三维TEM喇叭天线瞬态辐射的FDTD模拟

本文应用FDTD方法分析放置于无限大理想导体地面上并由同轴线馈电的TEM喇叭天线瞬态辐射问题。对FDTD计算区域中的细导线结构采用网格共形技术进行了特殊处理,同时引入一维传输线模型模拟同轴线馈电以大大减少FDTD的计算空间,并实现了天线与同轴线相互耦合的FDTD方法。数值结果表明本文方法处理瞬态天线辐射问题的有效性。     

平板宽带单极与偶极天线的全波分析

采用时域有限差分法（FDTD）计算圆盘天线及宽带变形vivaldi天线的输入阻抗及方向图。利用镜像原理得到三角形单极、圆盘单极天线的输入阻抗。采取激励源区的准静态模型在保证精度的同时又无须将复杂的具体馈电结构建模，三角形单极天线和圆盘单极天线的计算结果与有关文献的比较验证了该方法具有准确、实用性强等优点，对宽带变形vivaldi天线FDTD分析得到电流分布及输入阻抗，经傅立叶变换由近场值得到天线远场方向图，结果表明变形vivaldi天线具有输入阻抗和方向图的宽带特性。     

偶极子光电导天线结构对THz 辐射特性影响的研究

研究了GaAs工型偶极子光电导天线(PCA)结构参数对THz辐射特性的影响。首先利用DL(Drude-Lorentz)模型得到了光电导天线的电流解析解,结合时域有限差分(FDTD)进行半解析半数值仿真,有效地解决了纯解析解(通过光电流对时间求导数可以得到辐射的THz的相对强度)无法和PCA结构直接对应的仿真问题,也较直接全波FDTD方法计算效率高。接着,利用偶极子光电导天线的等效电路模型和等效源阻抗公式,结合实际的PCA参数,分别得到了PCA阻抗和源阻抗,说明了由于源阻抗很低,导致匹配效率较低。最后,综合考虑数值仿真结果和理论计算结果可证明,工型偶极子光电导天线的辐射效率会随着其长宽比的增加而相应增加,该结论与相关文献实测结果吻合,从而也验证了文中FDTD仿真结果、理论模型及计算结果的有效性。     

高功率微波作用下单极天线瞬态响应特性研究

运用时域有限差分法(FDTD)结合同轴等效馈电模型计算了高功率微波(HPM)电磁脉冲作用下单极天线的感应电流的频域和时域响应,分析了单根单极天线感应电流频谱和时域响应与入射HPM间的关系,同时分析了两根天线间的距离对第一根天线末端感应电流的影响。计算结果表明,单根单极天线对HPM的感应电流频谱主要由入射HPM载波频率决定,感应电流波形与入射HPM波形相似;有其他天线存在时,对第一根天线会造成影响,且随距离增加影响减小。     

介质平面上高频单极天线特性分析

该文用时域有限差分法(Finite Difference Time Domain,FDTD)计算介质平面上单极天线的阻抗特性。用FDTD法计算天线的辐射特性可以使用不同的激励方式,文章比较了采用不同激励方式时,天线的输入阻抗。文章的主要内容是将表面阻抗法用于FDTD中,计算架设在介质平面上单极天线的辐射特性,并用FDTD法计算了介质平面上铺设不同尺寸的导体平面时,天线的阻抗特性。     

卫星赋形天线矩形同轴线馈电网络的FDTD分析

采用时域有限差分（FDTD）方法分析了构成卫星赋形天线馈电网络（BFN）的矩形同轴线各种不连续性结构的散射特性。该方法通过模拟波的传播过程直接求解结构的散射参数,与模匹配方法相比,分析过程大为简化,将计算结果与实验值进行了比较,二者吻合很好,充分证明了本文方法的有效性和精确性。     

卫星赋形天线矩形同轴线馈电网络的FDTD分析

采用时域有限差分(FDTD)方法分析了构成卫星赋形天线馈电网络(BFN)的矩形同轴线各种不连续性结构的散射特性.该方法通过模拟波的传播过程直接求解结构的散射参数,与模匹配方法相比,分析过程大为简化.将计算结果与实验值进行了比较,二者吻合很好,充分证明了本文方法的有效性和精确性.     

复杂环境中短波天线的MoM/FDTD混合法分析

利用电磁场数值计算方法中的矩量法/时域有限差分（MoM/FDTD）混合方法,分析了复杂环境中短波天线的电磁辐射性能,建立了短波双极天线的自由空间模型。采用矩量法和时域有限差分法相结合,对其模型进行仿真计算,并将计算结果和已有的文献进行比较,验证了混合方法计算结果的可行性、准确性。总结了该模型对短波天线远区场影响的有益经验,为改善短波天线性能提供了设计参考。     

用空间传播和RCS模型研究RFID装置最大识别距离

通过自由空间传播模型和雷达散射横截面（RCS）模型，研究了反向散射射频识别（RFID）装置的最大识别距离。用高频电磁场仿真软件FEKO对折叠偶极子标签天线进行了建模仿真，得到天线的远场辐射方向图、输入阻抗以及在不同负载情况下天线的单站RCS值。经过理论分析和仿真计算，由两个电波传播模型分别得出RFID装置可能的最大识别距离。最后比较了两种模型的计算结果，较小的距离即为该反向散射RFID装置的最大识别距离。     

一种水平全向平面偶极子阵列天线

基于偶极子组阵结构,设计了一种具有水平全向辐射方向图和水平极化特性的平面天线。该天线由3只偶极子天线组成,每只振子弯折30°并上下交错印刷在PCB板的表面上,构成正六边形环,环的直径为0.45λ0(λ0为中心频率处的自由空间波长)。3只偶极子天线均采用SMA接头直接顶馈,从而省略了偶极子天线的馈电巴伦。通过优化偶极子天线振子长度和间距等结构参数,以及控制馈电相位,实现水平全向辐射。设计和加工制作了一只工作频率为2.45 GHz的天线样品,测试与仿真结果吻合良好,其|S11|≤10 dB的相对阻抗带宽为12.94%(2.367~2.684 GHz),水平全向增益约为1.42 dBi,不圆度小于±0.7 dB。     

Hemispherically capped thick cylindrical monopole with a conical feed section

The axis boundary condition scalar potential integral equation is used to study the hemispherically capped thick cylindrical monopole with a conical feed section. The monopole is perfectly conducting and is fed by a coaxial line whose outer radius is connected to an infinite perfectly conducting ground plane. One approximation in the equation is that the field across the coaxial aperture is approximated by the fundamental TEM coaxial line mode. The integral equation is numerically solved by the moments method using entire domain basis functions with delta weights. A simple way for checking the convergence of the solution that needs no new integrations is given. The theoretical current distributions, input admittances, and radiation patterns are given for a thin, moderately thick, and thick monopole with and without a conical feed section. This feeding section simplifies the matching of the antenna to conventional signal generators and improves the high frequency characteristics of the monopole.     

Feed models for coax-driven monopole and dipole antennas

A method is presented for accurately modeling a monopole or dipole antenna fed by a coaxial line. The base of the monopole is attached to a conducting plane through which the coaxial feed line extends to the feed. The feed structures considered are easily adaptable to physically rugged forms and are simple to construct. Equivalent models for the three regions of the structure are devised and coupled integral equations for aperture fields and surface currents are formulated to enforce the boundary conditions. Three variations of the feed configuration are discussed and the reflection coefficient of the antenna feed is determined from the data obtained from the solutions of the coupled integral equations. Computed reflection coefficient values are shown to agree well with values measured on laboratory models.     

一种基于FDTD的简单有效的天线阻抗计算方法

本文从有源区的软激励时Yee差分方程出发,推导了一种适用于理想的间隙激励(δ-gap source)和探针激励的天线输入阻抗新的计算公式,该方法简洁、有效,公式物理意义明确,能够有效地消除硬激励(hard source).计算天线阻抗时,在频率很低接近零时阻抗值的严重失真,使得应用时域有限差分法计算天线输入阻抗变得更加快捷适用.最后,本文应用该方法分别计算了一个单极子天线和同轴馈电的微带天线,单极子天线的计算结果和前人的计算结果吻合得很好,并且消除了频率接近零时以前计算结果的严重失真,微带天线和已有软件的计算结果进行了比较,得到了满意的结果.     

Input admittance of a multilayer insulated monopole antenna

An efficient numerical technique based on the modal-expansion method in conjunction with a recursive algorithm is developed for a multilayer insulated monopole antenna fed by a coaxial transmission line. The modal-expansion analysis is facilitated by introducing a perfectly matched boundary (PMB) at a variable height over the ground plane of the monopole. The current distribution and input admittance are computed by finding the expansion coefficients of the electromagnetic field expressions. Numerical results for the input admittance of a dielectric-coated monopole antenna and an air-insulated monopole are compared with experimental ones available in the literature. Good agreement is achieved. Calculated results for the effects of various parameters on the input admittance of an air-insulated monopole antenna are presented and discussed     

基于柱坐标抛物方程的海上雷达覆盖范围研究

为预测雷达波在海面的全向传播特性,提出了基于柱坐标抛物方程(parabolic equation,PE)的电波传播模型,用于海上雷达覆盖范围的研究.从亥姆霍兹方程出发,推导出柱坐标系下的前向PE形式.再利用PE通解中三角函数的正交性,求解各电波传播模式的激励系数,结合分步傅里叶变换实现柱坐标PE的步进迭代算法,以预测电...     

馈电同轴芯径对微带天线性能的影响

针对同轴线馈电的微带天线,建立了等效电路模型。该等效电路表明,馈入到微带天线内部的导体直径直接影响天线的输入阻抗。为此设计了单频圆极化微带天线,采用电磁计算软件HFSS仿真计算了不同馈电芯径对天线参数的影响,验证了该理论。同时设计了双层介质的双频微带圆极化天线,采用同一个馈点馈电,上层微带介质中馈电导体的直径与下层微带介质中馈电导体直径不同。通过HFSS软件的优化仿真,得到了对应于两个不同频段的最优上下层馈电导体直径,获得了最佳的驻波。研究表明,对于单频和双频微带天线,通过优化馈入到介质中导体的直径可以改善天线的驻波特性。     

On the electrically thick monopole: Part I--Theoretical solution

A new integral equation is formulated for the current distribution of an electrically thick, cylindrical antenna which is driven by a voltage across a finite gap on an infinitely large ground plane. Compared to the conventional integral equation of Hallen, this equation has an additional source term which can be expressed in terms of both the radius of the antenna and the width of the gap. A numerical solution of the integral equation has also been obtained by a so-called "approximate product-integration technique" and the results have been compared with the experimental data of a monopole antenna driven by a coaxial transmission line over an infinitely large ground plane. When the circumference of the antenna is comparable to a free-space wavelength, the experiment verifies that the theoretical model with finite gap excitation describes the experimental situation more properly than either the conventional model of a delta-function excitation on both outside and inside surfaces of the antenna, or the King-Wu model of a delta-fanction excitation only on the outside surface.     

Microwave catheter design

A microwave antenna system for transcatheter ablation of cardiac tissue is investigated. A numerical model based on the finite-difference time-domain method incorporating a Gaussian pulse excitation has been constructed and frequency domain electric and magnetic fields are obtained through Fourier transformation. Results are presented for a coaxial line fed monopole catheter which is modified by the successive inclusion of a Teflon sheath outer coating, a terminating disk at the tip of the antenna, a sleeve choke, and a high dielectric constant cylinder surrounding the monopole antenna. The effects of these design features are characterized in terms of specific absorption rate (SAR) and return loss (RL). Numerical calculations are confirmed by comparing with the RL measurement of a Teflon-coated monopole containing a disk and choke     

等离子体中的涡旋电磁波传播研究

目前对涡旋电磁波的产生方法及应用已经有很多理论及实验上的研究,但对于其传播过程的研究还非常缺乏,尤其是在电离层等离子体中的传播过程的研究. 本文建立了柱坐标系下的时域有限差分方法模型,推导了柱坐标系下的边界吸收方法,在此基础上计算了涡旋电磁波在真空及等离子体中的传播过程,同时模拟了等离子体密度在涡旋电磁波作用下的时空演化过程. 模拟结果表明:通过阵列天线模型产生的涡旋电磁波在真空中传播时涡旋的形状不会改变;在等离子体介质中,涡旋波的传播依然遵循线性理论,当涡旋电磁波遇到截止频率的等离子体时也会有明显的反射,并产生驻波;同时,在等离子体中涡旋波依然可以保持涡旋形态;涡旋波对等离子体的线性作用使得等离子体也呈现出涡旋态,与实验中的观测相符. 以上的模拟结果能为涡旋电磁波加热电离层的实验以及未来在短波通信方面的应用提供理论支持. 本文建立的涡旋波在等离子体中的传播模型也为进一步研究涡旋波与等离子体的非线性相互作用打下了基础.     

计算表面波特征方程的一种新的数值方法

推导了同轴线馈电的微带天线表面波电磁场表达式及其特征方程.结合遗传算法与参数跟踪策略形成一种新的算法,并基于该算法对表面波特征方程进行了精确数值求解,求解结果与本问题的已有结论吻合的很好.该方法具有简单、通用、求解精度高等优点.