天线罩加载问题的矩量法仿真与计算

研究天线罩系统在各类飞行器上应用非常广泛.为了保护天线免受恶劣环境的损坏,克服天线辐射引起误差,根据RWG基矩量法(MOM),用计算机仿真分析了天线罩加载后整套天线系统的辐射性能.首先,从表面积分方程(SIE)出发,利用等效原理结合矩量法对目标进行了严格的理论建模,推导出适合编程求解的矩阵方程.通过数值仿真,证明了算法的有效性.最后分别分析了加载体、天线罩对天线辐射性能的影响,并计算了加载复杂模型时天线系统的辐射场分布.证明方法可以改善任意形状加载体对天线系统的辐射影响.     

P 波段抛物柱面天线的矩量法分析

应用矩量法对波长为0. 70 m 的P 波段抛物柱面天线进行了分析和计算, 该天线的馈源由7 元半波振子阵列构成。分析了馈源阵列偏离抛物柱面焦线时对天线增益、输入阻抗等性能的影响。计算表明, 馈源阵列沿径向向内偏离焦线时, 主要对天线的前后比产生影响, 沿径向向外偏离焦线时,对天线的主瓣和前后比都产生影响。此时, 天线输入阻抗的变化比方向图的变化明显。同样, 馈源振子直径的变化对方向图的影响较小, 而对输入阻抗的影响则较大。还对天线的波束扫描进行了模拟。     

天线及其放大器的工作原理与选用原则

天线部分一、天线的种类天线是电视接收系统的第一大件,电视接收天线的类型较多,如基本半波振子天线、折合振子天线、多单元引向天线、菱形天线、对数周期天线、框形天线……等,其中应用最广的应属基本半被振子天线、折合振子天线与多单元引向天线,这里就其外形与尺寸作介绍。 1、基本半波振子天线;基本半波振子天线的结构比较简单,如图1所示,振子采用管径8mm—20mm的     

基于HALLEN方程法的半波天线的参数计算

在现代电磁工程中,对于边界不复杂的问题,可用解析法得到精准解,但较复杂的边值问题用解析法不能得到解答,需要数值法。在此导出HALLEN方程法,用MATLAB软件实现,它能够非常接近解析值,说明其正确性。矩量法是求解电磁场边界值问题中一种行之有效的数值方法 ,利用矩量法将HALLEN法的积分方程化为差分方程,将积分方程中积分化为有限求和,从而建立代数方程组,用MATLAB编程进行数值计算和仿真。最后得出结论 ,矩量法分析能够接近其解析解,说明其正确性。     

导体电磁散射问题的H~2矩阵快速求解算法

根据理想导体的边界条件建立线、面连接结构的电场积分方程。该积分方程运用矩量法直接进行计算时,随着电尺寸增大,计算量和存储量就会迅速增加,进而降低了求解的效率。为了降低计算量和存储量,运用H2矩阵方法的可容许条件将阻抗矩阵元素划分为远区场的矩阵块和近区场的矩阵块。近区场的矩阵块直接用矩量法计算并进行存储,远区场的矩阵块通过H2矩阵的层间插值的方法进行处理并存储,从而有效地降低了计算量和存储量。     

基于外场场强测量的短波天线辐射效率监测

针对短波天线辐射效率难以现场监测的问题,研究一种基于外场场强测量的短波天线辐射效率监测方法。该方法结合天线仿真与测量技术,通过域变换法解析介质半空间位型并矢格林函数,采用RWG矩量法(RWG-MoM)离散平面分层介质C类混合位电场积分方程（MPIE）,得到天线辐射功率的相对分布。测量天线外场场强,得到场点电磁功率面密度作为样本估计天线辐射功率,由辐射功率与输入功率的比值计算得到天线辐射效率。以短波双极天线为例,基于现有的飞艇场强测量平台,进行室外远场场强的测量,实验得到的归一化场强方向图与仿真结果吻合较好,通过该方法计算得到的天线辐射效率与公开文献一致性较好,实现了短波天线辐射效率的监测。     

基于PSO方法的智能天线广播波束赋形设计

研究智能天线性能优化问题,为了快速、准确的对智能天线广播波束设计,提出了一种矩量法和粒子群优化相结合的混合方法.采用基于RWG基函数的矩量法对TD-SCDMA板状振子型智能天线阵进行了全波分析,并使用粒子群优化方法设计了智能天线的波束形状.采用MOM全波分析方法作为优化过程的计算核,既考虑了阵列单元间的相互耦合,又考虑了天线的实际形状,综合出了TD-SCDMA智能天线阵列单元的激励幅度和相位.结果表明,混合方法结合天线单元间互耦能够快速、准确的计算出所需要的理想波束,新方法具有实用性,为波束赋形的工程设计提供了依据.     

一种基于Koch和Hilbert分形加载的电子标签天线设计

研究了不同角度、不同阶数的基于Koch曲线的天线性能,仿真和测试结果表明,在保持天线长度不变的条件下,随着角度和阶数的增加,天线的谐振频率下降,而天线的方向图依然具有半波振子的低方向性。在此基础上,综合Koch和Hilbert曲线,设计了一款尺寸为55mm×10mm的小型化电子标签。该标签天线不仅具有半波阵子的低方向性,而且简单、便于调谐。     

新型缝隙加载平面等角螺旋天线分析与设计

文章给出了一种新型结构的缝隙加栽平面等角螺旋天线，该天线采用基于自补结构并附加缝隙的平面等角螺旋振子组成，采用矩量法对缝隙位置进行优化以改善天线的阻抗特性。根据等角螺旋天线的特性，采用一种阻抗为指数渐变的微带线——平行双线形式的宽带巴仑，并采用50Ω同轴线馈电。仿真及测试结果表明该天线具有良好的宽带特性。     

旋转对称矩量法高阶算法研究

直接应用三维矩量法求解旋转对称目标的电磁散射特性计算效率较低,计算机内存耗费大,利用其结构特点可降维获得一种更为有效的计算方式。然而对于电大目标,这种改进依然是不够的。文中根据旋转对称目标矩量法（ BOR-MOM）中电流的分解特征,构建了一种基于切比雪夫近似的高阶基函数,将电流的切向分量和方位角分量分别以该高阶基函数展开后应用矩量法求解。实验结果表明：高阶BOR-MOM算法在低剖分下,具有很高的计算精度,计算效率和存储耗费得到了较大改善。     

海中低频水平磁偶极子在空气中产生的电磁场

采用电磁波进行跨海水-空气界面通讯时,合理的天线形式是影响通信性能的重要因素之一。为了研究环形天线在跨海水-空气界面通讯中的特点,根据磁偶极子性能,考虑海底-海水-空气三层各向同性的分层模型,推导出置于海水中的水平磁偶极子空气中激发的电磁场分量的解析表达式。进一步采用数值方法,计算了顶层空气中电磁场的分布和传播规律。结果表明,海水中的低频水平磁偶极子在空气中激发的电磁场的各个分量在垂直面内有不同的方向性,且在距发射源较近时有快速的衰减,随着距离增大,衰减逐渐减缓,但在一定高度和水平范围内有可测量的量级,说明环形天线在此类型通讯中是可行的。     

Planar antenna beam deflection using low‐loss metamaterial for future 5G applications

A method to tilt the beam of a planar antenna in the E‐plane is demonstrated by implementing a metamaterial (MM) structure onto the antenna substrate at the fifth‐generation (5G) band of 3.5 GHz. The beam tilting is achieved due to the phase change that occurs when the electromagnetic (EM) wave traverses through two media with different refractive indices. A new adjacent square‐shaped resonator (ASSR) structure is proposed to achieve the beam tilting in a dipole antenna. This structure provides a very low loss of ?0.2 dB at 3.17 GHz. The simulation and measurement results illustrate that the radiation beam of the dipole antenna is tilted by +25° and ?24° depending on the position of the ASSR array onto the dipole antenna substrate. In addition, no degradation in the gain is observed as in the conventional beam‐tilting methods; in fact, gain enhancement values of 3 dB (positive deflection) and 2.7 dB (negative deflection) are obtained compared with that of a dipole antenna with no ASSR array. The reflection coefficient of the dipole antenna with ASSR array has a good agreement with that of the dipole antenna with no ASSR array. The measured results agree well with the simulated ones.     

ADAMANT: A surface and volume integral-equation solver for the analysis and design of helicon plasma sources

We present a full-wave numerical tool, dubbed ADAMANT (Advanced coDe for Anisotropic Media and ANTennas), devised for the analysis and design of radiofrequency antennas which drive the discharge in helicon plasma sources. ADAMANT relies on a set of coupled surface and volume integral equations in which the unknowns are the surface electric current density on the antenna conductors and the volume polarization current within the plasma. The latter can be inhomogeneous and anisotropic whereas the antenna can have arbitrary shape. The set of integral equations is solved numerically through the Method of Moments with sub-sectional surface and volume vector basis functions. This approach allows the accurate evaluation of the current distribution on the antenna and in the plasma as well as the antenna input impedance, a parameter crucial for the design of the feeding and matching network. We report several numerical examples which serve to validate ADAMANT against other well-established numerical approaches as well as experimental data. The numerical accuracy of the computed solution versus the number of basis functions in the plasma is also assessed. Finally, we employ ADAMANT to characterize the antenna of a real-life helicon plasma source.     

Printed radiating structures and transitions in multilayered substrates

This article reviews an integral equation technique to efficiently solve printed structures consisting of conducting patches, slots, and ground planes residing in a stratified medium. The integral equation is cast into a mixed potential form and solved in the space domain. Both the electric and magnetic surface currents are considered as general two-dimensional surface currents with no prescribed or preferred direction. Thus, arbitrary shapes for patches and slots can be considered. After the formulation in the space domain, the integral equation is solved using the method of moments. Theoretical results are compared with measurements for three structures. These structures are: a wide slot antenna excited by a microstrip line; a microstrip line-slot line-microstrip line transition; and transitions between microstrip lines embedded at different levels of a multilayered media. © 1992 John Wiley & Sons, Inc.     

Recursive algorithm and accurate computation of dyadic Green’s functions for stratified uniaxial anisotropic media

A recursive algorithm is adopted for the computation of dyadic Green＇s functions in three-dimensional stratified uniaxial anisotropic media with arbitrary number of layers. Three linear equation groups for computing the coefficients of the Sommerfeld integrals are obtained according to the continuity condition of electric and magnetic fields across the interface between different layers, which are in correspondence with the TM wave produced by a vertical unit electric dipole and the TE or TM wave produced by a horizontal unit electric dipole, respectively. All the linear equation groups can be solved via the recursive algorithm. The dyadic Green＇s functions with source point and field point being in any layer can be conveniently obtained by merely changing the position of the elements within the source term of the linear equation groups. The problem of singularities occurring in the Sommerfeld integrals is efficiently solved by deforming the integration path in the complex plane. The expression of the dyadic Green＇s functions provided by this paper is terse in form and is easy to be programmed, and it does not overflow. Theoretical analysis and numerical examples show the accuracy and effectivity of the algorithm.     

高阻抗表面的反射特性研究

利用高阻抗表面作偶极子天线反射基板,分析高阻抗表面的反射特性。与普通金属板使反射波与入射波相位相差180o比较,高阻抗表面能实现一定频带内的同相位反射。根据这一原理,设计低剖面偶极子天线,使天线的工作频率处于电磁带隙的谐振频率上,从而使高阻抗表面反射后的电磁波与天线的辐射波同相叠加,提高天线的辐射效率。利用HFSS仿真TE极化和TM极化下高阻抗表面反射相位随入射角的变化,结果表明：高阻抗表面在两种极化方式下呈现的相位反射不同。     

Passive intermodulation of printed dipole antennas: Modeling,evaluation, and experiment

A theoretical treatment of electro‐thermally induced passive intermodulation (PIM) is developed for printed dipole antennas, yielding an expression of third‐order intermodulation distortion based on the surface current distribution. The simulation procedure of third‐order PIM products with the full‐wave frequency‐domain method was given to evaluate the PIM level. In particular, the PIM dependencies on input power, two‐tone frequency separation, and substrate parameters are analyzed leading to design guidelines for low distortion antennas. It is shown in this paper that the thermal factors have a noticeable impact on the PIM power generated by printed dipole antennas. Finally, two antenna samples are fabricated on different substrates, Rogers 5880 and FR4, and a two‐tone test at 2‐GHz band using a reflective PIM test system is reported. The PIM evaluation method and the design guidelines to reduce the PIM on printed antennas proposed in this paper are of great significance for telecommunication systems.     

A closed‐form analysis of printed wide‐slot antennas

A mixed‐potential integral equation is formulated for the wide‐slot antenna, fed by a microstrip line, and solved using the method of moments (MoM). Our MoM implementation makes use of the Ge and Esselle (G–E) closed‐form Green's functions for layered substrates. The key advantage of this new approach is that all the MoM matrix elements are evaluated using closed‐form expressions, without any numerical integration, and with minimal approximations. Hence a significant increase in computational efficiency has been achieved while maintaining the high precision of the full‐wave MoM. The numerical results obtained from the new method are compared with measured results, and good agreements are observed. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13, 389–397, 2003.     

A novel broadband magnetoelectric antenna

A broadband antenna based on magnetoelectric dipole is proposed. The proposed antenna is composed of a bowtie‐shaped electric dipole and an elliptical ring antenna that works as a magnetic dipole. For a broadband performance, a microstrip‐to‐coplanar stripline transition balun is used to excite the antenna. All of them are printed on the same plane perpendicular to the ground. To validate the design, prototypes of the proposed antenna have been fabricated and measured. The measurement results show that the antenna has a wide impedance bandwidth of 66.7% (2.45–4.90 GHz) for voltage standing wave ratio (VSWR) less than 2 and a gain of 6.0–7.3 dBi over the operating frequency band. Meanwhile a high front‐to back ratio better than 16 dB over the operating frequency is achieved. The agreements between the simulation and measurement results indicate that the proposed antenna is suitable for wireless communication systems and phased array systems. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:213–218, 2015.     

Solution of Electromagnetic Scattering Problems Involving Three-Dimensional Homogeneous Dielectric Objects by the Single Integral Equation Method

The problem of electromagnetic scattering by a homogeneous dielectric object is usually formulated as a pair of coupled integral equations involving two unknown currents on the surface S of the object. In this paper, however, the problem is formulated as a single integral equation involving one unknown current on S. Unique solution at resonance is obtained by using a combined field integral equation. The single integral equation is solved by the method of moments using a Galerkin test procedure. Numerical results for a dielectric sphere are in good agreement with the exact results. Furthermore, the single integral equation method is shown to have superior convergence speed of iterative solution compared with the coupled integral equations method.