冰层下潜艇通讯中的电波传播问题

本文讨论了两种通讯方式的电波传输损耗。第一种通讯方式为地面发射台发射甚低频电波,经由地——电离层波导传播到达有冰层覆盖的海面,再穿透冰层和海水到达冰层下活动的潜艇的接收天线。第二种通讯方式为冰层下活动的潜艇,由水平漂浮天线发射中波或短波,穿透冰层,在海面上扩散传播,然后再穿透冰层到达在附近海域活动的另一潜艇的接收天线。计算了不同厚度的冰层对电波传输损耗的影响。     

圆极化天线在舰地图像传输中的应用

海面属于强反射平面,如何在强反射信道中抑制多径分量,实现信号可靠传输,工程中已积累了许多经验和方法。本文从圆极化天线抑制反射信号的原理、使用和安装的角度出发,提出了在海面强多径传播环境下,采用圆极化天线可以改善图像传输质量。试验结果表明:该方法切实可行,效果明显。     

空白电视频段下考虑船体晃动的海上无线电波传播特性研究*

为设计基于空白电视频段的海上无线传输系统,需要了解在该频段下无线电波在海面传播特性.在海上环境下,海面波动会引起船体晃动,导致发射和接收天线间的角度变化,从而影响海上电波传播损耗和通信链路性能.对海浪波动引起的船体晃动进行了三维建模,然后考虑地球曲率并结合晃动时天线角度改变引起的天线接收增益变化改进了海上电波传播损耗模型.借助该模型仿真分析了空白电视频段下不同船体晃动类型和在不同传播距离时对海上无线电波传输路径增益的影响程度.     

海面低仰角数字微波通信系统性能及体制分析

本文介绍了海面低仰角数字微波通信系统的特点，对海面电波多径衰落进行了理论计算，指出了通信系统抗衰落的方法和手段，并给出了一种抗衰落通信系统在海面通信试验中的测试数据。     

海面反射对一维相控阵天线影响的研究

海面反射引起的多径干涉效应,会造成宽波束雷达天线的俯仰波束分裂,导致雷达观测的盲区和目标跟踪丢失.文中从天线和电波传播的观点出发,分析了海面上单脉冲二次雷达询问天线的三维方向图特性,阐述了天线波束干涉的原理.详细分析海基一维相控阵雷达天线在姿态倾斜后的方位面和俯仰面干涉方向图,讨论了由于方向图变化引起的系统测角偏差,总结了降低多径影响的方法.     

庙岛群岛数字微波传输本地网介绍

数字微波通信由于具有通信容量大、传输质量高、建设周期短、维护费用低,投资省,抗干扰能力强,易于维护、管理等优点,目前在国内外已得到迅速发展,是一种先进的通信传输手段,并与光纤通信、卫星通信一起被称为现代通信传输的三大支柱。但是在海区,数字微波通信发展困难较大。这主要是由于电波传输与地形、地物、气候、频率及站距等条件有关。电波在海上传输时,海面反射系数大,反射干涉衰落严重;海洋上空容易出现大的水汽压强下降梯度,从而形成超折射,产生由大气波导引起的多径干涉,形成波导型衰落;另外海区     

散射通信海上应用研究

散射通信使用的电波频段大多为C波段。统计表明,散射通信电波在海上传播时,由于海面上空的大气折射指数等气象结构参数原因造成接收信号年中值电平损耗低于陆地;海面上空还经常出现利于电波传播的规则、不规则层反射现象及大气波导现象。上述原因使得散射通信设备在海面上使用时通信距离更远、信道传输容量更高,因此散射通信作为近海应急等通信的保障手段具有广阔的使用前景。     

基于合作分集的无线网络的研究

在发送端采用多根天线实现发送分集技术可以有效抑制多径干扰引起的信号衰落。但在很多实际应用中由于硬件复杂性和成本等方面的限制,不允许终端用户配置多根天线。针对此情况在物理层提出一种合作通信方式,利用网络中多个用户共享天线形成虚拟多天线,达到天线分集作用, 有效降低无线网络成本,提高网络的覆盖范围。研究了基于合作分集技术系统结构和合作方法,提出实现中涉及的若干关键技术。     

海上微波自适应数传系统设计

<正>受海面极其复杂的微波信道环境影响,传统的海上微波数传系统存在传输距离近、通信稳定性差、适应性不强等缺点。从提高天线增益以及增加传输自适应性角度设计了海上浮标船载间微波自适应数传系统,给出了系统的整体组成框图和主要模块的设计过程,针对浮标设计了可切换波束全向覆盖阵列天线,还设计了波束自动扫描切换以及速率自适应切换的通信协议。仿真结果与协议分析表明浮标天线增益高,自适应通信协议鲁棒性好,可保证系统传感器数据的高低速率远近距离的稳定自适应传输。     

部分浸没于海水中天线阻抗及辐射效率分析

针对海洋环境中浮标天线的辐射性能问题,基于海水中短波、超短波频段高衰减的特性,提出了以海面为分界面,将天线分为水上、水下两部分考虑的假设,建立了部分浸没于海水中天线的理论计算模型,开展了天线输入阻抗测试实验,验证了假设和模型的正确性.应用该模型,确定了天线的水上、水下部分阻抗共轭匹配条件下的工作频率范围,分析了不同入水...     

Characteristics of sea reflection fading in maritime satellite communications

The Japanese domestic experimental mobile satellite system (EMSS) has been studied to establish high quality channels for small vessels with compact and low-gain antennas. The present international maritime satellite communication system (INMARSAT) has also been studied for the next generation to extend services for small ships, for which the present ship terminals including the antenna systems are too large and too heavy. By using a low-gain antenna, however, multipath fading caused by sea reflections will become a serious problem in designing the new system. To take effective countermeasures to the fading effect, it is very important to get a better knowledge of the fading phenomena caused by sea reflections. From a standpoint of maritime satellite communications, experiments measuring the amount of fading were performed under various sea conditions and in two frequency bands. The wave height, which is considered the most important experimental parameter, was measured objectively by a wave rider buoy. The experimental results show that the amount of fading depends on a wave height and radio frequency and, as the most interesting result, as a wave increases above a certain level, the amount of fading decreases. These results are also discussed theoretically.     

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.     

基于数字浮标的噪声滤除算法的研究

当代军事技术发展迅速,数字浮标日益受到各国海军的重视,其主要应用于浅海中对水声信号进行识别、收集,存储、转发.本研究课题来源于某军工科研项目,主要针对浅海中的数字浮标在工作中如何对实时噪声进行滤除进行研究.文中主要介绍了自适应滤波特点及其算法的实现,然后对此算法在数字浮标上的可行性进行了研究,并结合DSP对其实现和验证,有效的证明此算法能在数字浮标上进行有效的噪声滤除.     

The antenna system of a distress buoy for use in a maritime satellite communication system (MARSAT)

Two different types of antenna systems for a distress buoy for use in the maritime satellite communication system (MARSAT) are described. The buoy radiates signals alternately on the frequencies 2182 kHz (medium frequency (MF) beacon) and 1.65 GHz (Lband beacon). TheLband antennas had to be combined with the MF antenna of a commercial buoy. The antenna systems have been tested with success during the application technology satellite (ATS-6) experiments and during a previous European Space Research Organization (ESRO) balloon communication experiment [1].     

Radar reflectivity of the ocean surface for circular polarization

If one transmits an electromagnetic wave, an electric field is set up in space. The earth's surface modifies the field and an interference pattern results. To calculate such a pattern one must know the reflection characteristics of the surface for the polarization of the incident wave. These are known for linear polarizations. Since a circularly polarized wave is a combination of the two linear polarizations, we can compute the reflection coefficient for circular polarizations by proper combination of the two linear reflection coefficients. This reflection coefficient is known for smooth sea conditions. In this paper the vector model of reflectivity for a rough sea is extended to include circular polarization. Reflection coefficients for the rough sea case are derived. Analytical expressions are given for the total received signal including the coherent and incoherent components. Receiver antenna polarizations of the same and opposite senses to that of the transmitter are considered.     

透地通信磁性接收天线设计

磁感应透地通信通过准静态磁场耦合的方式实现信息传输,可以有效解决传统电磁波通信中信道不稳定、传输距离近、天线尺寸大等问题。磁性天线尺寸小,灵敏度高,不易受电场信号干扰影响,适用于复杂的地下环境。基于磁性天线的基本工作原理,得出了灵敏度和信噪比的表达式,并根据磁芯与线圈不同参数对天线接收特性的影响提出了磁性接收天线的优化设计方案,最后通过公式计算与实验测量验证了天线优化设计方案的正确性与可行性。     

表面波放电狭缝天线辐射电磁场的三维数值分析

针对平板型表面波放电等离子体源,建立了表面波放电狭缝天线辐射电磁波模型,对狭缝天线辐射电磁场分布进行了三维数值计算,并与表面波电磁场进行对比分析,讨论了平板型表面波放电机理。结果表明:整个狭缝天线阵激发的电磁场是每个狭缝天线激发电磁场的线性叠加;狭缝天线阵直接激发的电磁场强度在临近波导壁面处很大,并且随着空间距离的增大迅速衰减;狭缝天线阵直接激发和表面波的电场均远大于各自的磁场,分析电、磁场对带电粒子的力作用时可以忽略磁场力的作用;表面波电磁场远大于狭缝天线阵直接辐射的电磁场,强电磁场范围也远大于狭缝天线阵直接激发的强电磁场范围,等离子体有增强电磁场强度、扩大强电磁场范围的作用。     

Sea surface imaging with an across-track interferometric syntheticaperture radar: the SINEWAVE experiment

An across track interferometric synthetic aperture radar (InSAR) is used to image ocean waves. Across track InSAR data were acquired during the SAR INnterferometry Experiment for validation of ocean Wave imaging models (SINEWAVE) in the North Sea using an airborne X-band radar with horizontal polarization. A wind sea system was imaged at different flight levels and with different flight directions with respect to the ocean wave propagation direction. Simultaneously, ocean wave spectra were measured by a directional wave rider buoy. Thus, the experiment data comprises synthetic aperture radar (SAR) intensity, coherence, and phase images together with in situ measurements. As shown in a recent theoretical study by Schulz-Stellenfleth and Lehner (2001), across track InSAR provides distorted (bunched) digital elevation models (DEMs) of the sea surface. Using SINEWAVE data the DEM bunching mechanism is verified with in situ ocean wave measurements available for the first time. It is shown that significant waveheight as well as one-dimensional (1D) wavenumber spectra derived from bunched DEMs and buoy data are in good agreement for small nonlinearities. Peak wave directions and peak wavelength detected in bunched DEMs and SAR intensity images are compared with the buoy spectrum. Peak rotations of up to 30° with respect to the buoy spectrum are found depending on flight direction and flight level. Two-dimensional (2D) spectra of bunched DEMs, corresponding coherency maps, and SAR intensity images are intercompared. The signal-to-noise ratio (SNR) of bunched DEM spectra is shown to be about 5 to 10 dB higher than the SNR of SAR intensity image spectra     

基于GSM通信的SZF型波浪浮标接收系统

SZF型波浪浮标是一种能自动、定点、定时（或连续）地对波浪水文要素进行测量的小型浮标自动测量系统。原本的SZF型波浪浮标系统的监测数据是通过岸站接收机进行数据接收。接收机可以符合野外接收需要,但为了能满足不同用户的需要,该文采用PC机接收,并编写友好的人机接收界面,实现数据的接收和使用。上位机接收系统使用VC＋＋开发,具备数据采集、实时显示、数据存储、数据查询功能。通过多次的试验检测和拷机测试,通信状况良好,能满足数据接收要求,提高了数据监测效率。该系统的开发大大地降低了海洋监测过程中的实时监测和后续数据处理的难度,可作为SZF型波浪浮标的配套软件进行推广。