中文摘要：

近地空间通信中链路损耗随着传输仰角的降低而增加。在低仰角传输中,大气传输损耗由于信道复杂度的增加而衰减严重。文中基于ITU-R的降雨衰减模型,结合低仰角远距离传输,分析了近地空间通信链路中冰/雨层与纬度位置的关系,并在不同频段,不同轨道高度对降雨衰减及雨衰导致天线尺寸的变化进行数值计算和仿真。仿真结果表明：在低仰角的传输环境中,降雨对近地空间通信链路的影响较大,不可忽视。其中S频段比X和Ku波段衰减小近20dB。最后总结了传输电波的工作频率、覆盖半径以及平台高度给降雨衰减带来的影响,以此来正确估计大气传输损耗对通信链路性能的影响,为近地空间在低仰角下远距离传输的链路预算提供了一个理论参考值。

英文摘要：

In near space communications transmission,the attenuation would increase with the decrease of elevation angle.With the condition of low elevation angle,the attenuation would increase as the complexity of transmitting channel rises up.Based on ITU-R rain attenuation model and the telecommunication at the low elevation,the relation between the cloud thickness and the latitudinous position is analyzed,the main factors that affect the attenuation characteristic in near space communications and the antenna diameter are simulated,as such,the attenuation is quantitatively computed in different frequency and different platform altitude.The results indicate that under the low elevation transmission the attenuations are serious and unnegligible.The rain attenuation of X and Ku band is obviously higher than that of S band in near space communications.Finally,the main factors that affect the attenuation characteristic are summarized.Meanwhile,the result could serve as a reference for engineering design of near space communications in low elevation transmission.