Excitation of a grounded dielectric slab by a horizontal dipole

The structure consisting of a horizontal electric dipole above a grounded dielectric slab is examined, primarily from the standpoint of power distribution among the two power-carrying wave components, i.e., surface and space waves. It is shown that surface wave propagation is always in the form of two distinct modes characterized by the same cutoff properties. Also, surface wave excitation efficiency curves are given for a range of parameter variation.     

Analysis and design of a leaky-wave EMC dipole array

An analysis of an electromagnetically coupled (EMC) dipole array is presented, in which a microstrip line is coupled to an infinite periodic linear array of microstrip dipoles, arranged perpendicular to the line. The spectral-domain immittance method is used to obtain the periodic Green's function for the two-layered structure, and the method of moments with a Galerkin testing procedure is then used to enforce the electric field integral equation (EFIE) on the line and the dipole within a unit cell of the structure to obtain the determinantal equation for the unknown leaky-wave propagation constant. One of the interesting features of this analysis is the path of integration in the complex plane used to compute the moment method reactions, which must be partly on the improper sheet for the m=-1 space harmonic when it radiates in the forward direction. Measured radiation patterns for a 10-element EMC dipole array are presented and compared with the corresponding theoretical ones     

Surface potentials of stratified spheroidal volume conductors excited by an electric dipole source

An exact solution for the surface potentials produced by a dipole source surrounded by a stratified prolate (or oblate) volume conductor is given. A transmission matrix approach is used which permits the surface potentials to be calculated using a simple iterative method. The computer implementation of the method is discussed     

Scattering from a conductive rectangular plate covered by a thickdielectric layer and excited from a dipole source or a plane wave

The scattering of electromagnetic radiation from a conductive rectangular plate of infinitesimal thickness covered by a dielectric parallelepiped of arbitrary size is analyzed. An integral equation formulation is employed in terms of the electric field inside the dielectric layer and the surface current density on the conductive plate, and is solved approximately by using entire domain Galerkin technique. The electric field inside the dielectric layer is described in terms of a superposition of exponential waves while, in describing the surface current density on the conductive plate, two types of entire domain basis functions are utilized: either Fourier-exponential series or Chebyshev series type finite-term expansions are employed alternatively. Numerical results are computed and presented for several scatterer sizes and excitation types     

Radiation from a dipole in the proximity of a general anisotropic grounded layer

The radiation from a dipole in the presence of a grounded general gyromagnetic-electric (gyrotropic) layer is investigated. The use of matrix methods in conjunction with Fourier transformation techniques greatly facilitates the formulation of the boundary-value problem, reducing the algebraic complexity to a minimum, and provides a closed-form representation of the electromagnetic field over the anisotropic region. Numerical results in plots, related to the radiation pattern of the structure, are also included for various cases.     

Radiation characteristics of dipole antenna in a grounded composite magnetized semiconductor plasma

The radiation characteristics of dipole antenna in a grounded nonreciprocal semiconductor plasma are examined using the spectral domain-exponential matrix technique, and such solid plasma is taken as GaAs material. The effects of constitutive and geometrical parameters of the semiconductor plasma on the radiation patterns are demonstrated in detail, and the results show that the far-field behaviour of dipole antenna can be changed by adjusting both the operating frequency and the applied magnetic field, et al.     

Radiation from a dipole in the presence of a grounded arbitrary magnetized chiroferrite slab

The radiation characteristics of a dipole antenna placed on a grounded chiroferrite slab are investigated, and the theoretical treatment is based on the method of generalized spectral domain-exponential matrix. Numerical calculations are performed for the three-dimension far field distributions of dipole and the combined effects of chirality and gyrotropy are taken into consideration. Our study is an initial step for the application of chiroferrite materials to microstrip antenna.     

Resonant-cavity technique for the measurement of leaky-wave complex propagation coefficients

A resonant-cavity technique for the measurement of k/? diagrams (dispersion relations) of leaky-wave structures is discussed. Theoretical calculations and measured results are presented for a specific structure of the class of leaky-wave structures considered. The extension of this technique to more general smooth and periodic structures is indicated.     

Propagation of EM pulses excited by an electric dipole in aconducting medium

Exact solutions are given for the transient electromagnetic (EM) fields excited by an electric dipole antenna with an impulsive current in a conducting medium. There exists an optimum waveform for the antenna current which can generate an EM pulse with a maximum intensity at a particular distance from the antenna. It is found that the EM fields of an EM pulse excited by an antenna in a conducting medium can be divided into two parts. The first part is an impulse wave which propagates with the speed of light (1/√(μϵ)) and decays exponentially. The second part builds up gradually and propagates slowly, and more importantly this part attenuates as an inverse power of distance which is a much slower rate than an exponential decay     

Time-domain analysis of propagation in inhomogeneous anisotropiclossy slabs

An equivalent-transmission-line-circuit (ETLC) model is developed to discuss the transient propagation problem of a plane wave in inhomogeneous, anisotropic, and transversely lossy slabs. This model is based on the analogy between the field equations and the coupled transmission line equations. By establishing the analogy, suitable lumped-circuit models are proposed to treat the equivalent transmission lines, which may then be solved by the circuit simulation program. In this study, the accuracy and convergence of the lumped-circuit models are examined. The ETLC model is then applied to discuss the propagation problem in anisotropic graphite/epoxy laminates with numerical results presented to show the transient responses due to the electromagnetic pulse and Gaussian pulse     

Wave propagation in a 1D magnetophotonic crystal formed from a nanoporous metamaterial

Formation of the eigenmodes of a 1D magnetophotonic crystal formed from a metamaterial (a nanoporous magnetooptical matrix whose pores are filled with a negative-permittivity metal) is studied. It is shown that the magnetooptical properties are not suppressed by strong local anisotropy and, while the metamaterial supports only one propagating mode, the photonic crystal supports propagating modes with both polarizations.     

Effects of a dielectric coating on leaky-wave long-slot waveguideantennas

A theoretical and experimental study is made of the effects of a dielectric of arbitrary thickness, permittivity, and loss tangent upon the aperture field distributions and the far-field radiation pattern characteristics of long-slot leaky-wave antennas cut on the broadwall of a rectangular waveguide and mounted in an infinite ground plane. The relevant integral equations for determining the aperture fields are developed and then solved using the moment method. Expressions for the far-field radiation patterns and isolation responses are developed. Calculated and experimental results for several antennas are presented and discussed     

Wave propagation and dipole radiation in a suddenly created plasma

Propagation and radiation of electromagnetic waves from oscillating sources in a suddenly created plasma are studied in this investigation. Field expressions are derived through the use of Laplace transformations. The spatial distribution of sources is taken to be arbitrary but confined. Two cases are considered in detail: 1) plane wave propagation in a source-free region and 2) electric point dipole radiation. In the case of plane wave propagation, various aspects such as wave split, frequency shift, phase and group velocities, amplitude changes, power flows, and energy relations are discussed. In the case of electric dipole radiation, the electromagnetic fields and instantaneous radiated power are calculated and expressed in terms of Lommel functions of two variables. Asymptotic expressions and graphical results of numerical calculations of these quantities are presented. Many interesting properties of the spherical waves and power radiation are discussed.     

Comparison of asymptotic solutions for the surface field excited by a magnetic dipole on a cylinder

In the analysis of mutual coupling in apertures on a convex surface, the surface field due to a magnetic dipole on a large conducting cylinder is an important canonical problem. Over the years a number of approximate asymptotic solutions have been described in the literature. In this paper the accuracy of five of the best solutions currently available is tested by comparing them with the exact modal solution. This comparison is accomplished by placing the modal solution in a more efficient form for numerical evaluation. From a study of four ray trajectories on cylinders of radius 1.5171 and four wavelengths it is concluded that two complementing solutions due to Boersma and Lee and the author have best overall accuracy. The former solution is most accurate near the source and in the paraxial region while the Latter is best far from the source and off axis. The worst case errors observed for the test trajectories on the four wavelength cylinder were approximately 1 dB in magnitude and3degin phase for the Boersma-Lee solution and 0.5 dB and4deg, respectively, for the author's solution. Generally the errors arc considerably less than these values.     

双指数源激励下垂直电偶极子产生的极低频近场

针对雷电过程在地面产生的近区极低频电磁脉冲,推导出了双指数模型激励下垂直电偶极子产生的极低频电磁场的瞬态近似表达式.该方案基于Sommerfeld积分在准静态近似下求解,从频域出发,利用单位脉冲响应的近似结果与双指数模型激励源卷积计算的方法,通过傅里叶逆变换,得到了双指数源激励下的瞬态解析表达式,其可用于模拟雷电信号产...     

FDTD模拟SLF\ELF水平电偶极子在非均匀地-电离层波导中的场

在SLF/ELF频段,已有的解析算法对于研究其在非均匀电离层模型下的电磁特性有很大的局限性。采用三维球坐标时域有限差分方法(FDTD)计算了非均匀电离层模型下(考虑电离层白天和黑夜不对称),水平电偶极子产生的SLF/ELF波在球形地-电离层腔体中的传播特性。计算了电场分量和磁场分量沿地面随传播距离的变化,以及随方位角的变化。和均匀电离层模型对比,非均匀电离层模型的计算结果更具有实际意义。     

Asymptotic analysis and numerical evaluation of short pulseradiation from a point dipole in a grounded dielectric layer

In a companion paper (see ibid., p.747-54, Jun 1993) spectral options for the synthesis of the electromagnetic fields radiated into the exterior by a pulsed electric current element inside a grounded dielectric layer are presented. The exact spectral integrals, which implement these spectral alternatives, are reduced here by asymptotic methods that extract explicit approximate forms for wavefront contributions, time-domain (TD) leaky mode contributions with space-time dependent wavenumbers and frequencies, and self-consistent hybrid combinations of both. The resulting hybrid wavefront-TD-leaky-mode algorithm is explained in physical terms and tested numerically. For both TE and TM contributions, it is found that in their domain of validity, the TD leaky modes excited within the frequency spectrum of the source pulse synthesize with remarkable accuracy the highly resolved pulse train obtained by direct tracking of multiple reflected wavefronts. Of special interest is the anomalous behavior of the TM-TD leaky modes when their angular spectra are near the Brewster angle for the air-dielectric interface. The correspondingly anomalous asymptotics is explained in detail     

源嵌入负折射率传输线介质板的透镜成像研究

分析了板内无数个电流源所激励起的平面电压波与负折射率传输线媒质平板透镜的相互作用,导出了平板透镜内外的电压分布,并着重讨论了倏逝波和传播波在z方向的波矢。微波电路仿真结果表明：由于板内倏逝场的增强,在透镜两个界面附近存在很高的电压波幅度。该结果证实了源点的倏逝波幅度在像点被精确地重构,从而取得亚波长成像。最后给出了板内单个电流源产生的电压解。