用FDTD法计算架设在有损地面上高频段单极天线辐射特性

在高频波段(2~30MHz),由于天线架设在环境复杂中,计算其辐射特性和电磁波传播特性非常困难,少有文献对此进行分析.随着高频技术的发展,这一现实问题迫切需要解决.本文用时域有限差分法(Finite Difference Time Domain)对这类问题进行了分析计算.文章计算了架设在有损地面上的单极天线辐射特性,并分析了架设海岸边的单极天线辐射的电磁波经过一段有损陆地后,其远区电磁场随陆地距离的变化特性.在计算中引入了表面阻抗法概念,使计算量和存储空间大为降低.     

地面反射电磁波影响的分析

依据地面电磁波反射的形成原理,探讨了地面对电磁波的反射,对天线架设造成的影响,根据地面反射电磁波的影响,提出短波传播方法,以及天线如何架设,以便在天线及电磁波测量试验中减小测量误差,提高测量精度,达到较好的效果.     

天馈线系统维护与故障分析处理

1发射天线 发射天线的主要作用是把由馈线送来的高频振荡电流转换为高频电磁波的能量,并有效辐射出去。     

导电结构上线天线之间的电磁耦合

天线的架设受到环境结构的限制，特别是在同一导电物体上架设两付甚至多付天线的情况，天线之间的相互耦合成为人们普遍关心的问题,本文应用矩量法与几何绕射理论的混合技术详细计算了两种典型导电物体上的天线之间的耦合度（或隔离度），结果表明混合技术对这类问题的分析计算非常有效。     

电磁波传播与振子天线架设方法

针对某型遥控设备试验过程中,遥控实际作用距离与理论计算存在较大差距的问题,文章通过电磁波传播的路径分析及三次测试验证,并通过对测试结果的分析,提出了降低电磁波传播损耗的天线架设要求。     

介质平面上高频单极天线特性分析

该文用时域有限差分法(Finite Difference Time Domain,FDTD)计算介质平面上单极天线的阻抗特性。用FDTD法计算天线的辐射特性可以使用不同的激励方式,文章比较了采用不同激励方式时,天线的输入阻抗。文章的主要内容是将表面阻抗法用于FDTD中,计算架设在介质平面上单极天线的辐射特性,并用FDTD法计算了介质平面上铺设不同尺寸的导体平面时,天线的阻抗特性。     

高频地波雷达的电离层杂波识别新试验

为了验证电离层杂波干扰的存在及研究其对高频地波雷达性能的影响,武汉大学电波传播实验室在浙江舟山东沙试验基地利用高频地波雷达完成了电离层杂波干扰识别新试验.试验采取改变地波雷达发射天线结构即改变发射天线的波束指向,使得电磁波垂直向上发射,进行电离层垂直探测试验;同时也有部分能量向海洋传播,从而获得海面Bragg散射回波.与此相对应地采用垂直极化的三元八木天线向海洋表面发射电磁波,同时获取海洋回波与电离层杂波.详细介绍了试验过程并对实测结果进行了初步分析,并介绍了新近研制的便携式高频地波雷达OSMAR-S的系统结构及其工作参数.     

电视调频发送天馈线系统

在无线电发送系统中,天线与馈线系统是必不可少的重要组成部分。馈线系统的作用是将发射机输出的高频信号能量馈送给天线,而天线的作用是将高频信号能量转换成电磁波能量,并向空间辐射。     

天线基础知识（十一）

1 传输线的概念及分类 把一种信号能量从信号源传送到远离信号源的负载上，这种传送信号能源的实体结构，通常称为传输线。如，电力传输线就是把发电机发出的大量电能传输到各个使用的负载上。又如，广播和通讯系统中使用的馈线设备就是把发射机末端所产生的高频信号能源，传送给天线设备（负载），然后再由天线转换成电磁波辐射到宇宙空间（或将天线接收下来的高频电磁波能量传送到接收机）。随着科学事业不断的飞速发展，对传输线的应用也越来越广，对传输线的制作种类也越来越多、越来越先进，目前，传输线大体上可分为如下几种：     

利用辛几何理论求解电磁波在非均匀媒质中的传播

提出了一种基于辛几何的高频近似的新方法，并用此方法求解了电磁波在一非均匀媒质中的传播问题。通过辛空间上的坐标变换，使电磁波传播中的焦散问题转化为非焦散的问题，并结合几何光学的方法，求得了包括焦散区在内的高频近似解。解决了几何光学法无法在焦散区求解的问题，还可以推广到二维及三维的情况。     

A Simple Ultrawideband Planar Rectangular Printed Antenna With Band Dispensation

A compact planar ultrawideband (UWB) antenna with band notched characteristics is presented. Modification in the shape of radiation element and ground plane with two symmetrical bevel slots on the lower edge of the radiation element and on the upper edge of the ground plane makes the antenna different from the rectangular printed monopole. These slots improve the input impedance bandwidth and the high frequency radiation characteristics. With this design, the reflection coefficient is lower than 10 dB in the 3.1–10.6 GHz frequency range and radiation pattern is similar to dipole antenna. With the inclusion of an additional small radiation patch, a frequency-notched antenna is also designed and good out of band performance from 5.0–6.0 GHz can be achieved. Measured results confirm that the antenna is suitable for UWB applications due to its compact size and high performance. Also an approximate empirical expression to calculate the lowest resonant frequency is proposed.      

Design Optimization of UWB Printed Antenna for Omnidirectional Pulse Radiation

The use of ultrawideband technology in many applications implies the use of a suitable radiating structure, especially for pulsed systems. The development of a triangular CPW-fed printed antenna with specific ground plane shape is presented. First the triangular element was optimized to minimize return losses and size of the antenna in the [3.1–10.6] frequency band. The evolution of radiation patterns with frequency was also studied, as changes in phase center position and radiation characteristics alter the integrity of transmitted pulses. Thus the antenna ground plane shape was modified in order to maintain almost constant radiation patterns over the entire bandwidth. Time domain measurement methods were used to characterize the antennas and validate these improvements. The procedure is presented and results are plotted in a 3D format and discussed.      

Printed Planar Monopole Antenna Design for Ultra-Wideband Communications

This paper presents an ultra wideband (UWB) planar printed monopole antenna fed by microstrip line. The antenna configuration contains a beveled ground plane. The beveled partial ground plane improves the impedance bandwidth. The measured frequency response demonstrates that the fabricated antenna exhibits an impedance bandwidth of 7.9 GHz over 3.1 to 11 GHz for VSWR < 2. The proposed antenna has ultra-wideband characteristics with omnidirectional radiation pattern and stable gain. Ultra-wideband performance of the proposed antenna is examined through the simulated surface current distributions. Measured results confirm that the antenna is suitable for UWB applications due to its compact size and high performance characteristics.     

Design of a Planar Ultrawideband Antenna With a New Band-Notch Structure

A novel planar ultrawideband (UWB) antenna with band-notched function. The antenna consists of a radiation patch that has an arc-shaped edge and a partially modified ground plane. The antenna that makes it different from the traditional monopole antenna is the modification in the shape of ground plane, including two bevel slots on the upper edge and two semicircle slots on the bottom edge of the ground plane. These slots improve the input impedance bandwidth and the high frequency radiation performance. With this design, the return loss is lower than 10 dB in 3.1-10.6 GHz frequency range and the radiation pattern is highly similar to the monopole antenna. By embedding a pair of T-shaped stubs inside an elliptical slot cut in the radiation patch, a notch around 5.5 GHz WLAN band is obtained. The average gain is lower than -18 dBi in the stopband, while the patterns and the gains at frequencies other than in the stopband are similar to that of the antenna without the band-notched function.     

一种新型具有双陷波特性的超宽带天线设计

本文提出了一种新型紧凑的具有双陷波特性的印刷超宽带天线。天线采用微带传输线馈电,并通过圆形与矩形 的混合结构辐射单元和带有矩形开槽结构的地板来实现天线的超宽带特性,工作带宽覆盖UWB 频率范围。通过地板上 两个对称的J 形开槽和微带馈线两侧对称添加的线型结构单元来实现双陷波特性,两个陷波频段刚好覆盖了3.5GHz 的 WIMAX 频段标准和5.2/5.8GHz 的WLAN 频段标准。同时,该天线在工作频带范围内具有良好的辐射特性,符合超宽带 通信的使用标准。     

Dual-Band Antenna Array with Reduced Mutual-Coupling for Wearable Wireless Communication Applications

In this paper, dual-band wearable microstrip patch antenna printed on FR4-substrate is designed and fabricated for wearable wireless communications. A star-shaped monopole Ω antenna connected to 50 Ω transmission line, backed by partial ground plane is used. The antenna dimensions are optimized for wideband radiation characteristics. Different types of dielectric substrates are investigated for wideband wearable applications. The proposed antenna printed on jeans textile substrate introduces an impedance matching bandwidth of 7.3 GHz with maximum gain of 5 dBi. The effect of mutual coupling between two parallel patches, two opposite patches and two orthogonal patches on their radiation characteristics are investigated. High isolation is achieved for two orthogonal patches placed away from each other by 0.3λ with a rectangular strip etched between them and cutting in the ground plane. The isolation is below ? 29 dB within the frequency band. The structure achieves impedance matching bandwidth of 1.8 GHz in 1st-band and 4.8 GHz in 2nd-band with maximum gains of 8.5 dBi and 5.3 dBi, respectively. A prototype element is fabricated, measured and the radiation characteristics coincide with the simulated results. The structure is simple, light-weight, and is suitable for WAN applications in the frequency band from 2 GHz to 7 GHz. The effect of human body tissue on the radiation characteristics of the antenna array is investigated. 

     

具有双陷波特性的六边形分形超宽带缝隙天线

提出一款具有双陷波特性的六边形分形超宽带缝隙天线,天线总尺寸为32 mmx16 mmx1.6 mm,采用六边形和三角形迭代嵌套的3阶分形结构作为辐射贴片,并采用缺陷地结构作为接地板,实现了3.0～ 15.26 GHz的超宽带带宽.在馈线两侧引入对称L形开路枝节,并在接地板上刻蚀U形窄缝隙产生了4.71～5.87 GHz...     

Measurement of Radiation from Selected TD-2 Microwave Relay Stations

The optimum frequency band for satellite communication systems is generally agreed to be between 1 and 10 Gc. Frequencies in this band are, however, already allocated and or assigned. One solution to this spectrum occupancy problem is frequency sharing, and one of the systems in this band with which a satellite system might have to coexist is the TD-2 microwave radio relay sstem (3.7-4.2 Gc). This paper presents the measured radiation characteristics of several representative TD-2 transmitting terminals. Both ground and airborne measurements are discussed. It is concluded that, subject to some precautions, back-and side-lobe patterns measured in the horizontal plane on an antenna range with ground effects minimized can be used to predict radiation in the vertical plane from these same antennas placed over actual ground. Such a technique, of course,, presupposes that the antenna of interest has been properly designed to somwhat suppress side and back lobes.     

Mesh antennas for dual polarization

Three mesh antennas, all having an extremely small antenna height of approximately 0.06 wavelength above a ground plane, are presented. First, a mesh antenna excited with a balanced feed is analyzed. It is revealed that the mesh antenna radiates a linearly polarized wave with no cross-polarization component in the principal planes. The radiation mechanism is explained using the current distribution. Second, a mesh antenna excited with an unbalanced feed is analyzed. This antenna shows almost the same radiation characteristics as the mesh antenna with a balanced feed. The frequency bandwidth for a VSWR=2 criterion is evaluated to be approximately 3%. Third, a mesh antenna having two perturbation elements is analyzed. It is found that the antenna acts as a radiation element of circular polarization. The frequency bandwidth for a 3-dB axial ratio criterion is calculated to be approximately 1%. The mesh antennas in the first and second analyses can be used as dual linear polarization elements by appropriately switching the feed. Similarly, the mesh antenna in the third analysis can be used as a dual circular polarization element by switching the feed