A Full Electromagnetic Analysis of Grooved-Dielectric Fresnel Zone Plate Antennas for Microwave and Millimeter-Wave Applications

Grooved-dielectric, phase-correcting, Fresnel zone plate antennas are analyzed using the body-of-revolution finite-difference time-domain (BOR-FDTD) method. Parametric studies of the focusing ability of these antennas are performed to examine the effects of the focal length, diameter, number of zones, and the thickness of the lens, as well as the number of phase corrections per zone. The results of these studies are presented as design graphs and are used to lend insight into the focusing mechanism of phase-correcting zone plates. The BOR-FDTD analysis is validated by comparison with previous measurements.     

微带线天线阻抗的一种通用快速全波分析法

提出了一种通用、高效、高精度的快速全波分析法——渐近提取法,巧妙地利用一种计算机辅助法完成渐近提取法的理论推导。该方法克服了传统推导的诸多困难以及涉及到复杂数学函数多而难以正确处理的缺点,从而使得渐近提取法理论推导简单化。与直接积分法相比,该方法计算互阻抗矩阵时大大地节约了计算时间。最后利用该方法计算微带线天线的阻抗特性及辐射特性,计算结果与文献[1]及HFSS软件仿真结果一致性很好。     

A Systematic Study of Varying Reference Phase in the Design of Circular Fresnel Zone Plate Antennas

A circular Fresnel zone plate antenna was simulated using a finite difference time domain software to study the effect of changing the reference phase from the standard 0deg to any value between 0deg and 180deg. Several prototypes were built to validate the simulations using four different focal-length-to-diameter (F/D) ratios. It was found that a significant improvement in the level of the first sidelobe, up to about 9 dB according to the simulations, could be achieved without sacrificing gain or cross-polarization levels     

基于RWG-MoM金属球表面天线的全波分析

提出了一种新的激励源模型,该模型成功克服了传统RWG函数不能在天线与球体连接处添加馈源的问题,同时,对格林函数进行加减自由空间格林函数的处理,解决当源点和场点接近于或位于球面时收敛慢的问题。通过计算位于球表面的单极子天线输入特性,并与相关文献结果进行了对比,结果表明分析方法的正确性和有效性。最后,分析了位于球表面的探针馈电贴片天线的特性,其分析结果与FEKO仿真结果一致性较好。     

平行板波导CTS 天线的设计与分析

采用传输线理论的方法分析设计了平行板波导CTS 天线。建立平行板波导天线的等效电路模型,利用传输线方 程计算天线上的电压分布、电流分布以及辐射阻抗,进而分析远场的辐射特性。最后用Ansoft HFSS 软件仿真验证了该 方法的正确性。     

车载天线电磁特性及耦合度仿真分析

针对车载天线合理安装位置选取的问题,建立金属舱体全尺寸模型,利用CST微波工作室对处于不同布设位置的天线方向图、反射系数及天线间耦合度进行了仿真分析,并对比了位置变化对不同工作频率天线电磁特性的影响。结果表明：天线靠近金属舱边缘,舱顶金属面下方空间的辐射以及水平方向的增益会增强,天线反射系数变优,天线间的耦合度还会降低;随工作频率的降低,位置变化带来的这种影响会减弱。所得结论可为车载天线安装位置的选取提供理论指导。     

柱状机体/星体与天线间的电磁兼容性

针对常规飞机、卫星等的几何形状,用时域有限差分法(FDTD)分析了圆柱形良导体外形(用以模拟飞机卫星等的机体)对机载/星载天线(文中采用了线天线)辐射特性的影响.通过改变柱形的直径和长度,对天线辐射方向图的变化进行了大量的研究,并得出了一些规律性的结果.该结果对于预测机体和星体与天线的电磁兼容及系统电磁兼容性设计具有参考意义.     

抑制两个偶极子天线电磁耦合的新方法

文中通过分析带缝隙的有限接地导电平面对其上偶极子天线耦合度的影响.提出采用具有双缝隙有限接地导电平面,抑制其上两偶极子天线间电磁耦合的新方法.数值分析结果表明,缝隙长度约为相应发射天线工作波长的1/2时,与单缝隙有限接地导电平面相比较,双缝隙有限接地导电平面抑制其上两偶极子天线间电磁耦合效果较优.     

微带天线全波频域法中的小波应用

本文将小波分析引到微带天线全波频域法的计算中，对矩形微带贴片天线感应电流矩量法的小波计算进行了理论推导。对一矩形微带贴片天线进行了实际计算，并与用脉冲基函数和三角形基函数进行计算得到了结果进行了比较。     

电子束静电折板偏转系统研究

以SDS-3电子束曝光机为基础,用折板结构静电偏转替代直板结构静电偏转,探讨了电子束曝光机折板静电偏转场的电子轨迹与电位分布应满足的要求。导出了折板静电偏转灵敏度与电位分布之间的关系,给出静电偏转像差方程及像差系数。用矢量描写电子轨迹,以积分式表示像差系数,给出了折板结构方程与参量。像差系数适应计算机辅助运算。结果表明,折板结构静电偏完成的图像像差明显优于原直板结构静电偏。提供了静电折板偏转与直板偏转的相关计算数据及摩尔栅条纹图。     

多层微带贴片天线的三维全波分析

提出一种基于３Ｄ－ＦＤＦＤ分析多层微带贴片天线的方法,在计算中有用非均匀网格减少对内存的需要,并且利用Ｇ．Ｍｕｒ’ｓ二阶吸收条件和场平均吸收条件截断网格。利用最小二乘法和压缩存储技术求解稀疏矩阵方程。计算了两种典型馈电的贴片天线,并与已有的结果作了比较,获得较好的一致性。     

Analysis of square Fresnel Zone Plate Lens for dual band detectors

Dust emission is used in space applications for star-formation characterization normally acquired by different detectors operating at Infrared (IR) and sub-millimeter wave (sub-mm wave) frequencies. An integrated dual band detector working at both frequency ranges is described in this paper. The proposed configuration implements a spiral antenna working at sub-millimeter wave frequencies whose design is based on Fresnel zones theory. At the same time, this spiral antenna is used as Fresnel lens to focus IR power (12 μm) into an IR detector. The paper describes the influence of implementing a sub-mm wave spiral antenna based on square Fresnel zones. In particular, the effects on the focal distance and the focal gain at IR frequencies and the radiation features at sub-mm wave frequencies are studied. Furthermore, the importance of the number of Fresnel zones used in the design of the sub-mm spiral antenna is also determined.     

用时域有限差分法对缝隙渐变天线的瞬态电磁场分析

本文用时域有限差分（ＦＤＴＤ）法分析缝隙渐变天线，分析中对天线缝隙边缘场和薄天线衬底采取了特殊的处理方法，求天线的远区辐射场采用了ＦＤＴＤ中近场到远场的变换方法。本文计算出的缝隙渐变天线的辐射方向图和远区辐射场与实验结果比较一致。本文给出了超短电磁脉冲在天线上传播和辐射过程的瞬态直观图象，同时还研究了这种天线衬底厚度、几何尺寸及介电常数对其辐射特性及频带的影响。     

A Novel Offset Fresnel Zone Plate Antenna

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CDR-MAC: A Protocol for Full Exploitation of Directional Antennas in Ad Hoc Wireless Networks

In this paper, we propose a new Medium Access Control (MAC) protocol for full exploitation of directional antennas in wireless networks. The protocol introduces a circular directional transmission of the Request To Send (RTS) control packet, spreading around a station information about the intended communication. The stations that receive the directional RTS, using a simple scheme of tracking the neighbors' directions, defer their transmission toward the beams that could harm the ongoing communication. In this way, the proposed protocol takes advantage of the benefits of directional transmissions as the increase of spatial reuse and of coverage range. Additionally, it reduces the hidden-terminal problem, as well as the deafness problem, two main factors for the decrease of the efficiency of directional transmissions in ad hoc networks. The performance evaluation of the protocol shows that it offers a significant improvement in static, as well as mobile, scenarios, as compared to the performance of the proposed protocols that use omnidirectional or directional transmissions.     

Bandwidth Enhancement of Miniaturized Slot Antennas Using Folded, Complementary, and Self-Complementary Realizations

Folded and self-complementary structures are considered as two effective approaches to increase the bandwidth of miniaturized antennas. A folded realization of a previously reported miniaturized slot antenna is devised and shown to provide more than 100% increase in the bandwidth as compared with that of the miniaturized slot antenna with the same size and efficiency. The complementary pair of the miniaturized folded slot, namely, the folded printed wire is also discussed in this paper. It is shown that the folded slot has a much higher radiation efficiency when compared with its complementary folded wire antenna. Another approach for bandwidth improvement is the implementation of the self-complementary structure of the same miniaturized topology to moderate the frequency dependence of the antenna input impedance. To examine this approach, a folded self-complementary miniature antenna is studied, where further increase in bandwidth is observed. A miniaturized folded slot, its complementary miniaturized folded printed wire, as well as their self-complementary realization, were fabricated and tested. These antennas can fit into a very small rectangular area with dimensions as small as 0.065lambda_o x 0.065lambda_o. While the folded slot ranks the highest in the efficiency/gain, the self-complementary structure falls between the slot and printed wire since it consists of equal proportions of the both slots and strips. A self-complementary H-shape antenna is also introduced to demonstrate that by relaxing the miniaturization to a moderate value, a significant improvement in bandwidth can be accomplished. With yet small dimensions of 0.13lambda_o x 0.24lambda_o, a very wide bandwidth of (2.3:1) is obtained. For the case of no dielectric substrate, even wider bandwidth of (3:1) is achievable.     

螺旋倒相型天线的分析

本文应用反应积分方程，考虑任意倾斜导线间的互阻抗，建立起广义阻抗矩阵，采用矩量法求出该天线的电流分布，进而获得辐射特性及输入阻抗等。计算结果与实测值吻合较好，计算精度令人满意，本文的分析结果对螺旋例相型天线的设计、改进、提高是很有用的     

一种激光折叠腔稳定性分析及设计的新方法

为了对激光谐振腔进行优化设计,运用光学传输矩阵理论,借助V型折叠腔激光器的等效简化模型对该激光腔的稳定性进行了研究.分析了腔长、折叠镜焦距、反射镜曲率半径与系统稳定性的关系,得到以失调量为参数的稳区临界曲线方程,实现了三镜折叠腔型CO2斩光盘式调Q脉冲输出激光器的设计.分析结果表明,对于子腔预先给定的参量,只要另一子腔满足适当的失调量,整个谐振腔就是稳定的.任一子腔内有二个稳定区而非以往研究者提出的一个稳定区,可根据需要选取最佳的稳定点.采用失调量而非g因子作为参数,直接给出稳定区范围和失调误差,使用性好.     

Fresnel区板天线辐射特性的矢量场分析

本文利用矢量场统射理论分析研究Ｆｒｅｓｎｅｌ区板天线的辐射特性，并统一考虑馈源对天线增益、副瓣电平和交叉极化等参数的影响，所做工作适用于透射型和反射型Ｆｒｅｓｎｅｌ区板天线。天线远场方向图的计算和实测结果吻合较好，表明本文建立的Ｆｒｅｓｎｅｌ区板天线矢量场绕射模型的有效性