T型甚低频多调谐发射天线电容与电感研究

甚低频天线理论认为,采用多调谐方式,T型甚低频多调谐天线可以基本按比例增加天线电容,在实际工程中常用五组或六组天线.本文利用甚低频天线输入电抗的实测值,计算了在不同频率下天线所呈现的等效电容和等效电感,研究了T型甚低频发射天线的等效电容、电感、功率容量与天线组数及频率之间的关系.研究结果表明T型甚低频多调谐天线的组数过...     

甚低频发信系统工作性能仿真研究

针对甚低频发信系统工作性能的研究,建立了甚低频发信系统仿真模型,利用模型对甚低频电子管发信系统工作在假负载模式、天线模式、固定调谐方式及动态调谐方式分别进行了仿真计算,分析了不同方式、不同载频及不同码元速率下的系统传输性能。计算结果表明甚低频发射天线动态调谐系统具有比固定调谐方式传输效率高,系统允许的信息传输速率可得到大幅提高。     

机载隐蔽式短波天线设计

机载天线是飞机导航、通信等系统的重要组件;实现远距离通信主要依靠机载短波天线。新型复合材料的使用以及飞机尺寸的增大,是国际飞机发展的潮流。针对这一问题,该文利用电小天线及传输线相关理论设计一种新型大型飞机机载隐蔽式短波天线,设计过程中使用电磁仿真软件Ansoft HFSS建模计算天线输入阻抗及方向图并优化天线尺寸;在此基础上,制作缩比模型并在微波暗室中对其进行实测,所得数据与仿真结果相符。除此之外,对天线的阻抗匹配及效率进行分析并给出计算结果。计算及测试结果表明,此天线可与天线调谐系统(例如KHF950)良好调谐,方向图为水平全向,符合应用要求,可用于整个机身或仅垂尾为复合材料的大型飞机。     

液晶嵌入电调谐频率可重构双频天线设计

为了提高可重构天线的频率调谐范围,设计了一种液晶嵌入电调谐频率可重构双频天线.对液晶嵌入取向层处理方法、封装方法、电调谐介电特性测试原理与方法进行了研究.采用三层堆叠方式设计了液晶天线结构,在馈电微带下方填充液晶,利用液晶材料的电控特性改变天线的电特性,从而实现双频可调谐.分析了液晶天线寄生枝节尺寸、矩形微带馈线矩形槽...     

天线共用器

本文主要是对天线共用器的两种构成方式（可调谐带滤波器构成天线共用器和用环行双工器构成天线共用器）进行介绍和探讨。     

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.     

介质杆天线的时域特性分析

超宽带技术在通信、雷达等众多领域获得广泛应用，时域天线是其关键技术。对介质杆天线用作时域天线的可行性进行了分析，并给出选择介质杆参数的依据。同时还使用FD-TD(时域有限差分法)数值计算方法分析了在超宽带情况下介质杆的直径、激励方式及终端渐变方式对天线的传播特性及辐射特性的影响。分析表明这种天线适宜用作时域天线。     

舰载多波束测向天线系统的热设计

介绍舰载多波束测向天线系统的热设计问题,根据海用环境条件和具体装载要求以及天线系统本身的结构特点,选择散热方式和途径,提出一种新颖的散热结构形式,并对其进行了详细的热分析计算。经过实验室联试,散热效果是令人满意的。     

一种顶部加载型Sierpinski垫片天线的分析

将分形几何应用于天线设计可以产生具有多频段或小型化特征的分形天线。传统的多频段分形天线Sierpinski垫片天线由于是有限次迭代生成的,它存在截取效应低端谐振频率比值几乎是其几何相似性因子的两倍,从而限制了其实际应用。本文针对一种小型化的加载型Sierpinski垫片天线进行了有效的研究,证实了加载对降低天线高端谐振频率的有效性,同时分析了结构参数对其工作频段的影响并提出了增大天线张角的方式以进一步小型化天线。     

RFID系统中的天线调谐设计研究

本文论述了天线调谐在AS3992的RFID系统中的应用,并进行了相关调谐算法的研究,得出了一套有效的调谐算法.该算法根据实时所用的不同外接天线,测得天线端的反射功率,由主控51芯片对匹配电路进行动态调节,最终获得最佳的匹配参数,实现无反射传播,实现了差异化外接天线不影响RFID系统性能的目的.应用该动态调谐算法,RFID系统的稳定盘存距离能达到9m.     

Antenna applications of superconductors

The applicability of superconductors to antennas is examined. Potential implementations that are examined are superdirective arrays; electrically small antennas; tuning and matching of these two; high-gain millimeter-wavelength arrays; and kinetic inductance slow wave structures for array phasers and travelling wave array feeds. It is thought that superdirective arrays and small antennas will not benefit directly, but their tuning/matching networks will undergo major improvements. Miniaturization of antennas will not be aided, but much higher gain millimeter-wave arrays will be realizable. Kinetic inductance slow-wave lines appear advantageous for improved array phasers and time delay, as well as for traveling-wave array feeds     

Multiple-tuned VLF antennas

Different approaches to feeding two multiple-tuned VLF antennas with regard to antenna performance and tuning are compared. Both antennas may be fed separately, or only one may be fed and the other grounded through a previously tuned coil. The antennas may either be connected or separated at their capacitive ends. The maximum bandwidth-efficiency product of all these arrangements is the same. Connected antenna systems achieve this maximum for all adjustments with in-phase base currents, and the most favorable tuning depends on the efficiency desired. If only one antenna is fed, the tuning procedure is quite simple, because only current magnitudes have to be adjusted. Retuning of the coils in the nonfed upleads is not necessary if changes are small compared with the magnitude of the antennas' coupling reactances. Connected element systems are particularly stable. These properties can be transferred to other multiple-tuned antenna systems of electrically short elements with top capacitances     

Adjustable frequency dielectric resonator antenna

An easy method of tuning the resonant frequency of cylindrical and ring dielectric resonator (DR) antennas using different diameters of conducting plates is presented. This technique can tune a DR antenna to operate at the design frequency without changing antenna performance. The maximum frequency tuning range can reach up to 300-500 MHz     

Physical principles of plasma antenna operation

Basic principles of operation of plasma antennas based on volume and surface plasma waves are presented. It is demonstrated that the efficiency of plasma antennas does not yield to that of metal antennas and that the controllability (frequency tuning for reception and transmission) and radar invisibility (a small radar cross section) are significantly higher. Plasma antennas of two types are considered: dipole antennas operating based on the surface plasma wave, and slotted waveguide antennas operating based on the volume plasma wave.     

A Frequency Tuning Method for a Planar Inverted-F Antenna

A novel method is presented for electrically tuning the frequency of a planar inverted-F antenna (PIFA). A tuning circuit, comprising an RF switch and discrete passive components, has been completely integrated into the antenna element, which is thus free of dc wires. The proposed tuning method has been demonstrated with a dual-band PIFA capable of operating in four frequency bands. The antenna covers the GSM850, GSM900, GSM1800, PCS1900 and UMTS frequency ranges with over 40% total efficiency. The impact of the tuning circuit on the antenna's efficiency and radiation pattern have been experimentally studied through comparison with the performance of a reference antenna not incorporating the tuning circuit. The proposed frequency tuning concept can be extended to more complex PIFA structures as well as other types of antennas to give enhanced electrical performance.     

A planar Van Atta array reflector with retrodirectivity in bothE-plane and H-plane

A planar antenna array reflector with retrodirectivity in both the E-plane and the H-plane is analyzed and demonstrated at X band. The reflector consists of six pairs of slot-coupled patch antennas arranged using the Van Atta approach. The total reflected field from the reflector is separated into three primary components; that is, the reradiation field from the patch antennas (RFPA), the scattering field from the patch antennas (SPPA), and the scattering field from the ground plane (SFGP). The first two components are calculated by using the method of moments together with a mixed potential integral equation and the last one is by the physical optics (PO) method combined with the method of equivalent currents (MEC). By tuning the microstrip-line lengths, the total reflected field contributed by the three components is designed to possess a broad-beamed pattern in both the E-plane and the H-plane. The measured patterns show good agreement with the designed ones     

Optimization and comparison of compact printed antennas by a set of performance indexes

The problem of optimization of the parameters of compact printed antennas for a set of performance indexes in order to determine their potential performance characteristics is considered. Half-wave, quarter-wave, folded half-wave and folded quarter-wave radiators with linear polarization are studied. Electromagnetic simulation is used to obtain the sets of feasible solutions for these antennas in the space of the following performance indexes: (Q factor, overall dimensions), (Q factor, volume), and (Q factor, radiator area). The unconditional preference criterion is used to find the sets of Pareto-effective solutions. The sets of parameters of effective antennas are obtained. The results of comparison between different designs of compact printed antennas in the set of performance indexes are presented.     

Ferrite-loaded cavity-backed antennas including nonuniform and nonlinear magnetization effects

A method of analyzing both the electromagnetic and the magnetostatic phenomena involved in ferrite-loaded cavity-backed antennas is presented. The high-frequency modeling of the antenna is based on a hybrid of the finite element method (FEM) with the method of moments (MoM). The (magnetostatic) demagnetizing process of the finite ferrite loadings is modeled with the use of a nonlinear static FEM. The results of the magnetostatic analysis are used to compute the internal field of the ferrite samples. Through the use of an appropriate ferrite permeability tensor, the nonuniform internal bias field is incorporated into the high-frequency FEM/MoM analysis. The input impedance characteristics of two different ultrahigh-frequency (UHF) antennas are presented using different ferrite models. Results for the tuning range and sensitivity are presented for different bias directions. The numerical results are also compared with experimental data.     

CPW-fed stacked microstrip antennas

This paper presents a systematic parameter study of aperture-coupled stacked patch antennas fed by coplanar waveguide. These antennas are to be used at millimeter-wave frequencies in the 30-GHz range. The influence of the most important design parameters, such as patch dimensions, aperture dimensions, and substrate thicknesses, was studied extensively. It has been found that these antennas can easily be impedance-matched by tuning the dimensions of the excitation slot and adding a small tuning stub. In this way, an antenna element with a -10 dB impedance bandwidth of 36.8% has been designed. Furthermore, the results of this parameter study have allowed to formulate some general guidelines concerning the design of this type of antenna element.     

Study of printed elliptical/circular slot antennas for ultrawideband applications

Two novel designs of planar elliptical slot antennas are presented. Printed on a dielectric substrate and fed by either microstrip line or coplanar waveguide with U-shaped tuning stub, the elliptical/circular slots have been demonstrated to exhibit an ultrawideband characteristic. The performances and characteristics of the proposed antennas are investigated both numerically and experimentally. Based on these analyses, an empirical formula is introduced to approximately determine the lower edge of the -10 dB operating bandwidth. It is also shown that these antennas are nearly omnidirectional over a majority fraction of the bandwidth.