A caustic corrected UTD solution for the fields radiated by asource on a flat plate with a curved edge

Corrections to the uniform geometrical theory of diffraction (UTD) that account for the caustics caused by the coalescence of the diffraction points on a curved edge are derived. This creates a new curvature dependent diffraction coefficient that has not been previously accounted for in the UTD. The far-zone radiation by a short monopole mounted on an elliptic disk is analyzed using this caustic corrected UTD solution. Theoretical results are verified in the principal plane by comparison with a method of moments solution. The resulting solution for the radiated field is accurate and provides useful insight into the scattering phenomena. This insight is necessary in order to obtain more general solutions     

Contribution of a single face to the wedge diffracted field

In certain wedge diffraction problems, it is advantageous to know the part of the diffracted field created by the currents induced on a single face of the wedge. The rigorous solution to the corresponding canonical problem is derived. This solution indicates which part of the uniform theory of diffraction (UTD) solution for the wedge-diffracted field should be taken to describe its single-face component.     

A method of evaluating the near diffracted field

A simple expression for the diffracted field by a slit or a flanged parallel-plate waveguide is derived from which we can readily evaluate the near field by applying the fast Fourier transform. Some numerical results are presented for the diffracted wave of an isotropic cylindrical wave by an infinitely long slit in a thin conducting screen.     

An extension to GTD for an edge on a curved perfectly conducting surface

The construction of a high-frequency solution for the generation of edge-diffracted space rays and edge-excited surface rays by an electromagnetic wave normally incident on the edge of a curved perfectly conducting surface surrounded by an homogeneous medium is considered. The solution is a collection of the results of second degree canonical problems considered by Idemen et al. which will be cast into forms appropriate to numerical applications.     

Statistical properties of the field diffracted by an aperture with partially coherent illumination

The statistical properties of the electromagnetic field diffracted by a plane aperture illuminated by a fluctuating field have been studied in the Fresnel zone on the basis of the theory of partial coherence. The average power distribution and the amplitude and phase of the degree of coherence have been computed for several coherence lengths of the illuminating field ranging from 1/4 to 5 times the dimension of the aperture and for two geometries of the observation points. The obtained results indicate the limits of validity of the often assumed hypothesis of spatial stationarity and of the real Gaussian approximation for the degree of coherence of the diffracted field. It turns out also that the optimum position of a receiving phase-sensitive system placed in the field diffracted by an aperture may not be the focus of the aperture, since there the concentration of average power density is accompanied by a poor coherence of the field.     

Diffraction of a TM whispering gallery mode by the edge of a nonperfectly conducting spherically curved sheet

Electromagnetic scattering is a function of the scatterer's material properties as well as its geometry. Therefore, it is necessary to examine the effect of the physical properties of a body on diffraction phenomena besides the geometrical properties. The aim here is to give a rigorous asymptotic solution for the diffraction of high-frequency electromagnetic fields by an edge on a spherically curved sheet having a particular impedance property. The solution is interpreted with the terminology of the geometrical theory of diffraction (GTD).     

矢量空心光束的半屏衍射

利用矢量瑞利——索墨菲衍射积分公式推出了空心光束半屏衍射场中衍射场的解析表达式,并数值模拟了衍射场的光强空间分布及强度奇点的相关属性。结果表明：衍射场光强已不再是空心分布,发生了很大的改变;随着衍射传输距离的增大,衍射场光强的空间分布退化为类TEM02模场分布;随着传输距离的增大,衍射场观察区域内光强奇点出现湮灭等。     

平面波经方环衍射后的光束质量评价

在对平面波经方环衍射后远场光强分布分析的基础上,对其光束质量作了详细研究。数值计算结果的物理分析表明,可用“桶中功率”曲线、β和 η参数评价这类环状光束的光束质量。同时也指出了这些方法的不足。     

部分相干光束经刀边衍射产生的光谱变化

从部分相干光束的传输定律出发,得到了部分相干光束刀边衍射时的远场光谱的表达式．根据该表达式对衍射场中的光谱进行了理论研究。研究的结果表明：衍射场中的光谱将随着观察点位置而改变,并且对于固定观察点,其光谱将随着相对空间相干度以及光束透过率的变化而变化。     

The interaction of relativistic electron beam with the electromagnetic field in the neighbourhood of a caustic region

We present the theory of self-consistent interaction of crooked relativistic electron beam within and near the e.m. field caustic zones of jumping ball and whispering gallery types being formed in open resonators of elliptical cylindrical symmetry. On the basis of numerical analysis of nonlinear system of equations by applying a large-particles method, the principal possibility to design the multiwave synchro-Cherenkov amplifiers and generators is shown.     

非傍轴高斯光束通过小孔光阑衍射的轴上光强

基于瑞利衍射积分,不使用通常的近似Rλ(λ为波长),推导出非傍轴高斯光束通过小孔光阑衍射的轴上光强的精确解析表达式。并对传统的光强定义和光强的精确表述进行了比较研究。结果表明,两种定义之间的差异与f参数,截断参数δ和传输距离z有关。     

Diffraction corrections to the cylindrical wave radiated by a linear array feed of a cylindrical reflector antenna

A phase-steered linear array feed for a parabolic cylindrical reflector antenna is considered. The nearly cylindrical wave radiated from this line feed in the Fresnel zone is expressed in terms of the isolated-element pattern. The correction to this wave due to diffraction from the endpoints of the line feed and from the grating formed by the array elements is also derived.     

The perfectly conducting wire grating: Computation of the diffracted field from Maxwell's equations and Hamilton's canonical system

A theoretical and numerical study of the perfectly conducting wire grating is presented. For both fundamental cases of polarization, we solve the Helmholtz equation rigorously without any physical simplifying assumption. The only approximations are due to the use of numerical techniques in the integration of a differential system. The wire cross section is to a large extent arbitrary. The interest of Hamilton's canonical equations in the numerical treatment of certain practical problems is shown. No doubt, certain ideas contained herein could be adapted for solving many other problems in electromagnetic theory.     

Quantum corrections to the conductivity of a two-dimensional system with antidots

The quantum corrections to the conductivity of a two-dimensional electron system with antidots in the limit of a small antidot density are investigated. The corrections to the conductivity and magnetoconductivity due to the presence of antidots in a magnetic field perpendicular to the plane of the system are considered. It is assumed that the mean free path l of electrons on the impurities is far smaller than the antidot radius. Fiz. Tekh. Poluprovodn. 32, 1461–1466 (December 1998)     

Closer to the edge

The next generation of distributed systems will be loosely-coupled systems that: support incremental and independent development, and are tolerant of interface changes; can systematically deal with impedance mismatches; and work well in dynamically changing realtime situations; and can scale in complexity while delivering the required real-time performance. Popular architectural styles, including data flow architecture, event driven architecture and service-oriented architecture, can be regarded as special cases, by the appropriate assignment of roles and choice of quality of service in the interfaces between components. Data-oriented application architecture coupled with an appropriate standards based messaging software bus such as DDS can cut down the complexity of the integration problem from O(N*N) to O(N), while preserving loose-coupling and ensuring scalability. Having readily available middleware infrastructure bridges for popular application platform components can greatly boost productivity and the pace of integration     

Fields of a curved plasma layer excited by a slot

An analysis of the fields of a plasma coated conducting cylinder of infinite extent, excited by an infinite axial slot, is presented for large radius cylinders. The saddle point evaluation of the radiation fields is discussed for uniform low-loss plasma layers of arbitrary thickness and index of refraction. Patterns are presented and compared with the flat layer case, and the effect of the curvature on the pattern is discussed. The residue series evaluation is considered and a method of determining the poles is discussed. The locus of the first pole for thin lossless dielectric layers is presented and the transition from leaky waves to surface waves is discussed as a function of the dielectric constant and radius of curvature.     

Common-mode current due to a trace near a PCB edge and its suppression by a guard band

The common-mode (CM) current due to a trace near a printed circuit board (PCB) edge, and its suppression by a guard band have been studied experimentally and with finite-difference time-domain (FDTD) modeling. As the guard band, copper tape is connected along the entire edge of the ground plane. First, a PCB electromagnetic interference (EMI) coupling path that results from the nonzero impedance of the PCB ground plane is discussed. As the trace is moved closer to the PCB edge, the CM current increases. Then, the effect of the guard band on the CM current is detailed. A guard band parallel to and near a trace is most effective in suppressing the CM current. The cross-sectional magnetic field distribution at center of the PCB with and without the guard band is also calculated with FDTD modeling. The guard band decreases the magnetic field distributed on the reverse side of a PCB. These results indicate the guard band is effective in suppressing CM current. Finally, an empirical formula to quantify the relationship between the position of a trace and CM current for the case with a guard band is proposed. Calculated results using the empirical formula and FDTD modeling are in good agreement, which indicates this empirical formula should be useful for developing EMI design guidelines.     

A concise analytical approach for predicting the voltage and edge peak field profiles of the planar junction with a single floating field limiting ring

A concise analytical approach for predicting the voltage and edge peak field profiles of the planar junction with a single floating field limiting ring is proposed in this paper. From this analysis, the effects of the background doping concentration, junction depth and reversed voltage on the voltage and edge peak field profiles are analysed. The optimal distance between the main junction and the ring junction is also obtained. The analytical results are in excellent agreement with that of the two-dimensional semiconductor device simulator DESSIS-ISE, showing the validity of the approach presented.