A Hybrid Method of Moments?GTD Technique for Computing Electromagnetic Coupling Between Two Monopole Antennas on a Large Cylindrical Surface

The problem of analyzing the electromagnetic interference (EMI) between two electronic systems when their antennas are located on or near large scattering objects is a difficult one. In this paper, a hybrid technique for combining the method of moments with the geometrical theory of diffraction (GTD) is extended to account for the mutual coupling between two monopole antennas on a large circular cylinder by means of curved surface-wave diffraction. The results of this technique are compared to those of an analysis program used by the United States Air Force which predicts electromagnetic coupling between aircraft antennas. The close agreement between the results of these two different analysis techniques serves to validate both computer programs.     

大型面天线CAE分析与电性能计算的集成

研究了CAD/CAE集成建模技术和天线组合结构理论,基于反射面位移场并采用PO法分析天线远区电场,解决了由背架、反射面和中心体组成的组合结构网格自动划分难题,开发了面向大型雷达天线结构的集成分析系统.此系统可辅助结构设计人员对天线结构参数进行修改,对结构形状、分布方式进行调整,对天线加工精度、装配精度提出合理要求.工程案例的应用结果证明了该系统的有效性与准确性.     

Combating sun outage in satellite television distribution systems

Two methods of sun outage avoidance in satellite television transmission are discussed. Each method requires two satellites and dual-beam antennas. The two C-band satellites transmit identical programs at the time when the sun outage period occurs. The separation of the spacecraft is dependent on the dual-feed earth station antenna size. For large television receive-only antennas, the separation must be small; for small antennas, or antennas with large beamwidths, the satellite separation can be large. If the separation is larger than 8° on the geosynchronous arc, only one transmit station is required to transmit program information. Scaling this system for Ku-band use is then considered. It is concluded that in a Ku-band direct-broadcasting system with earth station antenna diameters of 1-m and below, the rise in noise temperature due to sun outage is not significant and can be overcome by a modest amount of system margin, equivalent to that normally provided against rain fades     

多天线无线数据通信系统中多用户分集的研究

研究当接收天线不少于发送天线时多输入多输出(MIMO)系统的多用户分集能力。首先从理论上分析了发送天线个数等于1和2时最大似然接收和迫零接收系统的平均吞吐量和调度增益,以及仿真分析了发送天线个数大于2时系统性能。理论分析和仿真表明：在多用户的MIMO系统中,接收的平均信噪比、用户个数、收发天线个数、接收机的结构等对于多用户分集有很大的影响。当发送天线个数为1时,接收天线较少(1,2,3)和平均信噪比为．10dB时调度增益很大,但调度增益随着天线个数和发送功率增大急剧下降。和最大似然接收相比,迫零接收具有更大的多用户分集增益,因此迫零接收机的吞吐量可以很容易超过最大似然接收机。     

Analysis and measurements of conformal patch array antennas on multilayer circular cylinder

In this paper, we present a method of moments (MoM) program to analyze different configurations of arrays of cylindrical-rectangular patches. The patches can be located inside or on the surface of a multilayer circular-cylindrical structure and can be arbitrarily rotated. The antenna structure is rigorously taken into account by using proper Green's functions, and the array is analyzed by using an element-by-element approach. The elements of the MoM matrix are calculated in the spectral domain, and special attention is given to their numerical treatment when analyzing cylindrical antennas with large radii. A laboratory model is built to test different configurations of patches and to validate calculated results. The agreement between measurements and calculations is very good.     

Dual-frequency patch antennas

Dual-frequency patch antennas may provide an alternative to large-bandwidth planar antennas, in applications in which large bandwidth is really needed for operating at two separate transmit-receive bands. When the two operating frequencies are far apart, a dual-frequency patch structure can be conceived to avoid the use of separate antennas. In this paper, a critical overview of possible solutions for dual-frequency patch antennas is presented, and future perspectives are outlined. Geometries are discussed in particular     

相关信道下MIMO信道容量优化算法的研究

该文研究MIMO系统收发端天线采用均匀线阵且放置空间有限,存在相关衰落时信道容量的优化方法。采用规范化信道模型,分析了信道相关性对平均信道容量和最优信号协方差矩阵的影响,推导了最优协方差矩阵的一阶条件;利用Jensen's不等式确定了信道容量的上界,给出了闭式解,并对相关信道下信号的传输模式进行了讨论。仿真结果表明,采用该优化方法,在各种SNR下,其平均容量接近Jensen's上界;得出信道相关程度对信道平均容量的影响依赖于信噪比的结论。     

An optimization program for linear arrays of parallel wires

This is a composite program suitable for handling certain analysis and optimization problems involving linear arrays of parallel thin-wire antennas     

某型机载平面阵列天线结构设计

机载天线工作环境越来越严酷,对机载天线重量及结构强度要求不断提高,机载天线结构需要进行合理化设计.文章针对某型机载天线的具体要求进行了结构设计,运用三维建模软件对其进行三维建模,再借助有限元分析软件对三维模型进行了随机振动分析.根据有限元分析结果及实测值的比对充分验证了模态分析结果的准确性,同时验证了结构设计的合理性.     

Efficient method for analysis and design of aperture-coupledrectangular microstrip antennas

A method for the analysis and design of rectangular microstrip antennas coupled through a small aperture to a microstrip feed line in a two-layer configuration is described. The technique is numerically efficient, making it suitable for computer-aided design. The analysis takes into account higher order modes excited underneath the patch. Analysis results were implemented in two computer programs: an analysis program and a design program based on optimization techniques. Experimental results are presented to validate this method     

A microwave anechoic chamber for radar-cross section measurement

A microwave anechoic chamber has been developed at the Department of Electrical Engineering, University of Malaya, for monostatic and bistatic radar-cross-section measurements. The structure of the chamber is a quarter-section geodesic dome, with a 12 foot radius, and raised three feet above the floor. An antenna railing system is installed inside the chamber. The antennas can be moved along the rails in the elevation direction, with the microwave beam pointing at the center of the dome where the target is located. This design enables a very large combination of incidence and scattering angles in bistatic measurements. Four transmitting antennas are fixed at different elevation angles next to one of the antenna rails. By using an azimuth-over-elevation positioner as the pedestal for the target, and by positioning the movable antenna along that rail beside those fixed transmitting antennas, monostatic measurements with incidence angles ranging from 0 to 90 degrees can be accomplished. A vector network analyzer is utilized to measure the amplitude and phase of the radar returns. An IEEE-488.2 interface bus is used to control various hardware components, as well as to perform data acquisition. A computer program was written to automate the measurement system. Data are stored in raw format, and processed later with dedicated software, so that different processing methods and parameters can be applied. This paper highlights the design and construction of the microwave anechoic chamber, as well as the measurement-system configuration for scattering-cross-section measurements     

Method of moments enhancement technique for the analysis of Sierpinski pre-fractal antennas

The numerical analysis of highly iterated Sierpinski microstrip patch antennas by the method of moments (MoM) involves many tiny subdomain basis functions, resulting in a very large number of unknowns. The Sierpinski pre-fractal can be defined by an iterated function system (IFS). As a consequence, the geometry has a multilevel structure with many equal subdomains. This property, together with a multilevel matrix decomposition algorithm (MLMDA) implementation in which the MLMDA blocks are equal to the IFS generating shape, is used to reduce the computational cost of the frequency analysis of a Sierpinski based structure.     

FDTD analysis of CPW-fed folded-slot and multiple-slot antennas onthin substrates

Folded slot antennas are attractive for active arrays due to relatively large bandwidth, fabrication simplicity, and ease of integration with devices. Currently, there is little design information for these antennas, especially on thin substrates. The finite-difference time-domain (FDTD) method is applied to the analysis of CPW-fed folded-slot antennas. The paper describes the problems encountered in the analysis, compares the theoretical results and measured data, and provides some design information for folded slots. In addition, it explores the manipulation of input impedance through the use of additional slots, yielding antennas with a broadband 50 Ω input impedance     

Broad-band gap coupled microstrip antenna

A microstrip antenna with large bandwidth is developed using a parasitic technique. Compared to the available wideband antennas, the proposed antenna structure is very compact and gives a less distorted radiation pattern with frequency. An impedance bandwidth eight times that of a conventional patch antenna of the same size is achieved. The concept of coupled microstrip line model is extended for theoretical interpretation of the impedance loci. The experimental procedure and results are described, and a theoretical analysis is presented     

Combined array processing and space-time coding

The information capacity of wireless communication systems may be increased dramatically by employing multiple transmit and receive antennas. The goal of system design is to exploit this capacity in a practical way. An effective approach to increasing data rate over wireless channels is to employ space-time coding techniques appropriate to multiple transmit antennas. These space-time codes introduce temporal and spatial correlation into signals transmitted from different antennas, so as to provide diversity at the receiver, and coding gain over an uncoded system. For large number of transmit antennas and at high bandwidth efficiencies, the receiver may become too complex whenever correlation across transmit antennas is introduced. This paper dramatically reduces encoding and decoding complexity by partitioning antennas at the transmitter into small groups, and using individual space-time codes, called the component codes, to transmit information from each group of antennas. At the receiver, an individual space-time code is decoded by a novel linear processing technique that suppresses signals transmitted by other groups of antennas by treating them as interference. A simple receiver structure is derived that provides diversity and coding gain over uncoded systems. This combination of array processing at the receiver and coding techniques for multiple transmit antennas can provide reliable and very high data rate communication over narrowband wireless channels. A refinement of this basic structure gives rise to a multilayered space-time architecture that both generalizes and improves upon the layered space-time architecture proposed by Foschini (see Bell Labs Tech. J., vol.1, no.2, 1996)     

Mobile antenna gain in the multipath environment at 900 MHz

A program has been completed that investigated the effect of the urban multipath environment on mobile antennas at 900 MHz. The program involved the construction of several mobile antennas, careful measurement of these antennas on an antenna range to determine their characteristics in a controlled environment, and measurement of their characteristics in the multipath environment of cities. Measured results were compared to computed results and pattern range results were compared to field data to permit generalized conclusions to be reached. The results of the second phase of the program, measurements made in the mobile multipath environment, are presented. Analysis of this data shows that gain antennas have significantly less gain in areas where multipath propagation predominates and that the increased aperture of the gain antennas provides no significant smoothing of the received signals in the multipath environment.     

平面左手结构在微波器件及天线设计中的应用

自从2001年首次实现人工左手媒质以来，人们一直致力于制作大带宽、低损耗、易集成且具有左手特性的微波器件与天线．本文着重介绍两种基本的左手结构在平面微波电路中的应用，其一是左右手复合结构，其二为互补开口谐振环结构．近年来，这两种结构在微波器件及天线设计中得到广泛研究与应用．本文总结了国内外在这两个方面的研究进展，并结合我们在这方面所取得的成果，对平面左手电路的原理和应用进行了详细分析和说明。     

Mobile antenna gain at 900 MHz

A program has been initiated to investigate the effect of the urban multipath environment on mobile antennas at 900 MHz. The program involves the constructuion of several mobile antennas, careful measurement of these antennas on an antenna range to determine their characteristics in a controlled environment, then measurement of their characteristics in the multipath environment of cities. Measured results are compared to computed results to permit generalized conclusions to be reached. This paper presents the results of the first phase of the program; measurements made in the controlled pattern range environment.     

一种天线阵面精度补偿优化方法

大型天线阵面在机械载荷和温度载荷的综合作用下产生的变形,可以导致其电性能波动甚至失效;实际应用中,常采用补偿结构修正该变形以保证其性能。文中给出了一种阵面精度补偿方法:阵面工作前利用调整机构使天线阵面产生预变形,从而使天线阵正常工作时变形引起的增益损失最小化。通过建立天线阵机电热耦合有限元模型,构建优化数学模型计算调整机构最优调整量,并使调整量公差最大化,达到了改善天线阵电性能、减轻加工安装难度、降低制造成本的目的。