爬行波电流传播常数及幅度的计算

本文提出了一种计算金属圆柱表面爬行波电流传播常数和幅度的新方法。该方法在获得金属柱表面爬行波电流的精确数值解后，应用Ｐｒｏｎｙ方法得了金属表面爬行波电流各个模的传播常数和幅度，避开了传统方法解时冗长、繁锁的数学推导过程。经比较，本文方法的计算结果比几何绕射理论的计算结果更为精确。     

三维机翼前缘影区爬行波RCS研究

分析了三维机翼前缘影区的爬行波散射机理,建立了前缘影区爬行波的雷达散射截面(RCS)计算模型.根据光滑凸曲面的一致性绕射理论(UTD)给出爬行波的后向散射远区电磁场计算公式,按RCS定义计算爬行波散射贡献.采用微分几何原理分析任意凸曲面上的爬行波短程线特性,根据爬行波在光滑凸曲面上的短程线测地曲率为零的条件,给出一种三维机翼表面短程线计算方法.对三维机翼前缘爬行波进行计算和测试,并计算分析不同机翼参数对前缘影区爬行波的影响.计算结果和测试结果吻合良好,表明该方法计算爬行波RCS快捷有效,可应用于工程分析.     

光滑曲面上测地线射线寻迹算法及爬行波计算

提出了一种光滑凸曲面上的一致性几何绕射理论(UTD)爬行波射线寻迹算法,该算法结合泰勒级数,并根据测地线的相关性质,使用计算几何方法对暗区爬行波射线进行寻迹;在参数曲面片上根据测地线性质求解爬行波轨迹点,并对爬行波在任意一点处的测地曲率进行计算,结果准确度高。最后使用该算法结合UTD方法计算二维圆柱的散射场,得到的结果与级数解吻合,验证了本文算法的有效性,扩展了UTD方法在实际工程中的应用。     

谐振区目标散射特性与曲面绕射机理的研究

针对目标在谐振区的散射模型，提出了将高频方法应用于谐振区的两种改进办法，用以解决高频方法在谐振区精确度有所下降的问题.在谐振区，随着频率和目标电尺寸的降低，对于表达式中的高频级数解，需要更多的求和项才能使级数得以收敛，除此之外还考察了高阶爬行波对散射场的影响.在此基础上，为了分析谐振区的散射特性与散射机理，将混合几何光学-物理光学算法与一致性几何绕射理论相结合，同时推导了爬行波随爬行距离等参数衰减的表达式，并且通过计算金属球和二维圆柱的散射场，总结出目标在谐振区的散射特性.     

圆柱体上爬行波场分析及电磁兼容性设计应用

航空器上天线间辐射干扰问题的解决是系统正常通讯的保证。文章针对各种航空器的典型结构模型-圆柱体进行研究，应用几何绕射理论分析了圆柱体上爬行波场的分布规律，包括固定收发天线位置，频率变化时爬行波场分布规律和固定天线工作频率改变收发天线相地位置时场的分布规律，所得结论为解决航空器上天线系统空间布局的电磁兼容问题提供了设计依据，也为定量地预测天线间隔离度提供了有效手段。     

Mg：Fe：LinbO_3晶体光折变增强效应的研究

在铌酸锂晶体中掺ＭｇＯ和Ｆｅ２Ｏ３，生长出Ｍｇ：Ｆｅ：ＬｉＮｂＯ３晶体．由于薄晶片的光爬行效应，晶体的二波耦合指数增益系数高达８０ｃｍ－１，且角度响应范围加宽，响应速度和抗光散射能力都比Ｆｅ：ＬｉＮｂＯ３有较大改善．以Ｍｇ：Ｆｅ：ＬｉＮｂＯ３晶体作光放大器，实现了一次迭代全息关联存储．     

源在曲面上的NURBS-UTD方法的爬行波射线寻迹算法研究

辐射源位于凸曲面上的一致性几何绕射理论(UTD)在分析设计电大尺寸平台上天线的应用广泛,本文给出了一种源点位于任意光滑凸曲面上的UTD爬行波射线寻迹算法,使用数值的微分几何方法对暗区爬行波射线进行寻迹.对目标模型引入非均匀有理B样条(NURBS)曲面进行建模,这使得UTD方法可以应用于以往板、柱、锥模型以外的任意光滑曲面模型.本文算法可应用于任意曲面上,数值结果表明了本文算法的有效性及工程适用性.     

介质覆盖体上过渡区和焦散区的场分析

本文应用几何绕射理论对介质覆盖体上过渡区和焦散区的场进行了详细地分析，在对过滤区的分析中，通过对留数级数解的修正，实现了场地直接计算，而对于由爬行波产生的焦散区则通过扩展等效电磁流的概念来加以分析。计算结果均与经典解进行了比较以证实本方法的有效性。     

解决电磁散射问题的现代高频技术

电大尺寸散射体的高频散射高效算法问题是一个重要而具有挑战性的问题.本文首先对解决电磁散射问题的现代高频方法的研究进展进行了综述.其次，对高频散射场的高振荡特性，提出了数值最速下降路径法来计算高频散射场.最后，综合讨论了高频驻相点贡献凯勒锥以及爬行波场.     

基于阈值决策的子波域去噪方法

通过对信号多尺度边缘滤波和Ｄｏｎｏｈｏ阈值决策子波域滤波方法（Ｃ－Ｄ方法）进行研究，首先给出了Ｃ－Ｄ阈值选取证明，推导了理论阈值，接着将Ｃ－Ｄ推广到非正交子波基，使其不仅适用于正交多分辨分解，亦适用于离散子波变换，本文对一维和二维信号的多种子波滤波算法进行了仿真计算，全面分析了Ｃ－Ｄ算法的性能。     

Creeping wave propagation constants and modal impedance for a dielectric coated cylinder

The electromagnetic characteristics associated with the creeping waves supported by a dielectric coated cylinder are investigated. The propagation constants and wave impedances of the creeping waves are obtained numerically. Higher order modes which are significant for a thick coating are also investigated. The propagation constants and creeping wave modal impedance are compared with those obtained for a planar dielectric slab backed by a ground plane. It is found that, contrary to the planar configuration, no cutoff frequencies exist for the creeping waves associated with the coated cylinder. In fact, the coated cylinder supports an infinite number of modes. However, depending upon the thickness of the coating, only a few Elliott type creeping wave modes with low attenuation can exist. Furthermore, for each of the Elliott type creeping waves, there is a critical radius for the cylinder below which the Elliott type creeping wave cannot exist. The results are also compared with an impedance boundary cylinder, where the impedance is chosen to be purely imaginary.     

Electromagnetic resonances of immersed dielectric spheres

The complex natural resonances (CNR) for lossless dielectric spheres in a lossless dielectric medium are investigated. Significant differences between the external and internal resonances are presented. The external resonances are related to the external creeping waves and the internal resonances to the internally reflected waves. The internal resonances are more important in practice because of their smaller damping factors. A simple physical interpretation for predicting the resonance behavior of a general dielectric sphere is obtained     

Near axial backscattering from finite cones

The near-axial backscattering from a finite cone is studied using the equivalent current concept based on the uniform geometrical theory of diffraction (UTD). The creeping waves associated with the conical surface are also incorporated into the equivalent current technique. The contributions from the creeping waves are significant for the oblique-incidence case. There is evidence to speculate that the poorer agreement between the previously calculated results and the measured data for the vertically polarized backscattering is probably a result of the omission of the creeping wave contribution     

An effect of excitation of a transverse magnetic creeping wave when a transverse electric wave crosses the line of the coincidence of propagation constants

Transverse electromagnetic electric (TE) and transverse magnetic (TM) creeping waves on a surface with an anisotropic impedance boundary condition are considered. An asymptotic theory is developed for creeping waves. The theory is valid near the line where the attenuation parameters of two different types of waves coincide and, therefore, standard asymptotics are inapplicable. Asymptotic formulas describing physical effects that occur when a creeping wave propagates across the degeneracy line are derived. It is found that, behind the degeneracy line, a propagating TE wave excites a TM wave with a small amplitude (of order O(k ^−1/6)) and a propagating TM wave excites a TE wave.     

Transient currents on a cylinder illuminated by an impulsive plane wave

An analytical and numerical study of the transient current density induced on a perfectly conducting circular cylinder has been carried out. Both TE and TM incident plane waves with impulsive time dependence are considered. Complete closed form expressions for the TE and TM current density at all points on the cylinder and for all time values are obtained by a functional interpolation of both large and small time asymptotic solutions. The complete expressions should he useful in future transient radar scattering problems for approximating the transient current behavior on portions of a complex scatterer. The numerical results are presented in the form of "snapshots" of the current density at specific instants of time. The results are interpreted in terms of specular reflection and creeping waves. The creeping wave pulses are seen to be a continuation of pulses generated on the illuminated surface; their propagation into the shadow region is a highly dispersive phenomenon. The natural mode spectrum is seen to have both discrete and continuous components with the response at very large times determined by the latter.     

Theory of absorbers in scattering

The effect of absorbers on scattering from complex shapes is considered, wherein, unlike previous work on the subject, the diffracted field is taken into account. For a general class of scattering bodies two new theorems are introduced which give conditions under which the back-scattered field for incident radiation is identically zero. High-frequency scattering from any smooth convex body is examined. The conditions given in the theorems are then used to determine their effect on the creeping waves. It is shown that the creeping waves suffer much greater attenuation than they would if the body were a perfectly conducting surface. The particular case for nose-on back-scattering from a body of revolution is considered, for which case the creeping wave contribution to the back-scattered field is identically zero due to phase cancellation. It is then shown that absorbers with highly refractive lossy characteristics will reduce the back-scattered cross section for smooth convex bodies in the resonance region.     

Ondes rampantes sur un objet convexe Décrit par une condition D’impédance anisotrope

We study the propagation of creeping waves on a convex object satisfying an anisotropic impedance boundary condition. We obtain, as in the case of an Isotropie impedance, two independant creeping wave modes. However, the presence of a non zero extra-diagonal term in the impedance matrice is responsible for new physical phenomena : both modes have non zero components of electric and magnetic fields along the creeping ray binormal; moreover, the propagation constants are modified by this extradiagonal term ; finally, the equation giving the amplitude of the creeping wave is modified by new terms, one algebric and one exponential. These effects only appear when the extradiagonal term is different from zero. When this term is equal to zero, the results are similar to the Isotropie impedance case.     

Creeping wave modes for a dielectric coated cylinder

A new system of poles for the Green's function for a dielectric-coated cylinder has been found. In general, these poles correspond to creeping waves, which are strongly attenuated except for very thick coatings. For radii below a critical value, one of the new poles replaces one of those previously described in the literature and gives rise to a creeping wave of Elliott type with low attenuation     

Element pattern for circular arrays of waveguide-fed axial slits on large conducting cylinders

Analytical and numerical results are presented for the array element pattern of axial slits in conducting cylinders. The slits are fed by parallel-plate guides in the TEM mode and are matched to free space. Both harmonic series and integral representation for the far-field patterns are obtained and numerically evaluated as a function ofkr_{0}and spacing. The integral representation is treated asymptotically for large values ofkr_{0}. The element patterns exhibit two characteristic features: a dip off broadside and a ripple in the main beam near broadside, the level of both beingkr_{0}dependent. While the harmonic series offers no basis for an explanation of these effects, the asymptotics clearly demonstrates that the pattern can be decomposed into two parts: 1) a space wave contribution which can be directly obtained by substituting the circular array "admittance crater" into the appropriate planar array formulas and exhibits a dip analogous to a grating lobe effect; 2) a set of creeping waves which, unlike the more common type, contribute significantly in the forward region and, by interfering with the space wave, cause the ripple near broadside. These creeping waves are the fast (usuallyn = -1) space harmonics (grating lobes) of the fundamental, slightly slow set, and their presence does not seem to have been recognized in the literature.     

Degeneration of Electromagnetic Creeping Waves in a Vicinity of Critical Values of Anisotropic Impedance

Electromagnetic creeping waves on a 3-dimensional surface with an anisotropic impedance boundary condition are considered. The influence of the impedance is examined. The standard asymptotic formula for the creeping waves contains the factor $1/(tau-q^{2})$ where $tau$ is the attenuation parameter and $q$ is the Fock parameter which depends on the impedance matrix. Analysis of the equation for the attenuation parameter which describes its dependence on $q$ shows that there exist such critical values of $q$ when the factor $1/(tau-q^{2})$ diverges and the usual asymptotic formula gives infinite result. The equation for the critical values of the parameter $q$ is derived and the 4 first critical values are found numerically. The new local asymptotics valid in domain of the size $k^{-2/9}$ (where $k$ is the wave number) is derived in the supposition that the divergence takes place on a curve crossed by creeping waves. This new asymptotic decomposition is carried out by powers of the small parameter $k^{-1/9}$. The effect of creeping wave passing through the line where the usual asymptotics diverges is examined.