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     

Calculation of external aperture admittance and radiation patternof a narrow slot cut across an edge of a sectoral cylinder in terms of aspectrum of two-dimensional solutions

A slotted triangular cylinder is a candidate for a base station antenna in mobile communications. This paper presents an analysis of the external aperture admittance and the radiation pattern of a transverse narrow slot cut across one of the wedges of a sectoral cylinder, the cross section of which approximates the actual triangular shape. Thereby, the external region can be described in terms of two canonical shapes, for which the dyadic Green's functions are obtained analytically. The aperture admittance of the slot is expressed in terms of the integrals of magnetic current over the slot aperture and the infinitely extended interface of the canonical regions. These integrals are evaluated in the spacial and spectral domains, respectively. This hybrid analysis provides good convergence of the results. The dependence of the 3-dB beamwidth and the front to back ratio of the transverse radiation pattern from the slot upon the size and the sector angle of the cylinder are also presented     

Electromagnetic scattering from three-dimensional cavities via aconnection scheme

The electromagnetic scattering from arbitrary three-dimensional cavities is presented. To alleviate computational constraints for three-dimensional problems, a connection scheme is developed based on microwave network theory. This scheme allows the cavity to be divided into sections and each section to be analyzed independently of the rest of the cavity. Each section of the cavity is represented by a generalized admittance matrix which if formulated via a boundary-integral equation approach. Using the concept of input and load admittance, the aperture admittance matrix of the cavity can be derived by cascading the admittance matrices of individual sections. Once the cavity aperture admittance matrix is obtained, the aperture electric field and the backscattered field are found by the standard generalized network formulation. Numerical results are compared against modal solutions of regularly shaped cavities with good agreement. This connection scheme leads to a reduction in computational resources, especially for cavities with one dimension much larger than the other two     

边界积分法及连接算法分析任意腔体的散射

本文利用边界积分法分析二维任意腔体的散射,给出一种基于微波网络原理的连接算法,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,然后利用连接算法将各段连接,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等效磁流及后向散射场。本文方法可作为一种机辅设计算法。     

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。     

Aperture admittance of a rectangular aperture and its use

It has been found that a rectangular aperture not more than one wavelength long in a conducting plane can be characterized by two complex numbers (called the aperture admittances) for the regions on each side of the aperture for the purpose of obtaining an accurate estimate of the tangential electric field inside the aperture. To define these admittances, the aperture is closed with an infinitesimally thin perfectly conducting plate. The aperture admittance for the region on one side of the aperture is that of the magnetic current sheet M₀ placed on this side of the plate. The aperture admittance for the region on the other side of the aperture is that of M₀ placed on the other side of the plate. M₀ is parallel to one of the long edges of the aperture, and along this edge is a simple half-cycle of a sinusoid. M₀ is independent of the coordinate that is measured along the width of the aperture     

On the Pulse Response of a Flush-Mounted Coaxial Aperture

The radiation field pattern of a flush-mounted coaxial aperture is derived in the frequency domain. By using the Lorentz reciprocity theorem, the equivalent current generator is obtained which drives the apparent annular antenna admittance in shunt with the load admittance. The current source, aperture admittance, and load admittance determine the transfer function. The transfer function multiplied by the expression for the spectrum of the incident pulse forms the integrand of the Fourier transform from which the time history of the current waveform in the load admittance may be obtained using a computer. There are several applications of the theory. The one of dominant interest at present may be described as follows. A coaxial transmission line terminated in a known load admittance is located in the interior of a missile. The free end of the cable forms an aperture antenna at the skin of the missile, i.e., at the normal junction of coaxial connectors. The problem is to determine the time history of the current in the load admittance when an intense transient electromagnetic field impinges on the receiving antenna. Very accurate numerical results may be obtained from this theory provided the ground plane is sufficiently large and certain dimensional limitations on the sizes of the inner conductor and sheath of the coaxial aperture (expressed in terms of the wavelength) are met.     

CADMIC---Computer-Aided Design of Microwave Integrated Circuits

A computer program for the analysis and design of distributed lumped circuits, including microwave integrated circuits, is discussed. It is capable of frequency-domain analysis, optimization of transducer power gain, reflection coefficient, and/or noise figure. Also, the program can compute the return difference with respect to any admittance parameter so that the stability of the circuit can be determined by the Nyquist criterion. The program handles complex impedances, resistors, capacitors, inductors, transmission lines, independent current sources and grounded voltage sources, voltage-controlled current sources, and multiport elements, such as transistors and circulators, described by their scattering or admittance parameters. It contains a free-format input. The implementation is based on the indefinite admittance matrix, sparse matrices, adjoint networks, the Fletcher-Powell or Fletcher minimization algorithm, and Bode's feedback theory.     

The Annular Slot Antenna in a Lossy Biological Medium (Short Papers)

An integral equation is formulated for a coaxially fed annular aperture antenna. The integral equation in terms of the unknown tangential aperture electric field is solved numerically by the Method of Moments. The coaxial feed line is air filled while the exterior region consists of i) air, ii) fat or bone, and iii) muscle. Results are given for the aperture electric field, apparent input admittance, and contours of constant power absorption when the excitation frequency is 2.45 GHz.     

A general expression of dyadic Green's functions in radiallymultilayered chiral media

A general expression of spectral-domain dyadic Green's function (DGF) is presented for defining the electromagnetic radiation fields in spherically arbitrary multilayered and chiral media. Without any loss of the generality, each of the radial multilayers could be the chiral layer with different permittivity, permeability, and chirality admittance, while both distribution and location of current sources are assumed to be arbitrary. The DGF is composed of the unbounded DGF and the scattering DGF, based on the method of scattering superposition. The scattering DGF in each layer is constructed in terms of the modified and normalized spherical vector wave functions. The coefficients of the scattering DGFs are derived and expressed in terms of the equivalent reflection and transmission coefficients, by applying boundary conditions satisfied by the coefficient matrices     

导电平板上任意孔缝的TM波散射及传输特性分析

该文利用边界积分法分析导电平板上任意孔缝的TM波散射及传输特性,并引入了一种基于微波网络原理的连接算法以缓解计算机内存对所计算孔缝尺寸的限制。首先将孔缝内腔分为几段,用积分方程法分别计算每段的广义导纳矩阵,然后利用连接算法将各段连接起来得到整个孔缝的口径导纳矩阵,最后由广义网络原理求解孔缝的等效磁流、后向散射场以及传输系数。     

多端口耦合问题的等效导纳矩阵

本文提出了一种处理多端口耦合问题的有效方法。在该问题中,各端口波导分别通过一耦合孔与耦合区进行耦合。利用矩量法,首先导出了多端口耦合问题的关于传输模和截止模的等效导纳矩阵的计算公式。在此基础上,考虑到截止模加载于端口波导的特性阻抗,经过适当的矩阵运算,得到仅仅关于传输模的等效导纳矩阵。用此方法计算了一个 H 面 T 形接头的等效导纳矩阵和等效电路参数,所得结果与文献[1]们的结果非要吻合。     

The Variational Treatment of Thick Interacting Inductive Irises

The problem of two thick interacting inductive irises in waveguide is treated with a variational approach. Using the appropriate Green's functions in the continuity equations of the transverse magnetic fields yields two coupled integral equations for the magnetic currents on the apertures. Solving one equation by Fourier expansion and introducing in the remaining equation, a variational expression for the driving-point admittance is obtained. This is treated with a Rayleigh-Ritz procedure and matrix methods, avoiding the explicit computation of field amplitudes. The analysis is carried out in terms of an eigenmode expansion, as well as in terms of an expansion a la Schwinger on the aperture and the features of the two methods are contrasted. In spite of its somewhat greater mathematical complexity, the latter generally provides a superior solution for a given order of the trial field. In both cases the solutions are very accurate, uniformly convergent to their common limit value, and require manipulations with small-order matrices only. The agreement with the experiment is excellent.     

广义网络法分析复杂孔缝耦合问题

本文利用广义网络法结合连接算法分析复杂孔缝耦合问题.首先根据孔缝的结构及填充特点将其内腔体分为适当的几段,利用边界元法分别计算每段的广义导纳矩阵,再借助连接算法将各段连接起来得到整个孔缝的口径导纳矩阵,最后由广义网络法求解孔缝的口径磁流、散射及传输场.该方法不仅在计算效率方面取得了较大突破,也使复杂填充孔缝的分析得到很大简化.     

The admittance of a parallel-plate waveguide aperture illuminating a metal sheet

The admittance of a parallel-plate waveguide aperture having an infinite flange and illuminating a metal sheet is determined by two separate methods: 1) wedge diffraction theory; 2) an integral transform solution. Numerical computations obtained by either method are in excellent agreement and are verified experimentally. A Smith chart is employed to show that, for a given aperture width, the admittance locus coalesces about the half-space value as the metal sheet recedes to infinity. A strong interaction between the aperture and the metal sheet occurs for distances in the vicinity of integral multiples of one half-wavelength. The interaction becomes much more localized with respect to distance as the distance to the sheet is increased; however, the admittance is always infinite at these distances.     

Mutual coupling between log-periodic antennas

Numerical techniques are used for the analysis of mutual coupling in arrays of log-periodic dipole antennas. The analysis is formulated in terms of impedance and admittance matrices for the dipole and transmission line networks. Approximations are made to allow the solution for moderately sized arrays to be practical with the existing generation of computers. Antenna patterns for the array are expressed in terms of the current incident on each log-periodic antenna. Results are presented for systems of one, two, and three log-periodic antennas.     

Modeling Rectangular Waveguide Junctions by the Eigenfunction Method

A method to determine the impedance and admittance matrices of a certain class of rectangular waveguide junctions is presented. First, general matrices are obtained relating all of the modes that may exist in the waveguides connected to the ports, The expressions for the matrix entries are given in terms of the eigenfunctions of the volume occupied by the junction and the fields at the ports. Second, to obtain a relationship between the propagating modes of the connecting waveguides, a numerical iterative procedure is developed to eliminate the evanescent modes from the general matrices. Practical applications have shown that the results agree well with the previous ones, and the method can readily be used to analyze different types of junctions in any required frequency range.     

Theory of a multiply fed and loaded insulated linear antenna in air

Analytic expressions are derived for the input admittance and the current distribution along the multiply fed and loaded insulated antenna in air which is excited across feed gaps of nonzero widths. The Wiener-Hopf type analysis for a center fed insulated antenna is combined with the axial field discontinuity (AFD) method to develop the current and admittance expression. This AFD method considers the metallic surface of the linear antenna as a series combination of longitudinal, electric-field surface functions that exist due to feeding and/or loading. The analysis, which does not employ superposition of even and odd distributions of sources and loads, yields final expressions in terms of the excitation location, its aperture electric field within the feed gaps, impedance locations, and their values. The current distribution for cases of unity dielectric constant shows an excellent agreement with data based on the moment method. The input admittances and current distributions are reported for different multiple excitations and loads and dielectric constants of the insulator     

Absorbing boundary conditions for the finite-element analysis ofplanar devices

The finite-element method is used to determine the scattering matrices of open devices in two dimensions. Microwave and optical devices in which the fields are not confined to a finite region can be analyzed with the finite-element method if special boundary conditions are used to absorb outgoing radiation. The absorbing boundary conditions can be imposed by the addition of two terms to the usual functional for the scalar Helmholtz equation. Universal matrices are introduced to allow the additional terms to be easily assembled, for polynomial orders one through four. Results are given for the impedance of a parallel-plate waveguide radiating into free space and for the scattering parameters of three dielectric slab waveguide devices: a rectangular discontinuity, a feed structure, and a junction     

Input admittance and complete near-field distribution of an annular aperture antenna driven by a coaxial line

An annular aperture antenna driven by a coaxial transmission line is studied. An analytical and closed-form expression for input admittance is obtained. The effect of all higher order TMonto the admittance is found to be quite significant. Aperture field distribution is expressed in terms of the TEM and the first five TMonmodes. Higher order modes at the aperture can be estimated from the edge behavior. Near-field distribution based upon these modes is then cast into a form suitable for numerical evaluation.