基于FEKO和MATLAB GUI的天线布局快速分析处理软件设计

FEKO作为一种分析复杂电大尺寸电磁问题的常用软件,常用于整机天线布局分析。但是由于其模型电尺寸超大,网格数量超多,导致后处理效率非常低。天线不同状态下方向图对比显示、不同天线间耦合度结果显示等,处理过程非常耗时。为了解决该问题,文章设计了一款基于MATLAB GUI的快速处理软件。通过读入FEKO输出文件（场文件.ffe和S参数文件.sNp）,软件可以根据用户要求,快速完成相关结果的绘图输出和统计。同时,软件还实现了文件的自动化分析报告输出,大大提高了工作效率。另一方面,软件还实现了快速建模及设置,以及模型多任务并行仿真计算,降低了用户对仿真软件和电磁算法的熟知要求。     

舰载多天线系统电磁兼容性分析

针对舰载多天线系统电磁兼容性(EMC)分析计算量大、耗时过长问题,提出了自动分层的多层快速多极子方法(MLFMA).采用BiCGStab(l)结合近场预条件方法进行求解,进一步提高了MLFMA的综合效率.为了分析天线间的近场耦合特性,运用微波网络理论结合互易定理给出了任意天线间的隔离度表达式.计算并分析了尺度与真实尺寸相当的某舰船模型上多根超短波天线的辐射方向图和天线间的隔离度.数值结果表明算法准确有效,并且对于电大运载平台中天线布局优化具有一定的指导意义.     

一种有效的天线三维辐射方向图计算方法

提出了一种根据已知的天线E面和H面方向图计算天线的三维辐射方向图的近似算法.以全向和定向天线为例,仿真比较了此算法和两种已有算法计算得到的天线三维辐射方向图与理论结果之间的误差.结果表明,该算法误差较小,可以有效地计算天线的三维辐射方向图.根据生成的三维辐射方向图,计算了天线的方向性系数,所得结果与理论值吻合良好.     

基于并行技术的机载多天线耦合快速算法

分析机载天线间的干扰情况必须首先解决电大尺寸电磁计算问题.首先讨论一种基于空域分解技术及局域网技术的并行数值算法,这种算法将一个电大尺寸散射体表面划分为一系列子域分别进行处理,在求解子域电流的过程中使用了快速多极子技术进行加速运算,然后运用这种算法对机载天线间的耦合进行分析并对算法的性能进行了总结.     

耦合激励系数及对称振子阵列天线的有源方向图研究

为了深入探讨相控阵天线单元间的耦合对阵中单元方向图的影响,以阵列天线单元S参数为基础,给出了阵列天线单元的耦合激励系数计算公式,利用阵列天线单元间的耦合激励系数分析计算阵中单元的有源辐射方向图.同时利用矩量法分析由偶极子单元组成的阵列,并把阵列中每个单元的感应电流幅度和相位与耦合激励系数的幅度和相位进行比较,二者数据基本一致.矩量法计算的单元有源方向图与本文提出方法的计算结果吻合良好,验证了本文给出的阵列耦合激励系数及阵列天线阵中单元有源方向图计算方法的可靠性.     

GTD分析阵列天线在复杂电磁环境下的近场受扰

给出了应用几何绕射理论(GTD)分析计算机载电大尺寸阵列天线方向图的一种方法,比较好地解决了在复杂电磁环境下,大型阵列天线近场受扰分析的问题.该方法将阵列天线的每个阵元看成电偶极子,由于电偶极子尺寸很小,因而可以认为阵列的近场区仍然是单个电偶极子的远场区.根据这样的远场近似,可以利用几何绕射理论用解析方法计算每个电偶极子受到遮挡影响的场分布.通过独立地对阵列天线的每个阵元单独寻迹计算,并且将所有阵元的场进行叠加,就可以得到整个阵列天线受到处于近场的障碍物遮挡影响的场分布.应用此方法计算了一个阵列天线受到近场遮挡之后的方向图,并与应用HFSS仿真软件计算的结果进行了比较.计算结果表明,这一方法可以很好地应用于复杂电磁环境中大型阵列天线的近场受扰问题分析.     

舰载多天线系统的耦合特性分析及防护

为解决舰载多天线系统间的电磁干扰问题,应用FEKO仿真软件进行了舰船与天线的全尺寸仿真模型;基于S参数原理与微波网络理论,给出了多天线系统的耦合度表达式;并分别计算了自由空间与舰船载体2种情况下,多天线耦合度的变化规律。结果表明,谐波、天线间距、天线频率及天线周围散射体是影响舰载多天线耦合特性的因素。并基于上述研究,给出了相应的电磁防护建议。本文研究成果可为后续共享铁塔电磁兼容性分析及多天线布局优化提供参考。     

偏馈抛物面天线方向图外场测试分析

基于口径场法,提出了地基偏馈抛物面天线方向图的数值计算模型,分别给出了自由空间和镜面多径反射情况下的偏馈抛物面天线方向图,分析了测试距离对水平和垂直方向图的波瓣分布和增益的影响;同时分别仿真了固定测试距离情况下,偏馈抛物面天线镜面反射方向图随仰角和高度的变化规律.外场测试结果验证了仿真模型的正确性.该仿真模型能解释不同测试条件下,天线外场方向图的波瓣分布特点,对天线外场测试设计、性能评估和测试误差分析有一定的指导意义.     

大规模阵列天线方向图成形预编码性能仿真*

大规模阵列天线技术可用于解决下一代无线通信的频谱有效性和功率有效性问题,对大规模阵列天线成形性能进行了仿真,得出了天线数目增加对均匀线阵方向图成形的影响,并通过计算比较了不同规模天线阵列的波瓣宽度,并仿真分析了不同规模均匀圆阵的方向图,最后研究了信道估计准确度对大规模天线阵列方向图成形性能的影响,仿真得出了信道估计矩阵存在误差时阵列天线方向图的变化。     

一种抑制多径影响的全向高增益天线

为抑制机载异形地板多径效应对天线方向图的影响,本文提出了一种抑制多径影响的全向高增益垂直极化天线.该天线由四个对称分布的蝶形电偶极子单元构成,阵子臂采用渐变结构来展宽带宽.蝶形电偶极子依次布置于微带地板走线两侧,可优化水平面方向图不圆度.设置四个垂直分布的蝶形电偶极子的馈电相位来降低天线方向图的打地电平,进而抑制地板多径效应的影响.通过理论分析及电磁仿真计算,确定了天线的最优结构以及单元馈电相位差,并进行了实物加工和测量.实测结果表明,在约束尺寸下四单元相位差为25°时能够有效抑制由y轴长地板引起的多径零深,实测与仿真结果吻合较好.该天线的提出为安装于异形地板上的高增益天线阵提供了一种抑制多径影响的方案.     

A diagonalized multilevel fast multipole method with spherical harmonics expansion of the k-space Integrals

Diagonalization of the fast multipole method (FMM) for the Helmholtz equation is usually achieved by expanding the multipole representation in propagating plane waves. The resulting k-space integral over the Ewald sphere is numerically evaluated. Storing the k-space quadrature samples of the method of moments (MoM) basis functions constitutes a large portion of the overall memory requirements of the resulting algorithm for solving the integral equations of scattering and radiation problems. In this paper, it is proposed to expand the k-space representation of the basis functions by spherical harmonics in order to reduce the sampling redundancy introduced by numerical quadrature rules. Aggregations, plane wave translations, and disaggregations in the realized multilevel fast multipole method (MLFMM) are carried out using the k-space samples of a numerical quadrature rule. However, the incoming plane waves on the finest MLFMM level are expanded in spherical harmonics again. Thus, due to the orthonormality of spherical harmonics, the testing integrals for the individual testing functions are simplified into series over products of spherical harmonics expansion coefficients. Overall, the resulting MLFMM can save a considerable amount of memory without compromising accuracy and numerical speed.     

Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis

In this paper, we introduce an approach to analyze the interaction between antennas and the propagation channel. We study both the antennas and the propagation channel by means of the spherical vector wave mode expansion of the electromagnetic field. Then we use the expansion coefficients to study some properties of general antennas in those fields by means of the antenna scattering matrix. The focus is on the spatio-polar characterization of antennas, channels and their interactions. We provide closed form expressions for the covariance of the field multimodes as function of the power angle spectrum (PAS) and the channel cross-polarization ratio (XPR). A new interpretation of the mean effective gains (MEG) of antennas is also provided. The maximum MEG is obtained by conjugate mode matching between the antennas and the channel; we also prove the (intuitive) results that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector modes.      

导体球涂覆各向异性铁氧体介质电磁散射的解析解

该文用球矢量波函数对各向异性铁氧体介质涂覆导体球的电磁散射解析解开展研究。各向异性铁氧体介质中电磁场的球矢量波函数解可表示成第一、二、三、四类球矢量波函数之和。根据球Bessel函数的性质,可以得出导体球涂覆各向异性铁氧体介质的球矢量波函数解析解。应用铁氧体与自由空间分界面上电磁场切向连续和在导体球面上切向电场等于零的边界条件以及球矢量波函数切向正交性质,可分别得出铁氧体介质中电磁场和散射场的展开系数。给出了平面波入射情况下的数值计算结果。该文的结果可应用于有关微波器件、天线以及目标特征的分析和计算。     

离轴球形粒子对高斯波束的散射

本文根据广义米氏理论，将入射高斯波束用矢量球谐函数展开，研究离轴球形粒子的电磁（光）散射。获得波束因子／ｇ表达式和它的局域近似结果，以及散射系数ａｎ和ｂｎ的计算公式。讨论了波束宽度和粒子离轴位置对散射系数、消光系数、散射强度角分布，以及对粒子的内场和表面场分布的影响     

Spatial Filtering of MEG Signals for User-Specified Spherical Regions

We introduce a spatial filtering method in the spherical harmonics domain for constraining magnetoencephalographic (MEG) multichannel measurements to any user-specified spherical region of interest (ROI) inside the head. The method relies on a linear transformation of the signal space separation inner coefficients that represent the MEG signal generated by sources located inside the head. The spatial filtering is achieved effectively by constructing a spherical harmonics basis vector that is dependent on the center of the targeted ROI and it does not require any discrete division of the headspace into grids like the traditional MEG spatial filtering approaches. The validation and the performance of the method are demonstrated through both simulated and actual bilateral auditory-evoked data experiments.     

The Exact Analytical Solution for Large Circular Loops Radiating Around a Dielectric Coated Conducting Sphere

In this paper, the electromagnetic field of electrically large circular loop antennas, with different radii and different nonuniform current values, around a dielectric coated conducting sphere is considered. One or more loop antennas are located on the outer surface of a spherical dielectric shell covering a conducting sphere. Eigenfunction series solutions for the field are assumed in two regions. The current distribution on the wire loop, driven by a voltage source, is determined by Fourier series expansion and all necessary harmonics are taken into account. Exact analytical field expressions in closed forms are derived and field patterns are plotted. The antenna model and formulation presented in this paper offer exact analytical solutions to several loop antenna problems.      

多层球对高斯波束的散射

本文根据广义米氏理论，将入射高斯波束用矢量球谐函数展开，研究多层介质球的电磁（光）散射，提出波束因子ｇｎ的改进算法以及散射系数ａｎ和ｂｎ的迭代公式和算法，并进行了数值计算与讨论。     

Application of on-surface MEI method on wire antennas

The formulas of the on-surface measured equation of invariance (OSMEI) for wire antennas are derived. The unknowns of each node on the antenna surface are expressed by the vector potential function and surface current density. The unknowns in the vicinity of each node are coupled in a linear equation and the coefficients of the linear equation are determined by the measured equation of invariance (MEI) method. The final impedance matrix obtained by the OSMEI is a highly sparse matrix. It demonstrates that the currents on thin wire antennas may also be solved by a differential equation-based formulation in addition to the conventional integral equations     

Directional Estimation of Block-Fading MIMO Channels Using Spherical Harmonics Expansion and Tensor Analysis

The well-known benefits of multiple input multiple output (MIMO) wireless communication systems suppose an efficient use of spatial diversity at both the transmitter and receiver. An important and not well-explored path toward improving MIMO system performance using spatial diversity takes into account the interactions among the antennas and the (physical) propagation medium. In this work, spherical harmonics and tensor analysis are originally combined into the problem of MIMO channel modeling and estimation. The use of spherical harmonics allows to represent the antenna radiation patterns in terms of coefficients of an expansion of spatially orthogonal functions, thus decoupling the transmit and receive antenna array responses from the physical propagation medium. Assuming a single-scattering propagation scenario driven by a finite number of specular multipaths, the parallel factor model is used to decompose the spherical modes of the MIMO channel into a sum of rank-one spherical mode tensors, whose dimensions are transmit modes, receive modes, and time. Then, we extend the tensor modeling framework to double scattering channels by resorting to the PARATUCK model that captures the interactions between multiple-scattering clusters. Capitalizing on the structure of these tensor models, we derive tensor-based alternating least squares algorithms for estimating directional MIMO channels in the spherical harmonics domain, from which the directions of arrival and directions of departure are extracted by means of a MUSIC-based method. Simulation results are provided to assess the performance of the proposed algorithms in selected system configurations. Our results also show the impact of the spherical expansion order on the accuracy of DoD/DoA estimates using the proposed algorithms.     

辐射体声场计算的综合Helmholtz积分公式法

提出了一种计算无界声媒质空间中任意形状辐射体辐射声场的新方法——综合Helmholtz积分公式法(Synthetic Helmholtz Integral Equation Formulation,SHIEF)。该方法将关于辐射体的内部、表面和外部Helmholtz积分方程有机地组合在一起,在已知辐射体表面法向振速的条件下,求出辐射体表面的声压分布,进而求其辐射声场分布。运用该方法计算分析了脉动球相对辐射阻抗随相对半径的变化情况,通过与理论值以及已有的其他方法(例如联立Helmholtz积分公式法(CHIEF)、超定外部Helmholtz积分公式法等)的比较,证明了该方法的正确性、准确性以及快速性,该方法有效地克服了CHIEF法和超定外部Helmholtz积分公式法的缺点。