蒸发波导微波超视距信道衰落特性研究思路漫谈

简单分析了蒸发波导传播的信道特征,试探性地构建了一个蒸发波导信道传输的模型并通过仿真实验得到了相关数据,最后对信道传播损耗功率进行分析,得出了蒸发波导微波超视距信道衰落的相关特性,以供广大同行参考与借鉴,以期推动我国海面蒸发波导超视距信道研究工作的发展。     

蒸发波导微波超视距信道衰落特性研究

针对利用海上蒸发波导效应的微波超视距通信,在三条不同距离跨海电路上开展了外场试验。基于测试数据,统计L、S、C和X频段超视距信道的衰落幅度、深度和速率,对比分析了蒸发波导和对流层散射信道的快衰落特性。并根据大气波导和对流层散射传播预测模型,统计比较了实测和模型预测路径传播损耗。结果表明与对流层散射信道相比,蒸发波导信道衰落幅度、衰落深度和衰落速率均较小,传播预测模型可有效的预测蒸发波导的慢衰落特性。     

蒸发波导模型与微波超视距传播试验对比

海洋蒸发波导是实现近海面超视距电波传播的重要环境,利用蒸发波导模型和电波传播数值算法是获取路径损耗的主要途径.基于海上平台约7个月测量的水文气象参数,对比了Paulus提出的PJ模型和美国海军研究生院(Naval Postgraduate School,NPS)提出的NPS模型,同时利用约1个月的海上超视距传播测试数据...     

粗糙海面建模及其在蒸发波导传播中的应用研究

海上蒸发波导微波超视距电波传播对舰载雷达的运行具有重要的影响. 本文基于粗糙海面电波散射特征和海面高度分布概率密度函数,提出了一种考虑海面遮蔽影响的海上电波传播计算方法,并与两种不包含遮蔽影响的粗糙海面建模的计算结果进行了模拟和试验对比. 计算结果为:1）随着计算频率和风速的增大,不同粗糙海面处理方法的计算结果差异增大,对应位置的路径损耗差异可达10 dB;2）基于试验数据的对比初步显示采用考虑遮蔽影响改进的抛物方程模型预测的路径损耗精度相对较高,粗糙海面对电波的遮蔽效应是蒸发波导传播损耗计算中的一个重要因素;3）试验结果为不稳定大气时采用NPS蒸发波导模型、稳定大气时采用PJ蒸发波导模型预测大气折射率剖面,所预测的路径损耗要优于采用单一蒸发波导模型的结果. 本文所得结果对海上电波传播计算和大气波导的反演等具有参考价值.     

基于蒸发波导传播的雷达定位误差研究

大气参数满足一定条件(修正折射率梯度小于0)时会形成大气波导,利用大气波导可实现雷达的超视距探测。由于近海面易形成蒸发波导,利用蒸发波导实现雷达的超视距探测已成为目前舰船雷达最实用的方法之一。雷达电波射线在不均匀大气中传播时会产生折射误差,为提高舰船雷达的定位精度,必须研究雷达在蒸发波导中超视距探测时的大气折射误差。根据电波传播理论,利用电波射线描迹技术,建立了舰船雷达在蒸发波导中实现超视距探测时的大气折射误差模型。仿真实验表明,蒸发波导条件下雷达超视距探测目标时的大气折射误差较大,且计算时不能采用常规的折射误差计算方法。     

海面蒸发波导微波超视距通信可行性分析

海面蒸发波导是海洋环境下可有效增强无线信号而实现超视距传播的一种媒质。介绍了海面蒸发波导的基本概念、传播机理以及国外研究概况,分析了利用这种信道资源实现微波超视距通信的可行性,表明其传输信道稳定,具有较高的通信可用度,可以为海域船只之间、船只与陆地或岛屿之间的远距离大容量信息传输提供一种新型的可用通信手段。     

蒸发波导条件下雷达超视距探测距离研究

首先,对蒸发波导条件下舰载雷达超视距探测距离进行研究,描述了蒸发波导形成机理,以及需要监测的参数.然后,分析了对舰载雷达实现超视距探测的3个条件,给出了舰载雷达作用距离表达式.最后,采用分步傅里叶变换求解抛物方程法对蒸发波导条件下雷达电磁波传播损失进行了仿真分析,并给出了上下边界和初始场的处理方式.仿真结果表明,蒸发波导越高,目标高度越小,发射仰角越低,雷达作用距离越大.     

蒸发波导传播的统计分析

全面介绍了中国电波传播研究所建所60年来,在对流层大气波导超视距电波环境及传播专业领域的研究及其应用情况,主要包括对流层大气波导机理与预测模型研究、大气波导探测感知与预测预报方法、超短波/微波超视距传播算法、无线电信息化系统装备超视距验证评估及信息保障等反映该领域国内相关技术的发展历程和最新研究成果,并结合实际应用需求提出了未来技术的发展趋势.     

海上超视距传输信号衰落分布分析

利用我国渤海海域X波段107 km超视距传输外场测试数据开展统计分析,给出了海上超视距传输信号的快衰落分布以及瞬时信号的快慢衰落组合分布.链路预估的理论结果表明：海上蒸发波导环境下的超视距传输信号电平远远高于散射传输电平,接近自由空间传输的情形.链路试验结果表明： 7月15日海上环境下的信号接收电平可比对流层散射传输损耗中值高40 dB,其信号幅度分布服从瑞利分布;7月18日的信号接收电平起伏较大,具有波导增强型衰落的特点,低电平趋近于对流层散射传输中值电平,信号幅度分布趋近于标准偏差在4~10 dB之间的瑞利分布与对数正态分布组合分布.     

94-GHz propagation in the evaporation duct

One-way, low-altitude radio propagation measurements at 94 GHz and simultaneous surface meteorological measurements were made on a 40.6 km, over-horizon, over-water path along the southern California coast to assess the effects of the evaporation duct on signal propagation. More than 2000 h of RF and meteorological data were recorded in eight measurement periods from July 1986 to July 1987. On this path, the transmission loss in a standard atmosphere is nearly 280 dB; the median transmission loss measured is approximately 220 dB. This significant decrease in loss is due to the evaporation duct. A propagation model is used to predict transmission loss from observed surface meteorology; predictions derived from 10-min averages of wind speed, air temperatures, sea temperature, and humidity compare favorably to the measured values. On average, the modeling underestimates observations by only 10 dB. The propagation model is used to predict transmission loss from an independent climatology of evaporation duct heights. A comparison of the modeled distribution to the observed distribution is favorable. The accuracy of the propagation model provides a strong justification for using it to assess the propagation characteristics of millimeter-wave communication and radar systems operating in many, if not all, ocean regions     

Statistical assessment of evaporation duct propagation

Over-the-horizon propagation from 0.6 to 18 GHz is presented in the form of accumulated frequency distributions of path loss, showing the comparisons between theory and two measurement programs. The path-loss theory is based on waveguide solutions for a family of refractivity/height profiles characterized by evaporation duct height in the range of 1 to 40 m. Annual frequency distributions of evaporation duct height have been prepared based on 15 years of marine surface meteorological observations and are combined with the waveguide path loss/duct height results to give accumulated frequency distributions from experiments performed in the Aegean Sea and the North Sea. Excellent agreement of theory and observation is noted in most cases     

海上蒸发波导条件下电磁波传播损耗实验研究

海上舰载雷达系统受蒸发波导的影响,经常会出现超视距探测现象,其超视距探测效能的发挥基于海面蒸发波导环境下电磁波的传播规律.介绍了2007年1月份和5月份在我国东南沿海海域开展的海上电磁波传播损耗测量实验,并将实验测量结果与基于抛物方程的电磁波传播损耗计算模型的计算结果进行了分析和比较,结果表明:电磁波传播模型传播损耗理论预测值偏小,对理论模型的计算结果偏小的原因作了分析.     

Frequency diversity effects of evaporation duct propagation

A comparison of 3, 9.6, and 18-GHz low-altitude over-the-horizon propagation (as influenced by the evaporation duct) is presented. Theoretical and experimental results are given for a 35-km over-water path, where the transmitters were located about 5 m above mean sea level and the receivers were located either 4-5 m or 18-19 m above sea level. Results are presented in terms of the one-way propagation factor in decibels at each frequency. Long-term cumulative frequency distributions of calculated and observed propagation factors are presented. Particular attention is given to the relative performance of each radio frequency to investigate frequency-diversity improvements that may be available on such paths. In most cases presented, there is a close agreement between theory and observations. It is concluded that substantial improvements in received signal levels are likely to be achieved in most areas of the world by a suitable choice of two frequencies in the 10-20-GHz range     

障碍物对蒸发波导中电波传播影响研究

利用快速傅里叶变换求解分段线性宽角抛物方程的方法,研究了单个障碍物和多个障碍物对海面上方蒸发波导中电磁波传播的影响,将光滑海面上有障碍物与无障碍物的蒸发波导中电磁波传播结果进行了比较和讨论。结果表明:随着障碍物的存在及传输距离和障碍物高度的增加,蒸发波导中电磁波路径传输损耗增大,这对评估海面上空含舰船和岛屿时蒸发波导的传输特性有重要意义。     

Radio propagation characteristics due to rain at 20-GHz band

Measurements of 20-GHz radio wave rainfall attenuation and cross-polarization discrimination due to rain have been conducted since July 1971 in Tokyo. There was a high correlation between rainfall attenuation and cross-polarization discrimination. Rainfall attenuation of 45 dB caused cross-polarization discrimination of 12 dB.     

一种基于海洋气象数据的蒸发波导传播统计方法

利用1982—1999年的海洋气象观测资料,根据PJ（PoulusJeske）模型计算蒸发波导高度,基于蒸发波导高度统计分析结果和大气波导传播模型,形成了一种可预测蒸发波导传播损耗统计特性的方法.选取我国南海某区域,计算了S波段蒸发波导超视距传播损耗中值,并分析了不同区域蒸发波导传播损耗的季节变化特性和蒸发波导的无线电系统可利用率.通过与微波超视距传播实验的结果比较,验证了该方法的有效性.     

风向对蒸发波导环境特性影响的研究

海上蒸发波导环境特性在具体应用时很少考虑风向的影响.应用伪折射率模式,对我国东海和南海部分近海海域的数据分析表明,在我国近海海域,陆地风(离岸风)和海面风(向岸风)对蒸发波导的环境特性有一定的影响,影响程度随季节和海域的变化而不同.蒸发波导环境与传播试验场地的选择及其试验数据的处理应考虑风向的影响.