On bounding the excitation of a terminated wire behind an aperture in a shield

A formulation is developed for determining the voltage and current induced on an impedance-terminated wire behind an aperture in a shield. Loading effects on the aperture are included by using receiving antenna theory. Upper bounds for the current and voltage are obtained and numerical results are presented for a thin slot antenna.     

Radar waveform synthesis method--A new radar detection scheme

A new scheme for radar detection and discrimination, the radar waveform synthesis method, is investigated. This scheme consists of synthesizing the waveform of an incident radar signal which excites the target in such a way that the return radar signal from the target contains only a single natural resonance mode of the target. When the synthesized incident radar signal for a known preselected target is applied to a wrong target, the return radar signal will be significantly different from that of a natural mode of resonance, thus the wrong target can be sensitively discriminated. A simple geometry of a thin wire illuminated by a radar signal at normal incidence has been studied. The induced current on the target and the backscattered field from the target are obtained in terms of natural resonance modes. The required waveforms for the incident radar signal for exciting return radar signals which contain various single natural mode of resonance are obtained. When an incident radar signal synthesized to excite a natural resonance mode of a thin wire is applied to a slightly shorter or longer thin wire, the return radar signal from the wrong target is shown to be significantly different from that of a pure natural mode of resonance.     

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 an incident wave on a thin straight wire located in the vicinity of 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 solution the reflected currents of different orders. The second uses the reflection coefficient of the transmission line theory. The results are compared with those obtained from another method in which Sommerfeld integrals are numerically evaluated.     

Time harmonic solutions for a long horizontal wire over the ground with grazing incidence

A parametric study of the current responses on a long horizontal wire over the ground with frequencies ranging from 10 kHz to 100 MHz, earth conductivities of10^{-1}, 10^{-2}, and10^{-3}S/m, and wire heights of 10, 5, and 1 m. These current responses for typical wire lengths are given for a grazing incident plane wave and an incident lateral 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.     

Currents induced in a wire cross by a plane wave incident at an angle

The currents induced in a thin-wire cross with equal mutually perpendicular arms by an incident plane electromagnetic wave are determined when the normal to the wave front is perpendicular to the horizontal wire and is at an anglethetawith respect to the vertical wire; the direction of the electric vector in the wave front is arbitrary. The analysis is formulated in general terms but explicit formulas are obtained only for the zero-order currents which are generally adequate to determine the scattered field of very thin wires. The relatively simple formulas consist of even and odd parts for both the vertical and horizontal wires; they include components due to mutual coupling as well as those excited directly by the incident field.     

Reflector aperture-blocking by a loaded wire feed

A technique for computing the total aperture-blockage effect of a loaded wire antenna feeding a paraboloidal reflector is described. First an analytical formulation for determining the fields scattered by a field incident upon a loaded wire antenna is described, and then an iterative procedure utilizing this result to obtain the aperture blockage effect is given. Typical results are presented for both simple and complex feed structures.     

Cramér-Rao bound for multiple parameters estimation using a polarization sensitive array

In this paper, new Cramér-Rao lower bounds (CRB) of the estimates of frequencies, two-dimensional arrival angles and polarization parameters of multiple incident signals are derived for a polarization sensitive array. The incident sources have distinct carrier-frequencies, in contrast to the modeling of all sources to be at the same known carrier-frequency, which has been investigated in the existing research literature on the Cramér-Rao bounds (CRB) for polarization sensitive direction finding. The derived CRBs are compact closed-form expressions and applicable to an arbitrary array geometry. Numerical examples and analysis of some special cases provide insights into the fact that the estimation accuracy of all parameters is enhanced with the increasing signal-to-noise ratio (SNR) and number of snapshots. In addition, they are hardly influenced by the sampling frequency and independent of the initial phase of incident sources. These insights offer guidelines to the system engineer on how to improve parameters’ estimation accuracy.     

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.     

A stabilized resistive voltage source for FDTD thin-wire models

The von Neumann analysis is applied to investigate the stability of a source connected on a wire described by a thin-wire model. Both a soft source and a resistive voltage source (RVS) are shown to limit the stable range of values for wire radius or time step. Using the von Neumann analysis, a stable RVS model for thin wires is developed. The proposed model is verified by comparison with a hard source, an original RVS and NEC-generated reference data. The stabilized RVS introduces no additional stability constraints on those of the wire model while maintaining fast decay of incident fields of the original RVS model.     

Electromagnetic excitation of a wire through an aperture-perforated conducting screen

Integro-differential equations are formulated for the general problem of a finite-length wire excited through an arbitrarily shaped aperture in a conducting screen. The wire is assumed to be electrically thin and perfectly conducting, and it is arbitrarily oriented behind the perfectly conducting screen of infinite extent. A known, specified incident field illuminates the perforated-screen/wire structure. The integro-differential equations fully account for the coupling between the wire and the aperture/screen. They are specialized to the case of the wire parallel to the screen with the aperture a narrow slot of general length. These special equations are solved numerically and data are presented for wire currents and aperture fields under selected conditions of wire/slot lengths and orientation. Data indicative of the coupling between the wire and slot are presented.     

Green's function technique for near-zone scattering by cylindrical wires with finite conductivity

With a technique not requiring matrix inversion, the current distribution induced on a straight thin wire by an incident plane wave or a nearby sinusoidal dipole is determined. The wire may have any length exceeding0.05lambdaand any finite conductivity such that the radius is equal to or greater than the skin depth.     

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。     

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     

On the prediction of digital circuit susceptibility to radiated EMI

The effects of radiated radio-frequency interference (RFI) on the operation of digital systems are studied by simulating the response of simple logic circuits to incident plane waves. The simulation is accomplished by combining a linear electromagnetic moment-method model of the wire structure with a nonlinear circuit model of the solid-state components. The complete model is analyzed in the linear and nonlinear regimes as an example. It is shown how a circuit simulator, such as SPICE, can be used in the analysis of an arbitrary wire network loaded with logic circuits, by the process of representing the linear wire network as a lumped-element N-port π network and interfacing it to the nonlinear circuit simulator. Examples are given that demonstrate the occurrence of both static and dynamic failures under various RFI-field excitations and wire structure geometries. The prediction methods presented in this paper, can be used by EMC engineers to assess the likelihood of failures in RFI-exposed digital systems,     

电磁脉冲斜入射时无限长近地细导线表面电流的计算

本文应用时域有限差分（FDTD）方法研究电磁脉冲斜入射下无限长细导线的表面感应电流,并考虑了有耗地面的影响,该问题可以转换为二维问题来计算,从而大大节约计算资源,文中给出了各种情况下的感应电流计算结果。     

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     

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.     

Current induced by a plane wave on a thin infinite coated wire above the ground

The current induced on a thin infinite coated wire above the ground when an electromagnetic plane wave is incident on it is calculated. The final result is presented in a form which exhibits clearly the various contributions to the total impedance of the wire-ground system. Numerical examples are given which demonstrate the dependence of the induced current on the conductivity of the ground, the thickness of the coating, and the polarization and direction of propagation of the incident wave.     

A Frequency Selective Surface With Miniaturized Elements

We demonstrate a new class of bandpass frequency selective surface (FSS), the building block of which, unlike the traditional FSSs, makes use of resonant dipole and slot structures that have dimensions much smaller than the operating wavelength. This design allows localization of bandpass characteristics to within a small area on the surface which in turn facilitates flexible spatial filtering for an arbitrary wave phasefront. The proposed FSS is made up of periodic array of metallic patches separated by thin air-gaps backed by a wire mesh having the same periodicity (Ltlambda). The array of metallic patches constitute a capacitive surface and the wire mesh a coupled inductive surface, which together act as a resonant structure in the path of an incident plane wave. Like traditional FSSs, the capacitive and inductive surfaces of the proposed FSS can easily be fabricated using printed circuit technology on both sides of microwave substrates. It is shown that by cascading such bandpass surfaces in a proper fashion, any arbitrary multipole filter or non-commensurate multiband response can be obtained. The frequency response of the proposed miniaturized-element frequency selective surface (MEFSS) is demonstrated for various incident angles and it is shown that one-pole designs are less sensitive than two-pole designs to the angle of incidence. Dual band designs are also possible based on two-pole designs, but are more sensitive to incident angle than single band designs because of their larger (in terms of wavelengths) spacing. Prototypes of single-pole and dual-pole MEFSSs are fabricated and tested in a waveguide environment at X-band frequencies and excellent agreements between the measured and simulated results are demonstrated