Fields of electric dipole on radially inhomogeneous ground surface

An integral-equation method is employed to calculate the fields for low-angle radiation over a plane boundary with an exponentially varying surface impedance. It is shown that the effective dipole moment of the source is increased by a complex factor which depends on both the taper and the extent of the inhomogeneous region.     

Far-field transforms for finite element frequency-domain solutions

Methods of calculating far-field quantities from a two-dimensional finite element/absorbing boundary solution of unbounded RF electromagnetic fields are presented. Three different methods are developed and compared in terms of accuracy, efficiency, and capabilities. The three methods are: harmonic expansion, Green's theorem integral, and volume sources radiation integral     

Extension of on-surface radiation condition theory to scattering bytwo-dimensional homogeneous dielectric objects

A recent analytical formulation by G.A. Kriegsmann et al. (see ibid., vol.AP-35, p.153-61, Feb. 1987) of electromagnetic wave scattering by perfectly conducting two-dimensional objects using the on-surface radiation boundary condition approach is extended to the case of two-dimensional homogeneous convex dielectric objects. It is shown that a substantial simplification in the analysis can be obtained by applying the outgoing radiation boundary condition on the surface of the object. The analysis procedure decouples the fields in the two regions to yield explicitly a differential equation relationship between the external incident field excitation and the corresponding field distribution in the interior of the dielectric object. The interior fields can be obtained by solving the differential equation using either an analytical approach or a suitable numerical method. Two-dimensional scattering examples along with validations are reported, showing the near-surface field distributions for a homogeneous circular dielectric cylinder and an elliptic dielectric cylinder, with with transverse magnetic plane-wave excitation     

腔基微带天线的矢量有限元--边界积分方法分析

该文将矢量有限元——边界积分(Edge-Based FE-BI)混合方法用于腔基微带贴片线的辐射特性分析。分别计算了在无阻抗负载和加有阻抗负载两种情况下的输入阻抗，以此验证了该混合方法的正确性；然后计算了贴片天线表面缝隙部分的场分布，验证微带天线分析模型——传输线模型的合理性；最后计算了E面、H面方向图以及相应的交叉极化方向图。     

Artificially soft and hard surfaces in electromagnetics

A transversely corrugated surface as used in corrugated horn antennas represents a soft boundary. A hard boundary is made by using longitudinal corrugations filled with dielectric material. The concept of soft and hard surfaces is treated in detail, considering different geometries. It is shown that both the hard and soft boundaries have the advantage of a polarization-independent reflection coefficient for geometrical optics ray fields, so that a circularly polarized wave is circularly polarized in the same sense after reflection. The hard boundary can be used to obtain strong radiation fields along a surface for any polarization, whereas the soft boundary makes the fields radiated along the surface zero     

截断各向异性介质的修正NPML吸收边界条件

基于各向异性介质中的时域有限差分（Finite-Difference Time-Domain,FDTD）方法及近似完全匹配层（Nearly Perfect Match Layer,NPML）原理,提出一种截断各向异性介质的修正的NPML吸收边界条件.通过对Maxwell旋度方程中的空间偏导数进行坐标拉伸并结合空间插值方法,推导出易于在FDTD方法中实现的吸收边界公式.计算了电偶极子辐射场的反射误差,验证了这种吸收边界截断二维各向异性介质的有效性.三维算例中数值模拟了时谐场的相位分布,以及不同网格NPML吸收层随时间变化的反射误差.数值结果表明NPML吸收边界能有效吸收各向异性介质中的电磁波.     

Asymptotic boundary conditions for strip-loaded scatterers appliedto circular dielectric cylinders under oblique incidence

This paper describes an asymptotic boundary condition which can be used to model grids of metal strips which are located in free space, inside a material or at a material interface. The boundary condition is asymptotic in the sense that it becomes more accurate the smaller the period of the grid is in terms of the wavelength. The boundary condition is very simple to implement in existing computer programs for calculation of scattering or radiation based on any numerical technique. The method replaces the use of complicated Floquet-mode expansion of the fields scattered by the grid. As an example, we show how to apply the method to calculate the plane-wave scattering from two circular dielectric cylinders under oblique incidence, one loaded with circumferential strips and the other with longitudinal strips. In both cases, analytic series solutions are derived. The results are verified with measurements on cylinders with finite strip periods and widths     

固液混合火箭发动机尾焰的红外特性研究

针对固液混合火箭发动机中Al2O3颗粒运动的影响,对喷管的内流场和外流场进行了一体化数值仿真,得到了温度、压力、组分浓度以及粒子浓度等参数的分布。利用以最新的分子光谱数据库HITRAN和HITEMP为基础编写的逐线积分法计算了气体光谱吸收系数,采用米氏散射模型计算了固体粒子的辐射特性参数。利用基于有限体积法离散辐射传输方程的模型计算出了尾焰的红外辐射亮度。通过进一步求解,得到了特定波段的光谱辐射强度。在8—14岬波段,利用红外热像仪进行了试验,并将试验结果与数值计算结果进行了比较。结果表明,该计算模型和方法能较好地模拟固液混合火箭发动机尾焰的红外辐射特性。     

Excitation of layered media having rough interfaces by line sources

A method for determining the radiation characteristics of a line source embedded in a layered medium having rough interfaces is described. This technique utilizes the plane wave spectral decomposition of the relevant fields in the framework of the extended boundary condition method. It is also shown that the equations derived for the general case reduce considerably when the interfaces are periodically rough. Extensions of the problem solved here have been briefly mentioned, and some numerical examples have been provided.     

Coupling Between Guided Surface Waves, Lateral Waves, and the Radiation Fields by Rough Surfaces--Full-Wave Solutions

In this paper explicit expressions are presented for the guided surface waves and lateral waves that are excited when radiation fields are incident upon rough surfaces. Similarly, expressions are presented for the radiation fields scattered by rough surfaces that are excited by surface waves and lateral waves. In addition, coupling between the surface waves and the lateral waves due to surface irregularities is considered in detail. The solutions, which are based on a full-wave approach to the problem, are subject to the exact boundary conditions at the irregular interface. These are shown to be consistent with the reciprocity relationship in electromagnetic theory. The validity of the approximate impedance boundary condition is examined and consideration is given to excitation at the grazing incidence, the Brewster angle, and to waves incident at the critical angle for total internal reflection. Optimum conditions are determined for coupling between the radiation fields, the surface waves, and the Iateral waves incident upon irregular boundaries. Thus this work is applicable to problems of radio wave propagation near an irregular interface between two media and excitation of guided waves by irregular dielectric structures.     

Boundary conditions for the finite difference beam propagationmethod based on plane wave solutions of the Fresnel equation

Each particular implementation of the beam propagation method (BPM) requires a special procedure allowing for radiation to leave the computational window. We propose a new approach to constructing the finite difference schemes of the BPM at the boundary of the computational window. These schemes are independent of the computed fields and allow for a similar treatment of both interior and boundary points. The new approach can be further improved by correcting the field values at the boundary points according to Hadley's method. The algorithm is easy to implement for both two- and three-dimensional structures. The new method considerably reduces computation times because the propagation matrices remain constant in longitudinally invariant sections, thus avoiding repeated LU-decompositions. The basic idea-establishing the finite difference scheme such that locally exact, approximate, or plausible solutions are recovered-may be of interest for other efforts to solve partial differential equations by the finite difference method     

轨控推进器尾焰对太阳辐射吸收的研究

为掌握轨控推进器尾焰的吸收特性,研究了尾焰对太阳红外辐射的吸收问题.在贴体坐标系下,运用有限体积法,建立了尾焰对太阳红外辐射的吸收模型.经过求解,获得受到尾焰吸收后、在尾焰边界处的太阳光谱辐射亮度.比较吸收前和吸收后太阳的光谱辐射亮度,发现,当喷口距离等于0.483 m时,在波数1700 cm-1、2155 cm-1、...     

Full-wave analysis and wide-band design of probe-fed multilayered cylindrical-rectangular microstrip antennas

The input impedance and radiation pattern of the probe-fed multilayered cylindrical-rectangular microstrip antennas (PMCMSA) are analyzed by using a novel approach which combines the conformal finite-difference time-domain (FDTD) and Gedney's unsplit version of the perfectly matched layer absorbing boundary condition method and the Green's functions in cylindrically stratified media. The near fields of such antennas and the current distributions on the patches are obtained by the conformal FDTD method numerically and then the modified spectral-domain Green's functions in arbitrary cylindrically stratified media are used to determine the radiation pattern. The effect of the small radius of the probe on the performance of antennas is investigated through the thin-wire algorithm in cylindrical coordinates. A simple design scheme of the probe-fed cylindrically stacked antennas is also proposed for increasing the impedance bandwidth.     

Full wave and physical optics solutions for scattered radiation fields by rough surfaces-energy and reciprocity relationships

Full wave and physical optics solutions for the scattered radiation fields from rough surfaces are compared. The full wave solutions involve complete expansions of the fields and exact boundary conditions. The solutions for the radiation fields axe provided in a form that can be readily compared with earlier solutions to the problem, and they can be applied directly to engineering problems without the need to carry out any of the analytic procedures encountered in the derivations. The surface impedance concept, reciprocity, and energy conservation relationships are considered in detail, and special consideration is given to grazing incidence and excitation at the Brewster angle. This work on irregular ground effects on radio wave propagation is relevant to problems of communication, navigation, and active remote sensing.     

Sphere-TEM mode in rectangular top horn offset coaxial transmissionline

We analyze electromagnetic characteristics of the sphere-TEM mode (S-TEM) in a rectangular top horn offset coaxial transmission line (RTHOCT) by spherical wave and independent mode propagation theory. In our analysis, the boundary integral equation technique and multi-local expansion method (MILEM) are applied. The computational practice shows that MILEM can accelerate the convergence of the computational procedure to the EM problems with complex boundaries and multi-singular points. The error of the normalized electric potential along the boundary of RTHOCT is less than 10^-3 in most parts and 10^-2 in the other parts. The numerical results of the electric fields demonstrate a volume with an uniform electric field in RTHOCT. The volume is changeable through careful optimum design. The existence of the volume is a basic factor in using RTHOCT to manufacture a GTEM cell     

Three-dimensional analysis of a through hole with radiationcharacteristics by the spatial network method

Through holes generate complicated distributions of electromagnetic fields owing to their three-dimensional structures. Rigorous vectorial analyses must be performed for three-dimensional fields by using all field components, boundary conditions, and properties of the medium. The spatial network method, which has many features for analysis of three-dimensional electromagnetic fields in the time domain, was applied to this analysis. The variation of Poynting vector distributions near the through hole is simulated in the time domain. From the distribution of the electric field on the top plane of the through hole containing the connected stripline and the land, the far-field patterns are computed by the Fourier transform. Fundamental characteristics of the radiation from the through hole are thereby obtained     

Time domain analysis of patch antennas in a magnetized plasma bythe spatial network method

The near field of a patch antenna in a magnetized plasma is simulated by use of the spatial network method, which is a three-dimensional time domain simulation method. Two fundamental cases are examined in the radiated field: where the direction of the constant magnetic field is perpendicular to the patch plane, and where it is parallel. Results show that radiation characteristics of patch antennas in a magnetized plasma are different from those in free space. It was also confirmed that the Faraday effect is shown in the near field when a perpendicular constant magnetic field is applied to the antenna. In this analysis, the free boundary condition is approximated by terminating the volume with the free space characteristic impedance. A stricter model is necessary, if a reflectionless boundary is to be realized     

Least Squares Boundary Residual Method for the Analysis of Step Discontinuities in Open Chiral Waveguides

We analyse the reflection, transmission and radiation characteristics of a step discontinuity in a grounded chiral slab and we show that the step radiation can be enhanced due to the effect of the chirality. The analysis is performed using a mode matching technique. The fields are expressed in terms of the discrete modes and the continuous spectrum using two subsets of hybrid radiation modes: incident transverse electric (ITE) and incident transverse magnetic (ITM) modes. The scattering matrix of the step is determined by minimizing the boundary residual error in the sense of the least squares. The influence of chirality on the characterization of the step is demonstrated and we show that control of the radiation pattern is achieved, including angle and width of the radiation beam.     

A note on the radiation boundary conditions for the Helmholtzequation

The radiation boundary conditions in two dimensions are derived in the body-fitted coordinate system using the method of successive approximations for the wave envelope function. Results are valid for a convex scatterer with continuous radius of curvature on the surface of the scatterer. In the special case when the computational boundary is circular, the boundary operators derived are identical to the Bayliss operators. The on-surface radiation condition is examined. It is shown that, for a large conducting circular cylinder, a boundary operator of infinite order should be used due to the breakdown of the asymptotic expansions of the boundary operators on the surface of the scatterer. The leading order result based on the boundary operator of infinite order applied on the surface of the cylinder is the same as the result obtained by the method of physical optics     

A hybrid FEM/MOM technique for electromagnetic scattering andradiation from dielectric objects with attached wires

A hybrid formulation is presented, which combines the method of moments (MOM) with the edge-based vector finite element method (FEM) to solve electromagnetic radiation problems from structures consisting of an inhomogeneous dielectric body of arbitrary shape attached to one or more perfectly conducting bodies. While either method alone fails to model these structures efficiently, a combination of both finite element and moment methods provides an excellent way to solve these problems. The FEM is employed to handle the interior domain of inhomogeneous dielectric bodies and the method of moments is used to develop surface integrals that relate the field quantities on boundary surfaces with the equivalent surface currents. These integral equations are then coupled to the finite element equations through the continuity of the tangential magnetic fields across the hybrid boundaries