Preliminary plans for a propagation experiment in Mali

Measurements of propagation effects on satellite down-links to tropical locations are rare. This paper describes two experiments that will provide new and useful data for radiowave propagation in tropical Africa. A discussion of the African tropical climate is included that shows the wide range of rainfall patterns throughout the continent. Also, the broad distribution of climate in Mali, the West African country where the experiments will be located, is described. A rain-rate measurement programme involving autonomous terminals based on tipping bucket rain-gauges is presented. An experiment measuring the slant-path attenuation of the 12·5 GHz beacon of the ESA satellite OLYMPUS is described. The paper also discusses how the measured data in both experiments will be relayed daily from Mali to Virginia Tech by the low earth orbit satellite VaSTAR.     

Measurements of 11 GHz attenuation using the intelsat V beacon in Indonesia

A campaign of measurements in Indonesia has been carried out according to a co-operation agreement concluded between the Indonesian and French Administrations with the aim of estimating rain attenuation on slant paths. The experiment was planned using two earth-stations, at Cibinong and Padang, both receiving a K_u-band beacon from an INTELSAT V satellite, coupled with rain-rate measurements at a number of sites. Rain-rate statistics are given for several locations in the Indonesian Archipelago. Cumulative distributions of attenuation and simultaneous rain rate, obtained at the earth-stations, are presented. The analysis of the results has led to the proposal of an adaptation of the CCIR attenuation prediction method for low latitudes.     

Prediction of attenuation due to rain: Characteristics of the 0°C isotherm in temperate and tropical climates

A detailed investigation of the vertical structure of rain and of the characteristics of the 0°C isotherm height in both rainy and non-rainy conditions has been carried out in connection with the prediction of rain attenuation on Earth-satellite links. Radiosonde data have been analysed for eight and nine locations in the southern and northern hemispheres, respectively. The temporal, latitudinal variations and the relationship between the 0°C isotherm height and ground meteorological parameters such as rainfall, temperature and relative humidity, are reported. The equivalent rain height measured along the Earth-satellite link is compared with the heights obtained from meteorological data.     

CCIR data for slant-path propagation in tropical regions: A critical review

The development of methods for predicting the effects of the troposphere and ionosphere on Earth-space paths is a topic of major interest in the work of CCIR. A principal objective is that the methods have world-wide applicability and, being essentially empirical in nature, their development relies on the availability and voluntary contribution of world-wide data, as well as on a knowledge of the global behaviour of the propagation mechanisms involved. Despite some advances in recent years, CCIR propagation prediction methods continue to lack universal applicability, in particular in low latitude tropical areas. This is largely due to a shortage of measurement data for the regions concerned; hopefully, this situation is changing in view of recent efforts to establish appropriate propagation experiments. The paper reviews the current status of CCIR propagation data and information relating to the design of space telecommunication systems in tropical regions, making close reference to the studies and texts of CCIR Study Groups 5 and 6 (Propagation in non-ionized and in ionized media, respectively). Shortcomings in the available information and the lack of general world-wide applicability of the models, highlight the propagation effects for which further data are still required.     

Rain rate conversion for various integration time for equatorial and tropical climates

Rain rate statistics are derived on the basis of rain gauge recordings having effective integration times of 5 min or more. The conversion of such data to equivalent statistics for an effective integration time of 1 min is important to the design of both terrestrial and earth‐space microwave systems. Tipping bucket precipitation records for seven locations in South East Asia countries have been analysed and present the results of a testing activity performed on four conversion methods of rain rate integration time, from 5, 10, 30 and 60 to 1 min. Copyright © 2008 John Wiley & Sons, Ltd.     

热带无线电波传播研究进展及核心影响因素分析

热带无线电波传播研究是近年来电波领域重要的研究分支之一。综述了国际电信联盟(ITU)和国际无线电科学联盟(USRI)关于热带无线电波传播的主要研究内容和进展情况,分析了与热带无线电波传播相关的核心影响因素,包括雨衰、对流层闪烁、大气波导、植被衰落、盐度等,最后,指出了关于热带无线电波传播需要进一步研究的方向。相关内容可为热带无线电波传播的深入研究提供参考。     

Ku‐band diurnal fade characteristics and fade event duration data from three,two‐year,Earth–space radiometric experiments in Equatorial Africa

The move to provide direct to home (DTH) multi‐media services from satellites requires a number of new insights to be gleaned from the propagation effects that occur along satellite‐to‐ground paths. Annual statistics will not be sufficient to describe the likely performance of the link, nor will they provide information on the likely customer acceptance of the DTH service. What are required are the likely number of outages due to rain attenuation in a given period, their duration, the time between the outages, and the diurnal characteristics of rain attenuation along the link. This paper presents results obtained in three, two‐year, Ku‐band experiments in tropical Africa on diurnal attenuation effects, as well as on rain and attenuation event duration and inter‐event duration. The implications of the results are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

Comparison of measured rain attenuation in the 10.982‐GHz band with predictions and sensitivity analysis

The campaign to collect rain attenuation data on terrestrial links had commenced in Malaysian tropical climates for almost two decades. The terrestrial data so far collected have been greatly utilized to derive useful statistics for various microwave applications, such as frequency scaling, rain rate conversion factor, 1‐min rain rate contour maps, wet antenna losses, and fade slope duration analysis. However, there is still severe scarcity of rain attenuation data on earth–space links in Malaysia. The results of the 2‐year measurement (January 2009–December 2010) of rain rates and rain‐induced attenuation in vertically polarized signals propagating at 10.982 GHz have been presented in this paper. The rain attenuation over the link path was measured at Islamic International University Malaysia and compared with ITU‐R P.618‐10 and Crane global models in this paper. The test results show that the two prediction models seem inadequate for predicting rain attenuation in the Ku‐band in Malaysia. Sensitivity analysis performed on measured data also reveals that the sensitivity variables depend on rain rate. Copyright © 2014 John Wiley & Sons, Ltd.     

蒸发波导中电磁波异常传播特征研究及其应用

蒸发波导是海洋大气环境中一种典型的异常大气折射结构。它能够部分地陷获电磁波的传播,从而改变电磁波的传播特征。这种特性在雷达、通信、电子对抗等设备的使用方面具有广泛的应用。该文主要利用电磁波传播的抛物型数值方程和裂步傅里叶算法,通过仿真方法研究了蒸发波导环境下电磁波所具有的异常传播特征,并利用2003年8月大连海域的雷达异常探测试验作为应用实例,说明了蒸发波导对电磁波异常传播以及对雷达异常性能的影响。     

陆地高速移动环境下电波传播特性的建模与分析

采用有限状态的马尔克夫链得出陆地高速移动环境下电波传播路径的动态仿真模型。将模型与真实的陆地高速移动电波传播环境相结合,建立了更符合实际传播环境的电波传播仿真模型,通过该传播模型得出陆地高速移动环境下的电波传播特性。将得出的模型运用于较平坦地理环境,基站信号覆盖区域约为3km,存在视距(LOS)路径。通过仿真给出了高速列车在沿线不同位置和不同速度时的电波路径数目、各电波路径的衰减系数、延迟时间等,以及由此分析计算出的在该环境下的多普勒频谱、电平通过率等电波特性。最后,对这些仿真数据进行统计分析,证实了该传播模型的有效性。     

我国典型沙区中沙尘的物理特性

针对我国典型沙区的理论研究和实验结果，着重系统地讨论了我国塔克拉玛干沙漠等典型沙区的有关沙尘浓度，粒径分布，形状分布，介电特性等物理特性及其受环境因素的影响。     

Slant path rain attenuation predictions for Ku and Ka band frequencies from rain cell size distribution over a tropical region in southern India

Rain cell size distribution that provides an insight into the modelling of effective slant path length and also imperative for site diversity studies are carried out for a tropical inland location, Tirupati (13.6°N, 76.3°E), India. Rain cell size distribution obtained from 5 years (2013–2015 and 2017–2018) of Parsivel disdrometer measurements is observed to follow the power law. Reduction factor that accounts for the inhomogeneity of the rain along the propagation path for the region of study is modified in terms of the rain cell size distribution of the area. Slant path rain attenuation, a major propagation impediment at Ku and Ka-band links, is then studied using the results from the regional rain characteristics by modifying the CCIR 564-4 report. The attenuation results are compared with Garcia-Lopez, Excell, Bryant, and Ramachandran models while considering the ITU-R P. 618-13 as the standard model.     

DC and microwave characteristics of Lg 50 nm T-gate InAlN/AlN/GaN HEMT for future high power RF applications

The DC and microwave characteristics of L_g = 50 nm T-gate InAlN/AlN/GaN High Electron Mobility Transistor (HEMT) on SiC substrate with heavily doped n+ GaN source and drain regions have demonstrated using Synopsys TCAD tool. The proposed device features an AlN spacer layer, AlGaN back-barrier and SiN surface passivation. The proposed HEMT exhibits a maximum drain current density of 1.8 A/mm, peak transconductance (g_m) of 650 mS/mm and ft/fmax of 118/210 GHz. At room temperature, the measured carrier mobility, sheet charge carrier density (n_s) and breakdown voltage are 1195 cm²/Vs, 1.6 × 10¹³ cm⁻² and 18 V respectively. The superlatives of the proposed HEMTs are bewitching competitor for future monolithic microwave integrated circuits (MMIC) applications particularly in W-band (75–110 GHz) high power RF applications.