分层伦伯透镜天线的辐射性能计算

介绍了伦伯透镜及伦伯透镜天线的特点，用经典电磁理论模式展开法计算平面波入射分层伦伯透镜时的散射场，然后利用此结论和互易定理计算喇叭天线作为馈源时伦伯透镜天线的辐射场。     

A multi-beam planar lens antenna for UAV relay datalink

龙伯透镜天线表面放置多个馈源即可在同一频段或跨频段同时产生多个扫描波束跟踪多个目标,针对这一特点,设计了适用于C频段无人机中继数据链的紧凑多波束平板透镜天线。采用矢量球面波函数展开法结合差分进化算法优化设计透镜天线,仿真分析了单个Vivaldi天线照射3层直径160 mm平板透镜天线,天线增益优于传统均匀分层的透镜天线。同时,采用16个Vivaldi天线组成半圆环阵照射平板透镜天线,通过扫描波束的馈电切换,实现宽角范围的多波束覆盖。仿真结果表明:平板透镜天线在宽频带(5.5~9.0 GHz)内具有良好的多波束辐射特性。     

双层介质周期漏波天线的辐射特性分析

利用互易性和谱域矩量法研究了具有双层介质衬底的平面二维周期性漏波天线的远区辐射场特性。首先根据互易原理,给出了周期漏波天线辐射远场的计算公式;然后采用整域基函数谱域矩量法计算贴片阵列的散射场,利用反射系数考虑了接地介质板的贡献;最后通过实际算例验证该方法的正确性,并分析介质衬底的介电常数、厚度及频率等参数对远区辐射场特性的影响,给出数值结果。     

平直有耗地面上目标地波散射FDTD近一远场外推

由平直有耗地面上垂直电偶极子产生地波场的解析解和互易原理,本文导出了用FDTD方法处理目标地波散射问题时的近一远场外推公式。在数值结果验证了该公式的正确性之后,对海上一金属半球的地波散射场进行了求解,并以此与李清亮等(1997)提出的工程应用方法相对比,考察了工程应用方法的适用性。     

粗糙地面上相邻两树干的电磁散射模型

用有限长多层介质圆柱模拟实际的树干,建立了基于粗糙地面上相邻两树干电磁散射模型。用迭代方法和等效原理,求解了多层介质圆柱的散射矩阵。用互易原理求解了相邻有限长多层介质圆柱包括其二次散射场在内的解析表达式。     

用改进的全波方法分析圆对称层状贴片结构

本文将矢量Hankel变换与谱域导抗法相结合，改进了一种分析圆对称层状结构的全波方法，使理论建模和数值计算都得以简化。该方法应用于微带圆贴片谐振特性的计算，其结果与文献所载的实验数据相符；将该方法应用于费涅尔区板（FZP）透镜焦区场的计算，论证了双层透镜能增强聚焦作用的设计原理。     

随机分布树干层中球的电磁散射

本文用随机分布的有限长多层介质圆柱模拟树干层,用互易原理得到了位于粗糙地面上有限长多层介质圆柱与球目标的二阶散射场近似解析表达式.在L、C、X波段下,研究了位于此环境中金属球目标与周围树干相互作用的电磁散射,计算结果表明,在低频段时树干对目标影响大,低频段可以穿透植被层并应用于目标探测和识别.     

任意取向多个介质旋转椭球的散射场

本文提出了一种用于计算任意取向多个介质椭球电磁散射的混合方法.利用扩展边界条件(EBC)导出具有旋转轴对称单个椭球以球面波矢量函数为基底的T矩阵,结合球矢量波函数旋转定理和递推T矩阵方法,给出多个任意取向介质椭球的散射场.数值例子验证了该混合方法的计算精度和有效性.     

两层旋电磁介质球电磁散射的球矢量波函数解

在均匀旋电磁介质球矢量波函数的基础上,利用球Bessel函数的特性,给出了两层旋电磁介质球内的电磁场用波函数表示的表达式. 在平面波入射情况下,应用电磁场在球边界上切向电场和磁场连续与远区辐射条件,导出了两层各向异性旋电磁介质中电磁场用矢量波函数表示的展开函数所满足的方程组,求出了两层旋电磁介质球的散射场用均匀各向同性波函数展开的展开系数,进而得出了两层旋电磁介质球对平面波的电磁散射特性. 理论分析和数值计算的结果表明:当两层旋电磁介质球的媒质参数相同时,本文所得的结果可退化为单层各向异性旋电磁体解析解.

     

求解目标地波散射特性的方法研究

本文把求解半空间散射问题的FDTD技术与地波传播理论相结合，研究任意复杂目标的地波散特性。入射地波设置在FDTD计算区域中的总场边界上并在散射场输出边界面上提取散射近场数据，然后利用等效及镜像原理，计算无地波衰减时的远区散射场，通过引入地波衰减因子，把该远区散射场转换为远区地波散射场，文中给出了方法验证例子以及一个较复杂目标的单站RCS计算结果。     

龙伯透镜天线的原理及其研究进展

龙伯透镜天线是一种折射率渐变的透镜天线,可将特定频率的入射波汇聚到透镜表面的某点或将电磁波沿原方向反射,能够实现波束扫描和多波束聚焦,已用于电子对抗、第五代移动通信技术、卫星通信以及军用战机和舰艇.介绍了龙伯透镜天线的基础理论,归纳梳理了球形龙伯透镜天线和变形龙伯透镜天线,总结了三种制备技术,对比了不同类型的透镜天线性能,并分析了馈源对龙伯透镜性能的影响,最后对龙伯透镜天线的发展提出建议.     

Radiation pattern computation of a spherical lens using Mie series

The radiation pattern of a sphericai layered dielectric lens is computed using eigenfunction expansions. The method is an adaptation of the well-known classical solution for plane wave scattering from a layered sphere but uses the less well-known vector addition theorem for spherical wave functions to represent the off-center sources. The usefulness of this formulation is that the solution is analytical and "exact," and is an efficient tool for investigating spherical lens radiation properties. The method is illustrated for a typical Luneburg lens.     

介质覆盖导电球上缝隙天线的辐射

给出了用位函数方法推导介质覆盖导电球上缝隙天线辐射场严格解的过程.基于球Hankel函数加法定理,将基本磁流源激励的场展开为以球心为原点的球面波的叠加.利用球矢量波函数的定义及性质,提取出场的径向分量,将初级场分解为相对于径向的TE波和TM波,避免了复杂的矢量微分运算.在此基础上依据散射叠加原理,构造出各区域中场的一般表示形式,其中待定系数直接由球面分层介质中波的反射和透射规律给出.作为实际应用的例子,给出了介质覆盖导电球上均匀环缝问题的计算结果,并对结果进行了分析.     

Scattering of Spherically and Hemispherically Stratified Lenses Fed by Any Real Source

An analytical method to compute the scattering of spherically and hemispherically stratified lens antennas is described. The expansion of any real source on spherical wave functions is detailed and validated by comparison to commercial software simulations and measurements at both 50 GHz and 77 GHz. A mode matching technique (MMT) based on spherical wave functions is first used to analyze the scattering by spherically stratified lens antennas. The far field patterns and directivity obtained are in excellent agreement with commercial software simulations and measurements for a six-shell Luneburg lens at 6 GHz. This MMT is then extended to hemispherically stratified lens antenna analysis. Its validation is also carried out by comparisons to both commercial software and measurements for a three-shell half Maxwell fish-eye lens fed by an open-ended waveguide at W-band. The expansion on spherical modes gives direct access to the field everywhere. To highlight the progressive focusing effect of inhomogeneous lens antennas, the electric field is mapped in terms of magnitude and phase in the neighborhood of the entire structure. One of the originalities of this work is the quantification of the reaction created by the scatterer on the feed. Narrowing the scatterer to a stratified lens does not affect the generality of the presented procedure. While providing controlled accuracy, the MMT tremendously reduces both computation time and memory load in comparison to commercial software.     

Analytical solution for early-time transient radiation frompulse-excited parabolic reflector antennas

A closed-form analytical solution is developed for predicting the early-time transient electromagnetic fields which are generated by a perfectly conducting parabolic reflector antenna when it is illuminated by a transient step spherical wave due to an elemental Huygen's source located at the focus. This closed-form time-domain solution, which is valid both near and far from the reflector (and anywhere in the forward region) can be used via the convolution theorem to efficiently obtain the early-time transient fields generated by the same parabolic reflector antenna when it is illuminated by a realistic finite-energy pulse which emanates as a spherical wave from the focus. The transient solution is developed here by analytically inverting, in closed form, the corresponding frequency-domain solution in terms of a radiation integral that employs an asymptotic high-frequency geometrical optics (GO)-based approximation for the fields in the aperture. Numerical results are presented for the transient fields both near and far from the reflector. The fields on boresight exhibit an impulse-like behavior similar to that of the impulse radiating antenna (IRA) introduced by Baum et al. (1989, 1993)     

A direct derivation of a single-antenna reciprocity relation for the time domain

In this paper, a single-antenna reciprocity relation is derived for the time domain. First, the antenna is considered on transmission; next, the same antenna is considered when it is receiving an incident plane wave. The two states, transmission and reception, are related by the application of a modified form of the reciprocity theorem for electromagnetic fields with general time dependence due to Cheo. The derivation of the reciprocity relation for the antenna makes use of simple geometric arguments to evaluate the spatial/temporal integrals that occur in the theorem. A few extensions of the reciprocity relation are also described.     

Finite-element analysis of complex axisymmetric radiatingstructures

A finite-element method (FEM) is developed for the analysis of complex axisymmetric radiating structures. The method is based on the electric field formulation with the transverse field expanded in terms of edge-based vector basis functions and the azimuth component expanded using nodal-based scalar basis functions. This mixed representation of the electric field eliminates spurious solutions and permits an easy treatment of boundary conditions on conducting surfaces as well as across material interfaces. The FEM mesh is truncated using a previously developed cylindrical perfectly matched layer (PML). The method has been successfully applied to three radiating structures: a corrugated horn antenna, a spherical Luneburg lens, and a half Maxwell fish eye. Numerical results are presented to show the validity, accuracy, and efficiency of the method     

Nonuniform Luneburg and two-shell lens antennas: radiationcharacteristics and design optimization

Design optimization of radially nonuniform spherical lens antennas is the focus of this paper. In particular, special attention is given to the optimal design of nonuniform Luneburg (1964) lens antennas. One of the important engineering objectives of designing an optimal Luneburg lens antenna is to use as small number of shells as possible while maintaining an acceptable gain and sidelobe performance. In a typical radially uniform design, by reducing the number of shells, the gain is decreased and the grating lobes are increased. This deficiency in the radiation performance of the uniform lens antenna can be overcome by designing the nonuniform lens antenna. This necessitates the optimum selection of each layer thickness and permittivity. A genetic algorithm (GA) optimizer with adaptive cost function is implemented to obtain the optimal design. In this manner, the GA optimizer simultaneously determines the optimal material and its thickness for each shell by controlling the gain and sidelobes envelope of the radiation pattern. Various lens geometries, including air gaps and feed offset from the lens surface, are analyzed by using the dyadic Green's functions of the multilayered dielectric sphere. Many useful engineering design guidelines have been suggested for the optimum construction of the lens. The results have been satisfactory and demonstrate the utility of the GA/adaptive cost-function algorithm. Additionally, the radiation characteristics of a novel two-shell lens antenna have been studied, and its performance is compared to the Luneburg lens     

Réponse d’une antenne de réception à une onde incidente non plane

This paper is devoted to the determination of the power coupling factor between an arbitrary incident wave and the load of an antenna illuminated by this wave. The coupling factor is deduced, by means of reciprocity theorem, from the equivalent schema of the antenna. The power delivered to the load is expressed as a function of the spherical wave angular spectrum related to the incident wave and of the radiation characteristic of the antenna in emitting situation. The expression of the coupling factor is well suited for discussing the influence of various parameters and giving conditions for optimal coupling.