板状天线作机械倾斜的垂直方向性函数的计算及分析

板状天线作机械下倾的目的是为了实现主波束的下倾，形成伞型场，同时也克服了直立式天线零幅射点多的弱点，本文通过建立机械倾斜式天线的垂直方向性函数来讨论它的一些特点。     

天线方向性图绘制软件的开发

本文介绍了笔者开发的天线方向性图绘制软件。该软件完全模仿学生手绘方向性图的过程,学生可以藉此完成简单、重复和耗时的函数值计算过程,更重要的是完成了学生无法画出的立体方向性图。该软件具有较好的通用性和参与性,学生藉此能够亲自实践整个方向性图的绘制过程,且不需要花费太多时间。     

基于机械倾斜方式的过顶跟踪算法

首先推导了卫星过顶时盲区的计算公式,然后给出了实施机械倾斜过顶跟踪时,基于TILT A'-E'型三轴座架的倾斜范围的选取方法和倾斜轴方向的确定途径。经实际工程验证,这种倾斜范围的选取方法和倾斜轴方向的确定途径是合理、可行的。     

基于DPCA与NN联合处理的智能天线方向性补偿

针对星载智能天线载体不可避免的振动、形变等因素带来的阵列方向性恶化问题,提出结合神经网络自学习算法的阵列系统动态方向性补偿方案.在子空间特征分析的基础上,研究了BP网络对动态偏角方向性补偿问题的映射能力,推导了神经网络方法结合DPCA参数调控的方向性补偿算法.仿真实验结果证明了上述方法的可行性及正确性.     

气溶胶垂直分布对大气层顶反射函数的影响

在大气-海洋系统中如果不考虑气溶胶垂直分布将给离水反射率的反演带来一定的误差,进而影响水色遥感的精度。利用辐射传输模型模拟了气溶胶垂直分布对大气层顶(TOA)反射函数的影响,结果表明:当不能正确考虑气溶胶垂直分布特性时,TOA反射函数R将会产生10%甚至30%的误差;气溶胶吸收性越强、光学厚度越大,所产生的R的相对误差(△R)也就越大;气溶胶吸收性越强,△R受相对方位角的影响也越大;当气溶胶具有强吸收性时,其分布高度越低,R越大。     

绝热式方向性耦合器修正型汉明权重函数之适当波导长度与结构影响

研究绝热式方向性偶合器修正型汉明权重函数之适当波导长度与结构影响.传统的光方向耦合器之理论是由绝热条件下所获得之结果,因此在波导耦合长度不夠长时则变得可疑,有鑑于此需要依靠光束模拟软件.文中主要的指标为修正型汉明权重函数之低串扰、宽频宽和较短的耦合器长度.最后由结果得知我们所提出使用的修正型汉明权重函数在此架构下能获得较佳的设计结果.     

代价函数权值可变的速度自适应的异构无线网络垂直切换算法

利用移动车载终端的测速功能,针对移动WiMAX网络支持高速移动的特点,本文提出了一种在异构无线网络中的基于车载终端的代价函数权值可变的速度自适应垂直切换算法.该算法使用速度自适应策略克服了网络发现阶段采用测量网络的接收信号强度这种固定且单一的网络发现方式带来的缺点,提高了候选网络集更新速度,改进了高速移动用户网络发现的...     

一种改进的分布式天线系统帧同步度量函数与算法

传统分布式多输入多输出正交频分复用(Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing,MIMO-OFDM)系统定时同步算法中,帧同步算法都是通过直接选取经验值作为阈值进行帧头捕获,而当发射天线数改变时同步度量值变化较大,这将大大增加漏捕获和误捕获的概率.针对这一问题,通过对传统度量函数进行统计特性分析,提出一种修正的定时同步度量函数,推导了其统计特性,并且基于‘3σ'阈值选取准则,形成一种新的基于计算阈值的帧同步(Frame Synchronization Algorithm based on Computed Threshold,CTFS)算法.进行了大量的仿真实验,在不同MIMO发射天线数目下,比较了提出的CTFS帧同步算法与传统的不等周期同步(Unequal Period Synchronization Pattern,UPSP)方案和正交变周期同步(Orthogonal Variable Period Synchronization Pattern,OVPSP)方案的帧同步性能,实验证明相较传统算法,提出的算法大大提高了同步度量值及同步性能的鲁棒性,解决了传统同步度量函数在发射天线变化时出现的问题.     

使用函数式语言与命令式语言混合开发EDA程序的一次探索

相较于命令式语言,函数式语言有两个明显的优点：安全性好、开发周期短.但一般而言,函数式语言的代码性能不够好,妨碍了它的推广和实践应用,尤其是在性能要求很高的领域.基于上述问题进行了一次函数式语言和命令式语言混合编程的探索,试图在同一个项目中结合两类编程语言混合编程,一方面用函数式语言OCaml快速编写复杂度较高的算法核心代码;另一方面,用C语言编写难度不大但是对性能影响比较大的代码,通过这种混合编程方式在较短的时间内可以实现一个结构比较复杂但在性能上接近C语言编写的同类代码的软件.选用海量图形数据的高速区域化查询这一案例,该EDA问题对运算效率有较高的要求,所以在数据结构上选择四叉树结构来实现区域查询,因此是一个比较有代表性的使用高效数据结构来满足性能要求的问题.实验结果表明,OCaml和C的混合编程能将核心算法的研发周期明显缩短,同时性能与C语言编写的同类型的代码相仿,这也就说明了函数式语言和命令式语言的混合编程可以成为EDA软件开发的一个可行的方案.     

Evaluation of directivity for planar antenna arrays

In this paper, the directivity, including phase shift factors, for several types of uniformly excited planar arrays is obtained. Four types of dipole arrays are considered: arrays of collinear short dipoles, and of parallel short dipoles; and broadside and end-fire arrays of crosses of short dipoles. Curves of directivity versus inter-element spacing and scan angle for planar arrays with these element power patterns are presented     

口径天线方向性系数和增益的快速估算方法

导出了用天线方向图的半功率波束宽度快速计算口径天线方向性系数和增益的简单表达式，分析讨论了这些公式的应用范围。最后，给出了卫星通信天线的增益测量实例，实验结果表明：用半功率波束宽度快速计算的天线增益与其它方法测量的天线增益吻合很好，从而证明了这种方法的正确性。     

一种小型平面超宽带天线的设计与研究

提出了一种新颖的小型平面超宽带(UWB)天线.该天线由微带槽天线的基本结构变形而来,为获得超宽带频率特性,设计时馈电微带线采用了渐变结构的叉形调谐支节,金属底板的开槽设计成对称多边形.首先通过数值计算来获得最佳的天线几何尺寸,并制作了实际的样品.对天线的反射特性、方向图以及增益都进行了测试,然后利用时域有限差分(FDTD)方法计算了天线收发脉冲信号的保真度.研究结果显示该天线具有良好的超宽带特性.     

Novel analysis and design approaches of the planar antenna arrays

New approaches for the determination of the radiation characteristics of planar arrays are proposed. Conventionally, the best compromise directivity-side lobes level is achieved using Dolf-Chebyshev amplitude distribution. However, classical distribution forms present disadvantages in calculation time, possibility in analyzing larger arrays and the array factor is only optimum in the two principle planes. To overcome these problems, the excitation amplitudes are written under the modal form. The obtained radiated fields compared with measurement results validate the technique. It is also shown that square arrays provide improved performances from point of view of directivity compared to those of rectangular arrays with comparable size. However, above specific array size, the directivity saturates. For this, another modification of the array factor of Chebyshev square array is proposed. The modification preserves the radiation pattern configuration (same number of null radiation directions and sidelobes) and improves both directivity and side lobe levels. Analytical expressions of the array factor, the directivity, maximum half-power beamwidth, and the maximum spacing between elements have been derived. It has been shown that the use of this new technique results in an improved directivity with respect to the classical Chebyshev for a square arrays identical in size, element spacing, direction of the main lobe and side lobes level.     

Design and analysis of an R-shaped dual-band planar inverted-F antenna for vehicular applications

A dual-band R-shaped planar inverted-F antenna is proposed for vehicular application. Utilization of this unique geometry dual-frequency operation is achieved with a single feed. The proposed antenna operates in the 225- and 450-MHz bands. Input impedance and return loss data as function of various antenna parameters are presented, which show that parameters can be adjusted in order to obtain optimum tuning. Radiation pattern data for the antenna mounted on the roof of two types of vehicles are given. The pattern in the low-frequency band is essentially omnidirectional while that in the high-frequency band is directional and normal to the antenna surface. With proper scaling, this antenna may be suitable for dual-band GSM 900/1800-MHz phone applications.     

Finite-difference time-domain analysis of a stacked dual-frequencymicrostrip planar inverted-F antenna for mobile telephone handsets

We describe a stacked, dual-frequency microstrip planar inverted-F antenna (DF-PIFA) for mobile telephone handsets that can concurrently work in two frequency-bands, viz., those associated with the GSM and DCS 1800 systems operating at 0.9 GHz and 1.8 GHz, respectively. The proposed microstrip DF-PIFA is fed by a coaxial line, as opposed to two separated feed lines used in the conventional design. The design is carried out in a systematic manner and involves two steps. We begin with an initial configuration of the PIFA that is based on a standard design for a microstrip patch antenna fed by a coaxial line and is derived from an empirical approximation in conjunction with a transmission line model. Next, we employ a computer-aided design (CAD) tool, based on the nonuniform finite-difference time-domain (NU-FDTD) Maxwell solver, to optimize the performance characteristics of the DF-PIFA, including the return loss, the matching of the input impedance, and the far-field radiation patterns     

Design and development of planar antenna array for mimo application

Wireless Networks - Multi-Input Multi-Output (MIMO) is the need for recent communication system for the enhancement of channel capacity. While the number of antenna array elements increased, the...     

电小甚低频发射天线的地损耗电阻计算与分析

针对电小甚低频发射天线辐射电阻小,地损耗影响天线辐射效率的问题,文中研究了基于解析法计算分区域均匀辐射状地网区内磁场损耗电阻、电场损耗电阻和地网区外磁场损耗电阻、电场损耗电阻的方法,根据该方法可实现对分区域均匀辐射状地网的损耗电阻计算.计算结果表明,电小甚低频发射天线的磁场损耗电阻是地损耗的主要部分;此外,在地网总长度和地网敷设区域半径不变的条件下,均匀辐射状地网并不是甚低频天线的地网敷设最佳模式.基于上述结果,提出通过分区域敷设均匀辐射状地网的方法来降低地损耗电阻,为进一步提高电小天线的辐射效率提供了一种新的途径,具有一定的理论和工程实践指导意义.     

Meta-heuristic optimization algorithms for comparative analysis of uniform and non-uniform elliptical array antenna for enhanced gain

In this article, the synthesis of a non-uniform elliptical array antenna (EAA) is presented applying three relatively new, well-performing meta-heuristic optimization algorithms; quantum particle swarm optimization (QPSO), symbiotic organism search (SOS), and moth fly optimization (MFO) algorithms. The design objective allows simultaneous minimization of side lobes and maximization of gain by finding the best optimal combination of angular locuses of the antennas in the array structure. The proposed technique is efficient enough to resolve the underlying multi-objective problems at two principle planes of radiation and adaptable enough to the effective implementation of additional design constraints which make this design suitable for practical high-frequency applications as well as long-distance communication. The iterative accomplishment of the three algorithms is compared depending on the radiation parameters as well as statistical parameters. The outcomes are validated by performing a t test on the obtained data sets.     

Time-domain analytic and numeric analysis of vertical dipoles infront of a dielectric planar interface

Potentials excited by impulsive vertical electric and magnetic dipoles in a geometry of two dielectric media with a planar interface are studied both analytically and numerically. Closed-form expressions for the Hertzian potential are derived in cases when the observation point is on the axis of the dipole or when both the dipole and the observation point are located at the interface. Numerical results are given for more general observation points