我刊论文成果形成国际标准

《电波科学学报》2006年第5期发表的"视距链路的雨衰减预报模式研究"一文中提出的地面视距雨衰减预报模式,已被国际电信联盟采纳,替代了国际标准     

水面反射引起场强变化及最佳分集接收天线高度差计算

电波在视距范围内传播时,除需考虑自由空间随距离而衰减的特性,还需考虑诸如地面反射和水面发射等造成电波强度的变化.接收天线在接收到电波直射波的同时,也接收到了反射波,尤其是电波传输通过河流、湖泊和大海等水面会使传播的信号随气候等因素的变化而急剧变化.研究水面变化影响电波传播的特性,并给出克服环境引起电波传播影响的方法十分...     

低轨卫星通信电波传播的双线模型

从陆地移动通信中电波传播的双线模型出发,根据低轨卫星通信的特点,提出了一种适用于低轨卫星通信电波传播的双线模型.通过对模型的分析和计算,得出了自由空间衰减随卫星仰角变化的规律.在仿真过程中,假设了接收机在卫星轨道面内和轨道面外两种情况,分别对TE波和TM波的路径增益进行了讨论.结果表明,由于地面反射的存在,自由空间的衰减在只有直视路径的基础上产生了起伏振荡.合理利用这些规律,对于低轨卫星信道建模和卫星通信接收机设计具有一定价值.     

电磁波传播的云雾衰减特性研究

研究了云雾对电磁波传输的衰减特性,在云雾衰减理论模型基础上,给出了云雾衰减工程计算模型,该模型所需参数少、计算简便,且误差符合工程计算要求,仿真分析了电波频率、温度、发射角度及成雾类型等参数对雾特征衰减率的影响。当无线电波的频率高于10GHz时,需要考虑云和雾对电波的衰减;当频率高于50GHz时,云、雾对电波的衰减才显得重要。云雾对电磁波传播的衰减随着电波频率、温度、发射角及水汽含量的增大而增大。     

我刊论文成果形成国际标准

《电波科学学报》2006年第5期发表的"视距链路的雨衰减预报模式研究"一文中提出的地面视距雨衰减预报模式,已被国际电信联盟采纳,替代了国际标准ITU-R P.530-13建议中的地面视距雨衰减预报模式     

电波沿随机粗糙海面绕射传播衰减研究

CCIR提供的电波沿海面绕射传播的衰减曲线只适于光滑海面，为了计算电波沿粗糙海面绕射传播的衰减，研究了适于工程计算的电波沿光滑表面绕射传播衰减的计算公式，然后推广到随机粗糙海面，绘制了衰减曲线并和CCIR以及其他经验公式计算的结果进行了比较。     

近海覆盖若干问题的探讨

首先得出近海覆盖电波传播最大视距距离,根据海面电波传播的二波传播特性推导计算电波在海面传播的无线传播损耗,随后分析了雨、雾、云对近海覆盖电波传播的影响,给出了雨、云衰减计算公式。最后根据得出的结果分析了台湾海峡和渤海湾两处海洋环境近海覆盖的电波覆盖及其传播损耗。     

一种特殊GDOP场景下的NLOS传播识别算法

在地面无线定位中,影响定位精度的最大因素是电波的非视距( NLOS )传播误差,定位估计前识别收发信机之间电波是视距( LOS )还是NLOS传播是提升定位精度需要研究的重要课题。为此,先对一种基于交叉面积的NLOS 识别算法进行改进,然后提出了一种针对特殊几何精度因子( GDOP)场景下的NLOS识别算法———分步检验算法。该算法采用两步进行识别,先用数据检验筛选出测量样本中的LOS测量值,再用改进的交叉面积算法进行识别。仿真结果表明,分步检验算法在特殊GDOP场景下具有良好的识别性能。     

卫星广播通信中的雨衰减研究及抗衰落策略

本文介绍了影响I0GHz以上频段卫星广播通信系统面临的主要电波传播问题,重点介绍了无线电气象、雨衰减统计预报、雨衰减动态特性等方面的研究进展.基于我国统计数据建立的电波环境数字地图是进行可靠电波传播效应预测的基础,新提出的雨衰减统计预报模式具有更高的预测精度,基于我国站点实测数据建立的衰落斜率预报模型更能符合我国区域的电波传播特性.文章对当前主要的抗衰落策略进行了介绍和对比.在高频段卫星广播通信系统中更合理的利用电波传播研究成果,采用合理的抗衰落策略,可以优化系统设计和资源配置、提高系统性能.     

电波传播模型介绍分析

地面电视广播发射的无线电波以大气作为无线信道进行信号的传递。在地面电视广播规划的覆盖和干扰分析过程中,需要对信号场强进行预测,因此针对无线电波的传播特性,建立相关电波传播模型对地面电视广播规划非常关键。本文简要介绍几种地面电视广播规划计算所使用到的电波传播模型。     

Measuring the Polarization Parameters of Rain by Inverse Scattering

The theory is presented for one method of determining the effective polarization parameters of the rain medium in the problem of polarization information processing of detecting target. The determination of the effective polarization parameters of the propagation medium is from the data of propagation measurements over a line-of-sight link. The polarization parameters ? the effective average value, σ the effective standard deviation and F the effective shape parameter of the propagation medium are obtained by means of the method of inverse scattering, showing a good agreement with the data from direct measurements.     

Holographic reconstruction of source distributions from microwave height-gain curves

Using the fast Fourier transform (FFT) algorithm, computer-reconstructed images of radio sources are obtained from conventional height-gain measurements over line-of-sight propagation paths for microwave frequencies of 2 and 4 GHz. The height-gain curves are regarded as one-dimensional microwave holograms.     

Prediction of breakpoint distance in microcellular environments

Experimental studies of path loss distance dependency in line-of-sight microcellular propagation almost always show a dual-slope behaviour. However, there is disagreement in the literature over the best way to predict the breakpoint distance that delineates the change in path loss distance dependency. A new breakpoint equation is presented, the predictions of which are in excellent agreement with breakpoint distances observed in various propagation studies     

Effect of thunderstorm on microwave line-of-sight propagation

Thunderstorms frequently occur during the months of April and May over Calcutta. The behavior of microwave signal propagation during such storms has been studied, utilizing a terrestrial microwave line-of-sight link. Storm period is characterized by an increase in signal level with deep fluctuations.     

Some New Results of Propagation Measurements and Their Application for Planning Transmitter Networks

To improve the coverage with medium frequency (MF) transmitters, new results of propagation measurements have to be recognized. Experiments were made to draw ground conductivity maps and to evaluate new propagation curves. Further measurements were begun to get information about the propagation with different polarization at MF. Great interest exists in preparing new frequency ranges for practical application. First experiments were made in the 11-12 GHz area to study the influence of terrain and the troposphere on propagation. On a 56-kin beyond line-of-sight path, field strength was recorded over a one-year period and the first results of mobile measurements in terrain were compared with propagation curves.     

大气折射对我国近地面无线电视距的影响分析

在无线电视距工程应用中, 常用等效地球半径因子表征大气折射的影响.为深入分析我国不同区域大气折射对无线电视距的影响, 定义了一种无线电视距因子, 以表征无线电视距相对标准大气视距的变化.基于我国区域近地面65 m高度大气折射率梯度数据, 得到了不同时间概率下我国区域无线电视距因子的时空分布, 结合拉萨、重庆、厦门、渤海湾、西沙、乌鲁木齐典型地区无线电视距因子的时间概率分布和季节变化, 分析给出了我国区域无线电视距因子的时空分布特征.分析结果表明, 我国不同地域无线电视距存在显著的时空变化, 并可导致无线电系统最大覆盖区域的显著时空变化.这些结果可为我国不同区域无线电系统设计和覆盖性能评估等提供参考依据.     

Tropospheric effects on design of line-of-sight space-diversity system

The successful application of space diversity to achieve a high propagation reliability over line-of-sight microwave links requires proper separation between diversity antennas, whereby the signals received at the antennas are sufficiently decorrelated. The multipath-propagation model is examined, and en expression is derived for the envelope correlation coefficient which is a function of antenna spacing and is dependent on the parameters of the troposphere.     

A comparative study of scintillation analysis over two line-of-sight paths at 6.7 GHz and 7.6 GHz

A comparison of the signal intensity fluctuations or scintillation of signal level, observed over two line-of-sight links is presented. These links are situated over Calcutta, DumDum-Andul (6.7 GHz) and Delhi, Delhi-Sonepat (7.6 GHz). The study reveals departures, in the occurrence and variation of the scintillation over the Calcutta path as compared with the path over Delhi. This deviation has been attributed to the large variation in humidity which exists in the coastal region, and also which plays a major role in microwave propagation in the troposphere.     

Frequency correlation of line-of-sight signal scintillations

The frequency autocorrelation of amplitude and phase scintillations of radio signals propagated over turbulent line-of-sight paths is calculated theoretically. The single scattering (Born) approximation to the electromagnetic response of the turbulent irregularities is used, limiting the results to small amplitude and phase variations. However, the results are valid for both Fresnel (near zone) and Fraunhofer (far zone) scattering. The calculations are made for an arbitrary model of the turbulent irregularities by using the spectrum method, which postpones the specialization of the analysis to a particular turbulence model until the wave-propagation aspects of the problem are completed. It is shown that the signal variations on adjacent carrier frequencies have high correlation for frequency separations comparable to the carrier frequency for all propagation conditions, indicating that the "medium bandwidth" for line-of-sight paths is very large. This also means that there should be negligible pulse distortion for high-speed data links or high resolution radars operating on line-of-sight paths. These predictions are compared with the few available experimental results.     

Theory for measuring the effective polarization parameters of rain from orthogonal linearly-polarized transmissions

The theory is presented for one method of determining the effective polarization parameters of rain from propagation measurements over a line-of-sight link. The method requires the transmission of orthogonal linearlypolarized signals and a set of three amplitude and two relative phase measurements. Approximate equations are given for determining both instantaneous and «statistical parametric» values of the effective parameters in a twoparameter Gaussian model of the raindrop canting angle distribution. The instantaneous values could be useful for comparison with in-situ measurements, while the statistical parametric values are required for prediction of rain depolarization statistics.