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.     

Low-Frequency Electromagnetic Penetration of Loaded Apertures

Low-frequency (quasi-static) electromagnetic penetration of an aperture can be reduced by loading the aperture with a conductive film or a bonded-junction wire mesh. A quantitative analysis of this phenomenon is carried out in this paper for a loaded circular aperture in a perfectly conducting ground plane of infinite transverse extent. Contact resistance between the aperture loading and the rim is taken into account. The quasi-static magnetic-field problem and the electrostatic field problem from which the aperture polarizabilities and penetrant fluxes are determined are shown to reduce to the problem of solving a single Fredholm integral equation. Exact (numerical) and approximate (variational) solutions to this integral equation are obtained, and the latter are used to represent the polarizabilities and penetrant fluxes by simple analytical formulas and equivalent circuits. These representations are found to be quite accurate when the contact resistance is not too large     

Electromagnetic transmission through mesh covered apertures and arrays of apertures in a conducting screen

The problem of electromagnetic transmission through wire mesh covered arbitrarily shaped aperture or arrays of apertures (possibly covered by a thin lossy dielectric sheet) in a perfectly conducting ground plane is considered. The equivalence principle and image theory are used to derive an integral equation for the equivalent magnetic currents. The method of moments is utilized to solve the integral equation, with the aperture modeled by triangular patches. Numerical results are presented for transmission coefficients and transmission cross-section patterns for electrically small apertures.     

Matching of equivalent field regions

In aperture problems, integral equations for equivalent currents are often found by enforcing matching of equivalent fields. The enforcement is made in the aperture surface region adjoining the two volumes on each side of the aperture. In the case of an aperture in a planar perfectly conducting screen, having the same homogeneous medium on both sides and an impressed current on one side, an alternative procedure is relevant. We make use of the fact that in the aperture the tangential component of the magnetic field due to the induced currents in the screen is zero. The use of such a procedure shows that equivalent currents can be found by a consideration of only one of the two volumes into which the aperture plane divides the space. Furthermore, from a consideration of an automatic matching at the aperture, additional information about tangential as well as normal field components is obtained. We compare the two procedures in this tutorial article.     

Transient current on a wire penetrating a cavity-backed circular aperture in an infinite screen

The problem of a wire penetrating a circular aperture in an infinite conducting screen and entering a circular cylindrical cavity is considered. Results for the transient current propagating along the wire both inside and outside the cavity are presented. The current in both regions is evaluated in the frequency domain by the method of moments (MOM). An approximate method for evaluating the exterior current at an observation point far from the aperture is discussed. To obtain the transient response, a numerical inverse Fourier transform is used. The current response is examined as a function of cavity and aperture dimensions. Results obtained with the approximate method are compared with the MOM solution. It appears that information concerning the interior cavity dimensions is present in these exterior observations.<>     

导电平面上三维任意腔体的散射分析

本文利用边界积分法及连接算法分析导电平面上的三维腔体散射。在引入广义导纳矩阵后,可将腔体分为几段,分别用积分方程法计算每段的广义导纳矩阵。然后利用连接算法得到整个腔体的口径导纳矩阵。最后由广义网络原理求解腔体的口径等效磁流及后向散射场。本文方法极大地缓解了计算机内存对腔体尺寸的限制,提高了分析效率,可作为一种机辅设计算法。     

Characteristic modes of a rectangular aperture in a perfectlyconducting plane

The objective of the paper is the analysis of a rectangular aperture in a perfectly conducting plane using the characteristic mode theory. The problem is first formulated as an operator equation involving the continuity of the tangential components of the magnetic field in the aperture region. The operator equation is used, with the help of the moment method, to determine the eigenvalues, eigencurrents, and the characteristic magnetic currents of the aperture. When these modes are determined, the equivalent magnetic current and other parameters of interest can then be obtained     

An approximate solution for E-polarization coupling into acoaxial cylinder with an infinite axial slot

An approximate solution is derived for determining the total current induced on a centrally located conducting wire within a two-dimensional axially slotted cylinder for the case of E-polarization. Its validity is tested against a full moment-method numerical solution of the describing integral equation. The derivation of the approximate solution is similar to the hollow-cylinder case presented by P.M. Morse and H. Feshbach (195) in that the same basic form for the aperture distribution is assumed. A rapidly converging series solution is developed which is shown to be valid for an electrically `narrow' slot (accurate for apertures up to one wavelength wide) over a rather broad frequency spectrum. Though the aperture must be electrically narrow, many practical coupling problems of interest can be accommodated. Useful insight into coupling phenomena is obtained by direct inspection of the solution, and some novel observations about the current response are made     

A numerical solution for the near and far fields of an annular ring of magnetic current

A simple method for calculating the near and far zone fields from an annular ring of circumferentially directed magnetic current which may be used to represent coaxial apertures is presented. Near-field contours are given for two ring sizes. The utility of the method has been illustrated by its application in several practical antenna problems where the magnetic ring current serves as the primary source. Among these are the analysis of dipole antennas mounted on a conducting sphere or cylinder, the impedance of a coaxially fed Yagi-Uda antenna, a coaxially driven wire loop, and the radiation from a coaxial aperture at the base of a cone.     

Analysis of a cylindrical antenna containing an aperture coupledload

In this paper we present the basis for the analysis of shielded tuning networks coupled to wire antenna elements. The structure analyzed comprises three conducting cylindrical tubes that form an aperture-fed circular coaxial waveguide. Two methods are presented for formulating and solving integral equations for the structure. The first method is based on the mixed potential electric field integral equation enforced on the three cylindrical tubes, and the second is based on aperture theory. An end correction capacitance is used to adjust the reflection coefficient in the eigenmode expressions of the aperture method. The data obtained by the two methods are in close agreement. Differences in actual currents and equivalent currents obtained from solutions are discussed and reconciled     

Electromagnetic scattering from and transmission through arbitraryapertures in conducting bodies

The general 3-D aperture coupling problem is formulated in terms of an integral equation for the equivalent magnetic current in the aperture, which is numerically solved by the method of moments. The aperture is characterized by two aperture admittance matrices, one for the exterior region and the other for the interior region. These two admittance matrices are determined separately but in a similar manner if the pseudo-image method is used. Numerically workable expressions are developed for the two aperture admittance matrices by decomposing each of them into a half-space admittance matrix and a supplementary admittance matrix. The half-space admittance is relatively easy to compute and has been investigated in the literature. The supplementary admittance matrix is expressed in terms of the generalized impedance combining the existing numerical codes for an arbitrarily shaped scatterer and for an arbitrary aperture in a conducting plane, one can obtain a code which is especially designed for an arbitrary aperture in a conducting surface of arbitrary shape     

Scattering from and penetration into a dielectric-filled conductingcylinder with multiple apertures

The theory of characteristic modes for aperture problems is used in this paper to solve the equivalent magnetic current and aperture fields due to a conducting cylinder with multiple slots. It is assumed that these slots are illuminated by either a transverse electric (TE) or a transverse magnetic (TM) plane wave and the media inside and outside the cylinder exhibit different electromagnetic properties. The formulation is given for the general case and numerical results for a limited number of slots are presented     

Coupling through narrow slot apertures to thin-wire structures

Electromagnetic coupling through a narrow slot aperture in an infinite ground plane is considered when a thin wire is present in the coupled half-space. The effect of the wire on coupling is determined. The slot has width and depth. The method of moments is applied to determine equivalent aperture currents and wire currents. Then coupling is calculated from the resulting fields. Results are presented for high and low Q slots and on and off resonance     

Electromagnetic excitation of a thin wire: a traveling-waveapproach

An approximate representation for the current along a perfectly conducting straight thin wire is presented. The current is approximated in terms of pulsed waves that travel along the wire with the velocity of the exterior medium. At the ends of the wire, these pulses are partially reflected, with a constant reflection coefficient and delay time. Subsequently, the traveling-wave representation for the current is used to derive an approximate expression for the electric field outside the wire that is caused by this current. For voltage excitation, this expression contains only closed-form contributions. For plane-wave excitation, the expression contains a single integral over the initial pulse that must be computed numerically. Although the expression obtained is essentially a far-field approximation, it turns out to be valid from distances of the order of a single wire length. Results for a representative choice of wire dimensions and pulse lengths are presented and discussed     

带光阑的复杂光学系统的焦移

根据Collins公式,导出了球而波经带有后继光学系统的硬边光阑衍射的焦移公式,并给出了等效的变换矩阵。光阑的作用可等效为一个具有可变焦距的“薄透镜”。     

Characteristic Modes for Aperture Problems

A theory of characteristic modes is developed for problems consisting of two regions coupled by an aperture. The modes are derived from a weighted eigenvalue equation whose eigenfunctions define a set of real expansion functions for the equivalent magnetic current over the aperture region and whose eigenvalues are the modal aperture admittances. A modal solution is obtained for an aperture of arbitrary size and shape coupling two regions of arbitrary size and shape. The theory provides a rigorous basis for the augmentation of the Bethe-hole theory by radiation conductance terms, for its extension to apertures of larger electrical size, and for its extension to apertures in nonplanar conducting surfaces.     

Common‐Mode Current on a Wire through a Corrugated Aperture

This paper investigates the effect of a corrugated aperture on a common‐mode current traveling along a penetrating wire. Computational results illustrate that the corrugated aperture acts as a filter, significantly reducing the common‐mode current on the wire. This effect causes a reduction of radiated emission from cables passing through apertures on shielding enclosures. To predict and analyze the characteristics of the common‐mode current on a straight wire passing through a corrugated aperture with cylindrical symmetry, the finite‐difference time‐domain (FDTD) method is applied.     

On the electromagnetic scattering from infinite rectangular grids with finite conductivity

-The development of a new numerical technique for the analysis of electromagnetic scattering from a rectangular wire (or strip) mesh. According to this technique the conjugate gradient method (CGM) and the fast Fourier transform (FFT) are used to solved for the aperture fields and the induced current densities. The method is efficient because 1) it makes use of the fast Fourier transform, 2) it converts a set of integrodifferential equations into a set of algebraic equations, and 3) it does not require inversion of any matrices. Unlike the moment method, the spectral iteration approach (SIT), and the averaged boundary conditions method, this technique can be used for arbitrary size and spacing between adjacent strips. The equivalent radius principle is used to determine the reflection coefficient from a wire mesh. Results, examples, and comparisons of this method with other methods support the validity of the algorithm.     

Characteristic modes of a slot in a conducting cylinder and theiruse for penetration and scattering, TE case

A characteristic mode theory for slots in a circular conducting cylinder is given for calculating the characteristic magnetic currents, the equivalent magnetic current, the radiation patterns, and the fields everywhere (especially in the aperture region) of an infinitely long thin perfectly conducting cylinder with an infinitely long slot. The characteristic modes are obtained from the solution of an eigenvalue equation representing the continuity of the tangential component of the magnetic field in the slot     

Resistive and conductive tube boundary condition models formaterial wire-shaped scatterers

An equivalent boundary condition model is introduced for computing the scattering by material wire-shaped scatterers which are either dielectric or magnetic, but not both simultaneously. While the methodology for numerically computing the scattering by perfectly conducting thin-wire scatterers has been developed for decades, no simple model for material scatterers with large length-to-radius ratios (wire shapes) has been available. This new model can be easily integrated into existing thin-wire computer codes while adding virtually no computational burden. Validating results are shown using comparisons of the full-wave scattering from a number of thin wire-shaped dielectric and magnetic structures with this new equivalent boundary condition model. It is demonstrated that this model is, in essence, an extension of the internal impedance expression for a conducting wire (developed over 50 years ago) to simple-material wire-shaped scatterers possessing a very wide range of material parameters