Transient plane wave coupling to bare and insulated cables buriedin a lossy half-space

The current induced on an infinite bare or insulated cable buried in a lossy earth medium due to a transient plane wave is presented. An exact solution is formulated in the frequency domain using a spatial transform under the thin-wire approximation. The widely used equivalent circuit transmission line model is derived from the exact solution. Results are presented for typical transmission structures under high frequency transient excitation and the exact solution is compared with the transmission line approximation. The transmission line approach provides good results for a wide range of cases. For accurate results in the high frequency situation it is necessary that the correct incident field expressions be used and that a complete representation of the earth's electrical properties (σ and ϵ) be retained     

Comparison of Quasi-Static and Exact Electromagnetic Fields from a Horizontal Electric Dipole Above a Lossy Dielectric Backed by an Imperfect Ground Plane

In most microstrip transmission lines, analysis is made assuming that a quasi-TEM mode exists and propagates down the line. The primary objective of this paper is to obtain the region of validity of this assumption. The second objective of this paper is to derive the expressions for the fields for a horizontal electric dipole over a Iossy dielectric medium backed by an imperfect ground plane. It is shown that, to a first approximation, fields at the air-dielectric interface are independent of the ground plane conductivity. Since we are interested in coupfing between lines, our interest is in the computation of the fields primarily at the air-dielectric interface. Finally, numerical results are presented to show where the quasi-static approximations deviate from the exact solution for a given microstrip geometry as the frequency of operation or the observation point is changed.     

A new representation for the Green's function of multilayer media based on plane wave expansion

In this paper, a new representation for the space domain Green's function of general multilayer media is presented. This approach is based on an efficient plane wave expansion of the source incident field. Using the transmission line model for the multilayer medium, the effect of the layered medium on the incident plane waves is determined by a transmission coefficient, and the amplitude and phase of each plane wave at the field point are obtained. The total field is evaluated by summing the resultant plane waves at the field point. The main advantage of the proposed method is that the spatial domain Green's function of multilayer media can be obtained easily as a summation of simple exponential functions, without the need for Sommerfeld integration or complex image approximation. The plane wave approximation is independent of the parameters of the medium and is valid over a wide frequency range. Furthermore, the exponential form of the plane wave solution makes it possible to compute the method of moments matrix elements analytically for most important types of basis functions in multilayer problems.     

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 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     

Surface current and charge density induced on aircraft

The usefulness of the geometrical theory of diffraction (GTD) in computing the surface current and charge density induced on aircraft is illustrated. This is a high-frequency solution for an arbitrary incident plane wave and fuselage observation points. A pattern is presented for an arbitrary incident plane wave as well as a series of frequency and time domain plots for roll plane incidence. A 3-dimensional pattern is presented for plane wave incidence (as a function of incidence angle) as well as examples of roll plane results in both the frequency and time domain.     

External field coupling to MTL networks with nonlinear junctions:numerical modeling and experimental validation

The problem of predicting the voltages and currents induced on a printed circuit multiconductor transmission line (MTL) network by an impinging transient plane wave electromagnetic field is considered. The MTL network contains nonlinear circuit elements and test cases with various dielectric substrates are examined. Numerical predictions based on quasi-TEM models of the MTL and modified nodal analysis (MNA) models of the lumped element junctions are compared to experimental results obtained in the time domain using a GTEM cell. As has been done in the past, the effect of the incident plane wave is introduced as forcing functions in the MTL equations. The primary goal of this paper is to quantify the accuracy of the various commonly used quasi-TEM mathematical time-domain models. It is shown that when modeling the forcing function terms, it is important to take into account the perturbation of the incident plane wave due to the dielectric substrate. (The experimental-numerical comparisons herein are shown for the case of end-fire illumination since it best demonstrates this point.) Neglecting the dielectric effect on the incident transient pulse, even for substrates with low dielectric constant, produces poor results     

Propagation of the Quasi-TEM Mode in Ferrite-Filled Coaxial Line

The Suhl and Walker approximation for the propagation constant of the quasi-TEM mode in ferrite-filled parallel plane waveguide has been applied to the ferrite-filled coaxial line. The approximation is compared to exact solutions for a coaxial line filled with a lossless ferrite with close agreement. The propagation constant of the quasi-TEM mode is determined by measuring the complex reflection coefficient of a plane ferrite-air interface. The /spl alpha/ and (/spl beta/ are compared to the Suhl and Walker approximation with losses, and qualitative agreement is found. In order to relate the measured values to the propagation constants, the boundary value problem of the reflection from a plane ferrite-air interface is investigated. Expressions are derived which relate the real and imaginary parts of the propagation constant in the ferrite to an approximation to the complex reflection coefficient of the TEM mode in the empty line.     

On the coupling of an external electromagnetic field to a printedcircuit board trace

Compact analytical solutions are developed for the terminal responses of a printed circuit board (PCB) trace exposed to an external electromagnetic field in the frequency and time domain. The analysis based on transmission line theory in a scattered voltage formulation uses a quasi-TEM propagation model for the trace and the exact distribution of the external electric field within the air/dielectric medium for the excitation terms. From the general solutions obtained for arbitrary wave incidence and terminal impedances, several much simpler approximations are derived revealing the principal behavior and indicating the relevant parameters to minimize the coupling. Practical examples with a comparison of the different results are presented     

A simple technique for calculating the propagation dispersion ofmulticonductor transmission lines in multilayer dielectric media

A multiconductor transmission line in a multilayer dielectric medium is complicated and therefore is frequently analyzed by the simple quasi-TEM (transverse electromagnetic) approach. Unlike the full wave eigenvalue approach, the quasi-TEM approach does not give the propagation dispersion characteristics of the line. This work overcomes this problem by first obtaining the solution of each multiconductor mode from the quasi-TEM approach. Then these solutions are used as both basis and testing functions in a variational formulation of the full wave eigenvalue analysis. The result is high accuracy in the dispersive propagation constants of the multiconductor modes. By solving only for high frequency eigenvalues, not for the high frequency eigenvectors, the method is simpler and faster than the conventional full wave dispersion analyses     

Onde quasi-TEM des guides cylindriques blindés

tem approximation technique is widely used in the study of waveguides characterized by the fundamental mode without cutoff frequency. It seems that exact justification of this approximation has never been delt with before to his knowledge. Here the author is trying to show the justification for a closed waveguide noting the difference between a quasi-TEM wave and an ordinary tem wave.     

Dipole Mode Response of a Multiconductor Cable Above a Ground Plane in a Transient Electromagnetic Field

This paper describes an analytical technique that may be used to obtain the worst case dipole mode currents on individual wires of a multiconductor cable as a result of a transient electromagnetic radiation field. The dipole mode response is due to the E field parallel to the length of the cable. To obtain the solution, the conductors and their image in the ground plane are considered as forming a loop, and the resultant loop is solved as a transmission mode loop. The solution is given in matrix form as an upper bound of the true current including both mutual inductive and mutual capacitive coupling. The mathematical results are presented in the time domain and are uniquely applicable to experimental results obtained in EMP simulation with narrow pulse driving fields.     

Time Domain Shielding Properties of Conducting Cylindrical Shells

Transient shielding properties of a conducting cylindrical shell with; an EMP incident plane wave are obtained through numerical Fourier transforms of the frequeny domain solution. Anomilous resonances noted in the frequiency doman now convert to-time domain oscillations which may have significace for vulnerability studies.     

The Electromagnetic Field in an EMP Simulator at a High Frequency

The electric field in the working volume of an EMP simulator has been determined experimentally in both amplitude and phase at a frequency that is high enough so that the simulator no longer behaves like a terminated-TEM-mode transmission line. Graphs of the field in the working volume are displayed and interpreted in terms of the TEM and higher parallel-plate modes. The actual field is shown to differ greatly from that characteristic of the TEM mode so that it must be expected that current and charges induced on an obstacle are also very different from those that would be observed if the excitation were an incident plane wave.     

Courant induit par une onde incidente sur un conducteur rectiligne et filiforme situé au voisinage du sol

An analytical result for the current induced by a plane incident wave on a thin straight insulated wire buried in the ground and parallel to the interface is presented. Two methods are presented to solve this problem in the frequency domain; the first one uses the current on an infinite wire; the current induced on a finite wire is obtained adding to the preceding result the reflected currents of different orders. The second uses the reflection coefficients of the transmission line theory. The results are compared with those obtained from another method in which the Sommerfeld integrals are numerically evaluated.     

High-frequency electromagnetic field coupling to long terminatedlines

We present a theory for the EMC problem of electromagnetic field coupling to a long line with arbitrary terminations. The theory is applicable for the high-frequency plane wave electromagnetic field excitations, when the transmission line approximation is no longer valid. Analytical expressions are derived for the induced current along the line, and at the two-line terminals. The coefficients of these expressions are determined using a procedure based on the exact solutions of the integral equation for two similar line configurations, but having a significantly shorter length. The method is, therefore, particularly efficient when considering the electromagnetic field coupling to very long lines. The advantage of the proposed approach is that, in contrast with transmission line approximation, it takes into account high-frequency radiation effects. Furthermore, it allows a considerable reduction in computation time and storage requirements with respect to conventional numerical solutions based on the thin-wire approximation     

Plane-wave diffraction by a wedge--A spectral domain approach

The canonical problem of plane wave diffraction by a wedge in the context of the spectral domain approach which exploits the relationship between the induced current on a scatterer and its far field is investigated. It is shown how the exact solution to the wedge diffraction problem can be manipulated in a form which enables one to interpret the far scattered field as the Fourier transform of the physical optics (PO) current on the two faces of the wedge augmented by the fringe current near the tip of the wedge. A uniform asymptotic expansion for the total field which slightly modifies the Ansatz in the uniform asymptotic theory of electromagnetic edge diffraction is constructed.     

EMP Effects on the Performance of a Direct Sequence Spread-Spectrum Communication System

This paper presents an analysis of the performance of a direct sequence spread-spectrum communication (processor) system operating in a nuclear EMP environment. EMP-induced interference (conducted EMP) at the receiver is modeled by a damped sinusoid and the analysis of the system uses a frequency domain approach instead of the conventional time domain approach. However, the interference suppression factor derived using the frequency domain approach reduces to that obtained using a time domain approach for the tone jammer case, in which the damping factor in the conducted EMP interference model approaches unity. Using a Gaussian approximation to the interference, numerical results are presented to illustrate the significant EMP-induced interference effects on the system performance and its hardening design parameters.     

十字形频率选择表面单元的传输系数分析

传输系数是频率选择表面的一项重要技术指标。简要介绍了利用谱域Galerkin法计算平面频率选择表面传输系数的方法。该方法以平面波谱展开和傅里叶变换为基础,通过矩量法求解频率选择表面电流,进而求得传输系数。对一个十字形频率选择表面的传输系数进行了测量和计算,并将测量结果和计算结果进行了比较,两者吻合得较好,验证了本方法的正确性。