超宽带脉冲横电磁波喇叭的数值模拟

本文用时域有限差分方法分析和优化了前端是平行板传输线的横电磁波喇叭天线（其激励源是由同轴线馈入的超宽带电磁脉冲），优化了平行板传输线和横电磁波喇叭的尺寸，给出了天线的一些特性参数随频率的变化关系、天线的辐射场分布、天线辐射的能量方向图以及天线长度对增益的影响等。     

FR4基板金属底板共面波导传输线阻抗特性研究

为了提高基于FR4基板的射频电路板天线端口阻抗匹配的性能,利用FDTD方法对基于FR4基板的金属底板共面波导传输线特性阻抗与端口回波损耗进行了计算.在理论分析的基础上,对FR4基板金属底板共面波导传输线进行了实际的加工,加工的基板厚度为1.5mm,中心导带分别为1mm、1.5mm和1.7mm,槽宽分别为0.2mm、0.3mm和0.4mm.利用矢量网络分析仪在1MHz～3GHz频段内对S11进行了测试,从测试结果可以看出,高频部分与理论计算结果比较一致,3种尺寸的金属底板共面波导传输线回波损耗均在-10dB以下,考虑加工误差与焊接工艺,第3种结构的阻抗匹配性能最好.     

圆波导TM01模激励的加平行板圆锥喇叭的理论分析与实验结果

用解析公式对由圆波导TM01模激励的加平行板圆锥喇叭辐射场进行了分析,并采用有限元软件分析了该天线在不同频率的辐射场、反射系数.理论分析与实验结果表明,由圆波导TM01模激励的加平行板圆锥喇叭辐射轴向为极大值的线极化的远场方向图,在频率为5GHz时增益大于21dB,辐射效率约93～94%.     

薄膜印刷折合振子的设计

对基于薄膜结构的印刷折合振子进行了研究,通过垂直过渡宽带巴伦将共面波导变换为共面平行带线对印刷折合振子进行平衡馈电。从仿真结果中可知,这种天线单元具有较宽的带宽,良好的辐射特性,天线性能受薄膜层平整度的影响较小,并且底层的馈电网络采用共面波导传输线,解决了薄膜天线辐射单元与T/R 组件连接的问题。这种天线单元形式的研究对降低大口径轻型可展开天线系统的存储体积、重量和制造成本有重要的意义。     

左手加载共面波导激励槽环天线

基于复合右左手传输线的非线性相移特性,提出了一种左手加载的共面波导激励槽环天线。该天线由四个简化的复合左右手传输线结构单元构成,通过调整单元的并联电感值,可以改变天线的谐振频率和输入阻抗,利用仿真方法分析了天线的性能。结果表明,相比于传统天线,新天线尺寸减小了30.25%,总辐射效率达到98.34%,同时交叉极化比提高了2.9 dB。     

Coplanar waveguide-fed slot-loop antenna with left-handed loading

基于复合右左手传输线的非线性相移特性,提出了一种左手加载的共面波导激励槽环天线.该天线由四个简化的复合左右手传输线结构单元构成,通过调整单元的并联电感值,可以改变天线的谐振频率和输入阻抗,利用仿真方法分析了天线的性能.结果表明,相比于传统天线,新天线尺寸减小了30.25％,总辐射效率达到98.34％,同时交叉极化比提高了2.9 dB.     

圆形槽波导的一种简单分析方法

把圆形槽波导等效成横向传输线网络,用不同的均匀传输线等效圆形槽及两边的平行平板区域,根据横向谐振条件,利用Runge-Kutta数值计算方法,分析了波导的色散关系.得到了归一化截止波长λc/2a与归一化波导尺寸2c/2a,以及传播常数β与频率的关系曲线.该分析过程简单明了,数值分析的结果与相关文献的结论吻合较好,表明这...     

微波着陆系统仰角天线H面方向图的分析与设计

本文论述了微波着陆系统仰角天线的H面赋形方向图的形成方法．振子在带有台阶的平行板波导内激励起多种模式的电磁波，合理调整台阶的尺寸，这些模式的叠加能够得到天线的H面赋形方向图,用文中的方法设计了微波着陆系统仰角天线，其H面方向图达到了技术指标，验证了文中方法的有效性。     

宽带大功率径向波导功率合成器设计

平行板径向波导功率合成器具有工作频带宽,低插入损耗,与放大器和传输线匹配良好,端口隔离度较高,功率容量大等特点。设计了一个1.5kW宽带6路径向波导功率合成器,CST软件仿真结果表明:该合成器在驻波比小于1.1的情况下,其工作频带为1.35~3.3GHz,合成效率达到96%。     

基片集成波导中的混合左右手结构及其应用

混合左右手传输线是一种应用电路实现的新型人工电磁媒质，具有很多新颖的特性．而基片集成波导作为一种新型传输线具有高Q值和低辐射，在毫米波应用中有很大潜力，本文提出了一种把混合左右手传输线结构和基片集成波导结合的方法，并且研究这种结构在频扫天线中的应用．全波仿真结果验证了所提方法的有效性。     

Radiation mechanism of dielectric-rod and Yagi aerials

In order to give a better insight into the radiation mechanism of dielectric-rod and Yagi aerials the problem of the radiation from the free end of a semi-infinite dielectric rod or Yagi transmission line is investigated both theoretically and experimentally. Simple approximate formulas are given for the radiation pattern, the gain, the effective aperture and the beamwidth. Using a digital computer, the field near the free end is calculated and compared with the measured field distribution.     

Analysis of radiation characteristics of a finite-lengthtransmission line using a circuit-concept approach

The radiation phenomenon from a transmission line of finite length is described. Based on the hypothesis of reciprocity between the coupling of an external wave to a transmission line and the radiation from a transmission line, a set of models for both phenomena is implemented using a six-terminal network. The goal is to find out what current is induced in each terminal load of the network. The radiation characteristics of finite-length lines such as radiation fields, radiation power-density, and radiation coefficients are considered. Experiments using both straight lines and bent lines have been performed to validate the theory     

梯度温度气体介质的热辐射传递特性研究

高速导弹光学窗口外存在激波层,为高度不均匀的梯度温度气体介质,针对其中的热辐射传递开展一种有效数值求解方法研究.基于离散传递法的思想,利用光线传输模型寻找导引头探测口径内的视线路径,推衍出激波层的热辐射强度计算模型,并研究此模型所得激波层热辐射噪声与来流参数之间的关系,给出经验公式,结果表明,对于3 ～8 μm红外波段...     

Experimental Studies of the Losses and Radiations Due to Bends in the Goubau Line

The losses due to the bending of the Goubau line (G line) are determined by experiments. The losses are measured for wide ranges of radius of curvature, bending angle, and the transmission frequency. These three variables determine the losses. It is believed that radiation from a surface-wave transmission line system occurs mainly from the bends and horn in the transmission line system. Directional patterns of such radiation were obtained from measurements.     

基于地-线缆耦合的感应电流分析*

高功率、大强度电磁波照射,是飞机在电子对抗中实施电磁干扰的重要手段。在实验室通过电流钳对线缆进行电流注入,从而达到模拟飞机系统间电磁干扰试验的目的。如何从理论上分析照射场在电缆上所感应的电流,是飞机系统间抗扰度实验的重要环节。文章利用有源传输线理论,建立了线缆-大地耦合模型,给出了线缆电流分布与大地电导率、地-线缆高度、线缆长度、线缆两端阻抗以及照射场的频率、幅度等多参数的关系;同时还进行了实测验证。结果表明,理论分析与实测结果基本一致,这为飞机系统间电磁干扰试验的实施提供了必要的理论和数据基础。     

Time-domain near-field analysis of short-pulse antennas .I.Spherical wave (multipole) expansion

The radiation from a time-dependent source distribution in free-space is analyzed using time-domain (TD) spherical wave (multipole) expansion. The multipole moment functions are calculated from the time-dependent source distribution. The series convergence rate in the near and far zone and the bounds on the near-zone reactive field are determined as functions of the source support and of the pulse length. The formulation involves a spherical transmission line representation that can be extended to more general spherical configurations. This formulation also describes the field and energy transmission mechanisms in a physically transparent fashion that will be used in a companion paper to define and explore fundamental concepts such as TD reactive energy and Q and to derive bounds on the antenna properties. Finally, the concepts discussed above are demonstrated numerically for pulsed radiation by a circular current disk     

Full wave characterization of a through hole via using thematrix-penciled moment method

A full wave analysis was presented in this paper for the propagation characteristics of a via which connects two semi-infinitely long transmission lines through a hole in a ground plane. The current distribution on the via and a section of transmission line became solved under the thin wire approximation by the moment method and the scattering parameters are extracted by the matrix pencil method. Numerical results were included to investigate the frequency dependent propagation characteristics for via structures with various geometrical parameters, e.g. the via height, wire diameter, and via hole radius. The radiation loss was shown from a comparison with the quasi-static model to become important if the via height is larger than one tenth of a wavelength. The radiation mechanism could be mainly attributed towards the associated wire antenna structure and, at rather high frequencies, towards the associated grounded via structure     

Electromagnetic modes in conical transmission lines withapplication to the linearly tapered slot antenna

A transmission line analysis of the bow-tie antenna and the linearly tapered slot antenna (LTSA) is presented. These structures belong to the class of conical transmission lines defined here in terms of conical coordinates. A complete set of solutions of the Helmholtz equation is obtained exhibiting TE and TM modes. Modal fields are expressed by Lame (1837) and Bessel-Schelkunoff functions. TE and TM eigenmode analysis is particularized to the bow-tie structure. Bow-tie antenna and LTSA are shown to be dual conical transmission lines by the image method and Babinet's principle. The modes of LTSA are calculated on the basis of the results obtained for the bow-tie structure. The radiation pattern of the LTSA is computed as the integral of a closed-form expression of the dyadic Green's function weighted by the modal electric field distribution over the slot aperture. The obtained dominant mode radiation patterns are validated by measurements from the literature. The radiation patterns of the first two-order modes are calculated and compared     

Analysis of a slot microstrip antenna

The slot microstrip antenna is used as a folded slot dipole symmetrically fed across a gap by means of a strip line. A theoretical model equivalent to several lossy transmission lines had been described previously to explain the bandwidth and the radiation admittance. The theory is improved when coupling between the two equivalent radiating lines of every slot is taken into account, and explains a fourth resonance near the third one, which had been measured on several models. Theoretical results and experiments are in good agreement. They are radiation admittance in a wide frequency band, current distribution along each slot and radiation patterns.     

IEEE 802.11协议中分布式协调机制的性能模型

IEEE 802.11采用异步传输方式作为媒体层的主要技术,而基于载波检测碰撞避免的分布式接入机制则是其最大的特点.关于分布式接入机制的研究,目前已经有了许多的模型,但是,大部分的模型都是研究终端所产生的数据包是固定长度,很少有模型来研究终端数据包是可变长度的情况.这种情况下的难点就是不易求得碰撞发生时信道所消耗的时间长度.本文则研究在终端数据包长度的分布函数为f(x)下协议的吞吐量和延迟性能模型.首先本文将原标准协议的退避算法看成是有固定大小的竞争窗口,用以求得站点的发送概率;然后,分析信道的工作状态,给出了性能模型,重点在求解碰撞消耗的信道时间,在文章的最后,我们通过仿真试验来验证了模型的正确性.