曲面偶极子方向性系数的优化

本文在矩最法计算曲偶极子特性数据的基础上对方向性系数进行了优化，得到了曲面偶极子方向性系数的最大值。     

对板状单极加载天线的研究

本文从经典偶极子出发分析了其不能实现宽带的原因。通常为实现宽带可把偶极子的两臂变形为三角形，但这又会带来如横向尺寸太大等一系列问题，因此这里对三角形偶极子的馈电处进行了改进，以便于宽带匹配，并对由改进后的偶极子一臂构成的板状单极子的阻抗特性进行了讨论；接着以解析法讨论了该板状单极子的方向性；最后通过一个设计实例进行了验证。     

太赫兹时域频谱仪用宽带光导天线的研究

采用大型电磁计算软件CST对一种现有的偶极子型光电导天线的方向性进行仿真计算。结果表明,这种偶极子型光电导天线或最大辐射方向随着频率的变化而发生显著变化,方向性比较差,造成其在应用于太赫兹时域频谱仪时效率低下,且对环境存在电磁污染的问题。本文的研究方法可以用于研究新的光电导天线,从而改进太赫兹时域频谱仪用光电导天线的性能。     

一种新的无源偶极子天线辐射效率测量方法

提出一种无源超高频(UHF)射频偶极子标签天线在自由空间中辐射效率的测量方法并通过仿真和实验对其验证。辐射效率是标签天线的一个重要性能参数,通过测量标签天线的3个基本参数,即方向性系数、实际增益和功率传输系数得出结果,最后对比仿真与实测结果,两者取得良好的一致性,验证了该方法是可靠的。该方法的一个主要优点是可以在实际应用环境中对标签天线辐射效率进行测量,具有广阔的潜力。     

双蝶形金属纳米光天线的远场特性研究

为了提高对远场方向性调控的灵活性,提出双蝶形银纳米光天线,基于时域有限差分的方法研究了天线不同结构与尺寸的变化对远场方向性产生的影响。研究发现,由于局域表面等离激元的存在,偶极子源垂直放置于双蝶形银结构下表面一定距离时,远场方向图出现明显的旁瓣。天线长度的增加是方向图出现旁瓣的关键因素。天线臂之间夹缝的减小,使远场方向图中旁瓣增大,同时主瓣增益增大。天线厚度的增加使远场方向图出现旁瓣,主瓣增益先增大后减小。结果表明,双蝶形银纳米光天线能够改变与其相耦合的偶极子源的辐射方向性。     

圆柱面上的轴向偶极子阵的低副瓣方向图优化综合

本文利用新的非线性最优化方法讨论圆柱面上的轴向偶极子阵的低副瓣方向图优化综合问题，利用阵列的单元可实现增益方向图，我们把阵列综合问题表述为一个约束非线性规划问题，采用新直接法求解该问题即可得出一组使阵列的总方向图满足副瓣指标要求，同时具有尽可能高的方向性系数的激励系数，如果阵列的总方向图不能达到副瓣指标，则可得出一组使阵列方向图在可达到的副瓣方向图综合设计的模拟计算结果。     

一种超方向性阵列天线综合方法

以往的阵列综合方法不能在获得高的方向性系数的同时保证外部噪声占优,不能用于超方向性阵列综合 .本文提出了一种新的阵列综合方法,该方法适用于任意阵列形式,以最大化阵列方向性系数为目标,通过对阵列效率的约束保证了外部噪声占优的条件,并通过迭代控制了方向图的旁瓣,实现了阵列效率和旁瓣约束下的方向性系数最优化,很好地满足了超方向性阵列综合的要求 .对多种阵列的综合结果表明了这种方法的有效性和灵活性 .     

高能原电子下金属曲面二次电子发射的理论研究

从半经典定理出发,根据金属二次电子发射系数与入射角度的近似关系,分析了曲面的二次电子发射,推导出高能原电子入射情况下,两种常规金属曲面(圆柱曲面和球冠曲面)的二次电子发射系数,进一步得到任意曲面二次电子发射系数的求解思路,分析并讨论了结果.     

太赫兹光导天线阵列功率空间合成规律研究

采用天线瞬态辐射理论和数值仿真方法,分别研究了阵元个数、阵元间距、激励延迟等物理参量对光导天线阵列功率空间合成效率的影响。通过深入分析和对比文献报道的实验数据,发现在不考虑非线性饱和效应和电磁屏蔽的条件下,对于轴向排列的偶极子光导阵列,导致功率合成效率不高的重要原因主要源自:偶极子的方向性辐射、电磁能量空间耗散和非同步光激励。     

交叉极化及副瓣约束的任意阵列最优方向性综合

本文根据给定的期望极化方向,定义了扫描波束的期望主极化和交叉极化方向,并进一步给出了主极化方向性系数的定义,它可以更为准确的表征天线集中辐射主极化分量的程度.在没有副瓣约束和交叉极化约束的条件下,给出了任意阵列主极化方向性系数最优解的解析表达式.并且,在含副瓣约束、零陷约束以及交叉极化约束的条件下,我们发展了一种基于凸优化的高效数值综合方法,实现多约束条件下的主极化方向性系数的优化.数值阵列综合结果表明了本文所提出的最优主极化方向性系数解析解的正确性,以及这种可以综合考虑副瓣约束、零陷约束和交叉极化约束的数值方向性优化方法的有效性.     

DIRECTIVITY OPTIMIZATION OF CURVED SURFACE DIPOLE ANTENNAS

Based on the calculation of the characteristic parameters by moment method, the curved surface dipoles are optimized by an optimization method, the maximum directivities of some V-curved and Gauss-curved surface dipoles are given.     

振子阵列天线的雷达截面积

本文用矩量法,对大型平面阵列和圆阵柱阵列天线在不同加载情况下的散射进行了研究。在考虑振子互耦情况下,计算出振子上的电流分布,并得到阵列的雷达截面积(RCS)。实验结果表明,理论值与实验值两者基本趋势一致。文中采用的平面阵加截和共形曲面阵技术,可大幅度地缩减振子阵列天线的RCS,具有实际的工程意义。     

Absorption efficiency of receiving antennas

A receiving antenna with a matched load will always scatter some power. This paper sets an upper and a lower bound on the absorption efficiency (absorbed power over sum of absorbed and scattered powers), which lies between 0 and 100% depending on the directivities of the antenna and scatter patterns. It can approach 100% as closely as desired, although in practice this may not be an attractive solution. An example with a small endfire array of dipoles shows an efficiency of 93%. Several examples of small conical horn antennas are also given, and they all have absorption efficiencies less than 50%.     

Beam scattering by a right-angled impedance wedge

Following earlier developments, a uniform asymptotic solution for two-dimensional high frequency scattering by a right-angled impedance wedge is presented. The wedge supports surface waves on both faces and numerical examples show the relative significance of these surface waves for different surface parameters, source directivities and positions of source and receiver. Surface parameters extracted from experimental data for buildings are used to show that for near grazing incidence surface waves can have a very significant effect along the direction of specular reflection even in the far field. These results should be important in urban propagation modeling.     

Surface wave in multilayer dielectric structures excited by varioustypes of Hertzian dipoles

The surface wave excitations of deferent types of Hertzian dipoles in multilayer dielectric structures are investigated. General expressions are derived for analysis of the surface wave power produced by the dipoles in the structure. Numerical results are given for some special cases, which are in good agreement with earlier work reported by other researchers     

Electromagnetic surface waves: New formulas and applications

Relatively simple and accurate formulas are now available for the complete electromagnetic field generated by vertical and horizontal dipoles located on or near the boundary between two electrically different half-spaces such as air and water or rock and sea water. The principal part of the field is an outward-traveling lateral wave with useful properties. The formulas are given and their application to a variety of problems reviewed briefly. These include: radio communication over the surface of the earth or sea, the wave antenna, communication with submarines using vertical dipoles in air and horizontal dipoles in the sea, the location of buried objects using horizontal dipoles on the surface of the earth, and the measurement of the conductivity of the sea floor.     

The West Ford payload

The problem of establishing an orbiting dipole belt of particular dimensions imposes constraints on the method used to dispense the dipoles. The technique chosen is that of binding the dipoles together in a subliming matrix material. The dipoles are assembled to form a right circular cylinder which is rotated about its axis of circular symmetry. Incident solar energy in the vacuum in orbit results in rapid sublimation of the matrix material. The dipoles are then released from the surface of the rotating cylinder. This technique of dispensing dipoles, the method of handling fine wire to produce properly packaged dipoles and the procedure for impregnating the dipole packages with the subliming binder material are described. The actual performance of the dispenser device in orbit and the results of ground tests of the dispensing technique before and after launch are discussed.     

Mutual impedance computation between printed dipoles

The mutual impedance between microstrip dipoles printed on a grounded substrate is computed. Results for the microstrip dipoles in broadside, collinear, and echelon arrangements are presented. The significance of surface waves to mutual coupling is discussed.     

Channel Alternation and Rotation for Trisectorized Cellular Systems

Conventional trisectored cellular systems have not taken full advantages of antenna directivities to enhance frequency reuse efficiency. A novel Channel Alternation and Rotation (CAR) scheme is proposed to coordinate channel assignments with antenna directivities. CAR employs a multi-interval cell-reuse layout. Each cell type is allocated extra channel set(s) to provide network designers the flexibility to assign channels avoiding nearest front lobe interference to enhance the carrier to interference ratio (C/I). CAR allows deployment of smaller and non-integer reuse factors based on C/I requirements, thus increasing channel capacity. Since current base station equipment is utilized, no additional costs are introduced.     

Suppression of parasitic currents on feed lines of colinear dual antenna systems

Investigations are reported of an antenna system consisting of a pair of colinear dipoles with a feed line "isolator section" which provides independent operation of the dipoles over an octave frequency range. The isolator section acts as a band elimination filter for the parasitic currents induced on the outer surface of the transmission line of the upper dipole. Suppression of these currents eliminates distortion of the antenna radiation patterns and significantly reduces coupling between the dipoles. Over the 200-400-MHz range, an interdipole isolation greater than 35 dB has been achieved between the colinear dipoles separated by 1.5 m.