Ka-band Earth-space propagation research in Japan

Earth-space propagation studies in Japan were originally concerned with measuring atmospheric absorption and rain attenuation by means of a suntracker and a radiometer, following which a number of long-term experiments were performed using various experimental and commercial satellites. The first experiments involving Ka-band Earth-space propagation measurements in Japan were carried out in 1977 using the Engineering Test Satellite Type II, and since 1978, these experiments have been conducted using Japan's domestic communication satellite. Based on these studies to date, the understanding of Earth-space propagation characteristics at higher frequency bands, modeling of propagation channels, and development of countermeasure technologies have shown dramatic progress. In Japan at present, advanced propagation studies are under way in wideband digital-transmission satellite systems for the forthcoming multimedia era. This paper summarizes recent study activities concerning wave propagation in Ka-band Earth-space paths and related topics, such as radiometeorology in Japan. Last, future plans for conducting Ka-band and millimeter-wave propagation experiments by using the Japanese experimental satellite “COMETS” and rain observations in tropical regions by “TRMM” are introduced briefly     

Prediction of slant path rain propagation statistics usingdual-polarized radar

The authors conducted a year-long experiment in which a dual-polarized S-band radar probed the volume surrounding two 11.45-GHz satellite downlink paths during rain. Accuracy was assessed by comparison to directly measured link attenuation with two 11-GHz beacon receivers 7.3-km apart at an 18.5° elevation angle, one colocated with the radar. Drop size distributions calculated from the radar horizontal reflectivity (Z_H) and differential reflectivity (ZDR) measurements were used to predict 11.45-GHz satellite beacon attenuations. The radar-predicted attenuations and those measured on the radio links agree, both on an event basis and in terms of annual cumulative distributions     

大气湍流中激光波束斜程传输的展宽、漂移特性

根据推广的Huygens-Fresnel原理推导了不同接收机高度斜程传输情况下波束的扩展半径.同时结合Mellin变换,导出了考虑外尺度情况下准直激光波束漂移方差模型,可以退化到不考虑外尺度时漂移方差.数值计算中应用ITU-R公布的随高度变化的大气结构常数模型,结果表明,斜程大气湍流中波束的漂移方差、扩展半径依赖于接收机高度和初始波束半宽.随仰角的增加,波束的有效半径和漂移方差不断减小;累积效应斜程传输波束受大气湍流的影响比水平传输要小得多.     

远红外无线光通信地-空斜程传输特性研究

随着空中平台的发展,无线光通信在斜向路径的应用需求也逐渐增多,但是大气效应对当前近红外系统的性能依然有较大影响.针对这一问题,本文提出使用远红外作为地-空斜程无线光通信系统的工作波长,基于物理模型和弱波动理论对远红外系统在地-空斜程上、下行链路中的传输损耗、光强闪烁指数和误码率(bit error rate,BER)进...     

激光斜程湍流大气传输平均偏振起伏

运用光子密度分布函数和采用大气折射率起伏Von Karmam湍流谱、研究了相干激光通过斜程大气传输时的平均量子偏振起伏。通过唯象方法导出大气折射起伏对光场相位调制关系,从而建立了斜程大气光子密度分布函数模型。基于斜程湍流大气光子密度分布函数导出了平均＂量子偏振度＂的解析关系。结果指出：湍流大气导致光束偏振度起伏满足零均值高斯分布,大气湍流不影响光子偏振度统计平均值。     

地空激光大气斜程传输湍流效应的数值模拟分析

大气湍流效应是制约各种激光工程应用的重要因素之一.采用多层相位屏的模拟方法,针对地空激光大气的长距离斜程传输进行了大量数值模拟,通过变化天顶角、光束初始半径和激光波长等传输条件,定量分析了光束的有效半径、相对真空扩展倍数、光斑质心漂移均方根和63.2%环围能量的平均功率密度等统计参量在不同传输条件下受湍流的影响程度和变化规律.结果表明:天顶角越大,湍流效应越强,光束受到湍流的影响越大;波长越短,光束受到湍流的影响越强;光斑的漂移随光束初始半径的增大而减小,且与波长无关;在湍流效应和衍射效应的综合作用下,光束有效半径和63.2%环围能量的功率密度随波长和光束初始半径均不是单调变化.这可为激光工程应用提供一定的理论分析和性能预测依据.     

湍流大气中光波闪烁的斜程问题研究

根据光波斜程传输理论以及随高度变化的ITU－R湍流大气结构常数模型,将水平传输的修正Rytov方法扩展到了斜程传输问题中。在零内尺度湍流谱模型下,得到了平面波入射时从弱起伏湍流区到强起伏湍流区闪烁指数随斜程Rytov方差的变化规律,最后讨论了闪烁指数随天顶角的变化情况。     

A new method of estimating microwave attenuation over a slant propagation path based on rain gauge data

A basic problem in estimating the microwave attenuation over a satellite-earth propagation path on the basis of rain gauge data is that, for a given precipitation event, the attenuation and the rainfall records very often do not have consistent detailed correlation. Such inconsistencies can be greatly reduced if the falling speed of the rain drops, i.e., 2 to 9 m/s for drop sizes of 0.05 to 0.7 cm, is taken into account. Adjustments in time and drop size spectrum are needed for data collected from field rain gauges to realize the actual rainfall along the slant path for correlating rain gauge data with measured satellite signals.     

The Ka-band propagation measurements campaign at JPL

OLYMPUS, the NASA sponsored, JPL-managed, Ka-band propagation measurement campaign carried out at Virginia Tech and many European sites, is discussed. The basic physics involved, the OLYMPUS experiment itself, and the advanced communications technology satellite (ACTS) program, the purpose of which is to demonstrate the feasibility of the Ka-band (20 and 30 GHz) spectrum for satellite communications, as well as to help maintain US leadership in satellite communications. are described     

System requirements for Ka-band Earth-satellite propagation data

Accurate estimates of the propagation impairments that affect link quality and availability and determine signal interference fields are essential for the reliable design of telecommunication systems and the efficient use of the electromagnetic spectrum. Recent announcements by commercial entities of their intent to use Ka-band spectrum to supply satellite services have heightened interest in propagation data and models for these frequencies. This paper provides a brief overview of Ka-band Earth-satellite systems and requirements in relation to the need for specific types of propagation data     

The slant path atmospheric refraction calibrator: an instrument tomeasure the microwave propagation delays induced by atmospheric watervapor

The Slant Path Atmospheric Refraction Calibrator (SPARC) has been developed to measure the water-vapor-induced propagation delay experienced by a radio signal traversing the atmosphere. SPARC measures the difference in the travel times between an optical and a microwave signal propagating along the same atmospheric path. Since the refractivity of dry air is similar for both the microwave and optical signals, the difference in arrival times is a sensitive measure of the water-vapor-induced microwave delay. The instrument is capable of measuring the difference in the optical and microwave travel times with an accuracy of 15 ps or better. SPARC was developed to provide an accurate, independent method for evaluating other techniques used to determine the atmospheric water-vapor-induced delay     

太赫兹波沿大气层倾斜路径的传输衰减

太赫兹大气传输是太赫兹科学技术及其应用的重要组成部分,它几乎渗透于所有的太赫兹应用技术领域.现有文献中所说的太赫兹大气传输基本都是水平路径的传输,而文章基于辐射传输、色散理论和Van-Vleck Weisskopf线型,结合喷气推进实验室(Jet Propulsion Laboratory,JPL)数据库,建立了太赫兹波沿大气层倾斜路径的传输衰减模型,对0.1～1 THz频段太赫兹波沿倾斜路径传输的吸收衰减特征进行了数值模拟研究.分析了低端太赫兹大气传输的窗口结构,为太赫兹地空通信提供了理论参考.     

Effects of ice depolarisation on Ka-band satellite-earth path in stratus rainfall events

In stratus rainfall events, the effects of ice depolarisation are evaluated using the CS-2 beacon signal and X-band radar observations. Although the ice effects described in terms of the deviation from theoretical rain depolarisation show a large variation according to the rain height, net ice depolarisations deduced above this height are relatively constant.<>     

Analysis of 11 GHz slant path fade duration and fade slope

The letter presents results of an analysis of fade slope and fade duration data collected at 11 GHz within the framework of the OTS propagation experiments in Europe. Evidence is given of the fact that on a statistical basis, fade slope and fade duration are related. This could possibly be used in uplink power control systems.     

沙尘暴对地空路径上Ka频段电波传播的影响

通过分析陆地上毫米波在沙尘暴中传播时的衰减和交叉极化分辨率，给出了一定高度毫米波传播的衰减和交叉极化分辨率的计算公式，并提出了一种计算地空路径沙尘暴衰减和交叉极化分辨率的等效模型。在不同的地球站点、不同的能见度、不同的沙尘粒子含水量、不同的粒径分布下进行了数值计算，并对结果进行了分析。     

斜程大气传输部分相干平顶光束的空间相干度

为了研究不同天顶角、传输距离、光源相干性以及湍流外尺度对接收面光束空间相干度的影响,采用广义惠更斯-菲涅耳原理和相位结构函数的平方近似,并运用张量积分的方法,得到了部分相干平顶光束通过斜程湍流大气传输后接收面光束空间相干度的解析表达式.结果表明,传输距离较短时,该光束空间相干度随两点距离的增加出现振荡现象,而传输距离较长时振荡现象消失;当传输距离给定时,天顶角越大,光束空间相干度的有效宽度相对较短.初始相干长度较短的该类光束其空间相干度的宽度不随传输距离的增加而减小;长距离传输后,光束空间相干性与光束初始相干长度不再有关.     

1.06μm激光的斜程大气衰减

根据大气透过率计算软件-CIRTRAN计算了乡村、城市、海洋和沙漠四类地区不同能见度条件下的1.06μm激光斜程大气透过率,经过分析和归纳,提出了一个直观而简便的计算公式.用三种不同的测量方法和LOWTRAN7作比较,证明该公式具有很好的准确度.     

Multipath propagation measurements on an overwater path in NewZealand

The results are described of a 140 Mb/s, 16 QAM digital microwave radio field trial to characterize multipath fading on a 60-km overwater route in New Zealand. Propagation data have been collected from the path between September 1985 and September 1986, and include one fading season of the Southern Hemisphere. The authors specifically apply and extend work on multipath fading by W.D. Rummler and others (1979, 1981, 1986). To the spectral data collected from the trial, a Rummler-type model (echo delay 6.35 ns) has been fitted. Distributions for the parameters a, b, and f_o ar observed to be similar to those presented by Rummler (1979) for the 26.4-mile Atlanta to Palmetto, Georgia path. Data which cannot be characterized well by the Rummler model include samples which show the evidence of a ray with equivalent long delay (⩾10 ns). This ray is either conjectured to be a sea reflection (however sea reflections are blocked at an Earth radius factor of k=4/3), or is indicative of the presence of more than one secondary ray     

11- and 18-GHz radio wave attenuation due to precipitation on a slant path

Measurements of attenuation at 11 and 18 GHz from precipitation have been made on a slant path over a three-year period in the Tokyo area using a sun tracker and a radiometer. Simultaneous rain attenuation measurements of a 2.9-km terrestrial path at 19 GHz were used to clarify the correlation characteristics between the terrestrial and the slant paths. The following results are presented: frequency, seasonal, annual, and elevation angle dependence of rain attenuation, rain rate distribution, effective distance, correlation characteristics of attenuation between slant and terrestrial paths, attenuation due to snowfall, and site diversity effect for a separation of 14.3 km at 18 GHz.     

基于OPNET的Ka频段卫星信道仿真建模与研究

针对Ka频段卫星通信信道中电波传播特性的研究,通过引入SAM模型和新的影响因子,包括雨滴大小、云雾及大气吸收等,分析了降雨及多因子对信道的影响,建立了Ka频段卫星通信信道仿真模型,并基于OPNET平台进行仿真。此模型能够更好地提供清晰的数学表达式．对卫星信道的研究提供了可靠数据。