducting structure of similar dimensions     

Analysis of the currents induced in a general wire cross by a plane wave incident at an angle with arbitrary polarization

Earlier analyses of the wire cross under restricted conditions are generalized, and a complete first-order solution is provided for the currents and charges per unit length in all four arms. These may have different and unrestricted lengths. The angles of incidence and polarization of the exciting plane wave are arbitrary. Detailed graphs are provided for the currents in and scattered fields of an equi-arm cross with electrical arm lengthskhup to 3.5 when the angle of incidence is45degand the electric vector is perpendicular to the horizontal wire. The included three resonances and the condition for a three-arm type of oscillation are treated. The critical effects of changes in the length of one of the vertical arms are examined for normal and nonnormal incidence.     

Bounds on the Load Currents of Exposed One-and Two-Conductor Transmission Lines Electromagnetically Coupled to a Rocket

Three circuits are analyzed. One consists of an isolated two-wire transmission line with terminating impedances; another of a single conductor with terminating impedances grounded to an infinite perfectly conducting plane; and, finally, a terminated two-wire transmission line in the vicinity of an infinite perfectly conducting plane. In all cases a plane monochromatic electromagnetic wave is incident on the wires with the electric vector parallel to their axes. The wires are oriented with respect to the incident field and the ground plane, if present, for maximum response. The objective is to derive formulas for the currents in the load impedances of the three circuit configurations described in the preceding. The writer then presents a heuristic argument to the effect that solutions of these problems bracket the response of exposed unshielded one-and two-wire transmission lines arranged parallel to the axis of a rocket and close to its surface. The established upper and lower bounds for the load currents are sufficiently close together to be of considerable practical value in the study of the electromagnetic compatibility of rockets.     

Scattering by wires near a material half-space

The currents in and the field scattered by a thin wire over a material half-space composed of earth, sea water or lake water are determined. Full account is taken of the effect of the half-space on both the currents indneed in the wire and on the scattered field. Distributions of current, back-scattering cross sections, and scattering patterns are shown for both normal and nonnormal incidence and with the incident field polarized in and perpendicular to the plane of incidence.     

平行金属线阵列地面附近的早期HEMP环境

铺设金属网的地面作为一种复杂的地表,区别于均匀半空间均匀地面,金属网必然会影响地表附近上方的电磁环境,因此,对其电磁环境的准确描述和分析十分必要。为此,以地面铺设平行金属阵列为典型情形,提出了一种计算平行金属阵列地面附近上方高空核爆电磁脉冲环境的解析方案,并且分析了地面铺设平行金属阵列结构之后对早期高空核爆电磁脉冲环境的影响。结果表明：当地面铺设平行金属线阵列后,相比于均匀半空间地面而言,不同高度下的水平极化场,反射场与入射场相互抵消的现象更加明显,使得总水平极化场衰减更为严重;而对于不同高度下的垂直极化场,其反射场和入射场的叠加现象也更加明显,使得地面附近上方的垂直场强幅值大于入射波场强幅值的效应加强。     

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     

Characteristics of a crossed-wire scatterer without a junction point of an incident wave of circular polarization

A crossed-wire scatterer has the wires displaced in the backscattering direction, and is able to scatter an incident wave of circular polarization in such a way that the backscattering wave has the same rotational sense as that of the incident wave. The radiation performance of the scatterer is improved by bending the horizontal and the vertical wires. Arrays consisting of crossed-wire scatterers are constructed and the backscattering cross sections (BSCS's) are calculated. It is revealed that the increase in the current amplitude due to the mutual effects among the array elements contributes to enhancement in the BSCS. It is also shown that a maximum value of the BSCS of an array of3 times 3bent crossed-wire scatterers is 1.8 times as large as that of a dihedral corner reflector which has the same aperture area. The BSCS's as a function of the angle of incidence are presented with experimental results at a frequency of 9.375 GHz.     

Transmission Line Mode Response of a Multiconductor Cable in a Transient Electromagnetic Field

This paper describes a technique for obtaining the induced worst case currents on individual wires of a multiconductor cable as a result of a transient electromagnetic radiation field. The technique involved a development of the expression for the induced current in matrix form where the mutual coupling terms and the other cable currents are the pertinent parameters. A worst case solution results from the assumption of maximum coupling orientation of the individual wires. A short example and some test results are presented. The test results show wave shapes for inductive and capacitive coupling. The solution for the individual wire current due to a transient electromagnetic field is important, since it will greatly reduce the required number of cable measurements and will allow the development of improved shielding techniques.     

Backscattering from a circular loop of wire

The geometrical theory of diffraction by a curved wire is used to calculate the backscattered field from a circular loop of wire at oblique incidence. The scalar cases of hard and soft wires and the electro-magnetic cases of horizontal and vertical polarization are treated. Graphs of the back-scattered amplitude versus angle of incidence are given for ka = 1, 2, . . ., 9 where k is the propagation constant and a is the loop radius.     

Analysis of the coupling of an incident wave with a wire inside a cavity using an FEM in frequency and time domains

This paper presents a numerical method based on finite elements in both the frequency and time domains for modeling the coupling of an incident wave with a conducting wire placed inside a metallic cavity having a small aperture. The method uses edge elements on tetrahedra for the electric field representation. The formulation can take into account thin wires as well as lumped elements. In the time-domain approach, the time derivatives are discretized by the Newmark method, which allows obtaining an unconditionally-stable scheme with second-order accuracy. Numerical results are provided to validate the presented method.     

Bounding EMP interaction and coupling

A technique is presented for obtaining upper bounds of the voltages and currents at terminations on a wire which is excited by an incident electromagnetic wave coupled through an aperture. The internal interaction and coupling problems are considered. Upper bounds are developed for the power waves launched on the wire structure and the termination signal levels are bound with a term included for multiple reflections. Tighter bounds are obtained by separating the incident field into individual parts typically characterized by poles in the complex frequency domain.     

Electromagnetic surface waves: New formulas and applications

Relatively simple and accurate formulas are now available for the complete electromagnetic field generated by vertical and horizontal dipoles located on or near the boundary between two electrically different half-spaces such as air and water or rock and sea water. The principal part of the field is an outward-traveling lateral wave with useful properties. The formulas are given and their application to a variety of problems reviewed briefly. These include: radio communication over the surface of the earth or sea, the wave antenna, communication with submarines using vertical dipoles in air and horizontal dipoles in the sea, the location of buried objects using horizontal dipoles on the surface of the earth, and the measurement of the conductivity of the sea floor.     

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     

On the Current Induced within an Infinitely Long Circular Cylinder (or Wire) by an Electromagnetic Wave

The current induced by a harmonic electromagnetic plane wave in an infinitely long wire is discussed. Two methods of calculating this current for a wire situated in vacuum will be compared: 1) one by Mohr [1] and 2) a direct calculation, which is given in Section II of this paper. Mohr's method 1) utilizes transmission line theory and the case of perpendicular incidence discussed in Jordan's book [2]. In the direct method 2) only Maxwell's equations and boundary conditions are used. When the direct method is presented in Section II, the wire is assumed to be situated in an arbitrary infinite homogeneous medium, not necessarily in a vacuum. In fact the direct method allows also the thickness and the material of the wire to be arbitrary, and so any infinitely long circular cylinder can be considered. It seems that the currents determined by Mohr's method and the direct method have roughly the same order of magnitude (at least), if the electromagnetic wave has a high-altitude-EMP frequency and is incident on a copper wire whose radius is less than about 1 cm and the angle between the line and the direction of propagation of the wave is above 45 ° . The agreement between Mohr's method and the direct method is better, the more perpendicular the incidence, the lower the frequency, or the smaller the radius of the wire.     

Low-frequency diffraction by a planar junction of a metallic and awire-mesh halfplane

The canonical problem of an electromagnetic field incident on a metallic halfplane joined to a wire-mesh halfplane is considered. It is assumed that the wire radius is small in comparison with the spacing between the wires, and that this spacing is small with respect to the free-space wavelength. Under this hypothesis, it is shown that the problem can be solved in closed form by using a Wiener-Hopf technique for any nonuniform electromagnetic incident field. The field transmitted through the structure is computed, considering as uniform sources both TE and TM incident planewaves     

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     

Analytical aspects of plane wave illuminated thin wires and slits

The paper deals with simple elementary approximations for the current and charge response on different straight wire structures, dipoles and short slits in the receiving case. After proof that transmission line equations are also valid for single wires without discontinuities, these equations are formulated including the incoming wave. They turn out have simple particular solutions that could be expected for the case, when the electric field is parallel to the wire, but holds true for the general case too. Satisfying the boundary condition at discontinuities (wire ends, lumped elements) gives rise to additional waves appearing as solutions of the homogeneous wave equation. The formulation of currents along and voltages across a slit, including an illuminating magnetic field at one side of the screen, leads again to transmission-line type equations and, consequently, to the inhomogeneous wave equation. As slits in screens are usually small in terms of wavelength, an approximative solution for the short slit will do. For this case, even closed-form expressions are possible for the magnetic near field     

On the backscattering from two arbitrarily located identical parallel wires

A study of the backscattering from two identical perfectly conducting, thin wires illuminated by a plane wave at an arbitrary angle of incidence is presented. The theory is based on an integral equation method. By decomposing the induced currents into symmetric and antisymmetric modes, the simultaneous integral equations for the induced currents are converted into independent integral equations similar to the one for a single wire for which the solution has already been carried out. The induced currents on and the backscattering cross sections of the wires are determined. Numerical examples include nonstaggered, staggered, and collinear cases of both half-wave and full-wave wires. Comparisons are made between the calculated and measured values of the echo area. The experimental results are in good agreement with theory.