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无线电波在对流层中远距离(超视距)传播时,由于电波在湍动不均匀的大气媒质上的散射,造成了接收端强的随机起伏;它是时间和空间的随机函数,常用统计方法来处理。本文研究了接收场强的起伏特性,得出了描述接收场起伏特性的表示式——衰落深度、衰落概率和衰落特续期。同时也讨论了这些衰落特性与通信线路参数,特别是载波频率和天线方向性之间的关系。分集接收对克服电波的快衰落具有很大优点。本文研究了分集信号经过合并(选择法、最大比值法、等增益法)后合成信号的衰落特性,并考虑了各分集信号之间的相关性。在进一步考虑了大气湍流的谱函数的情况下,对衰落特性作了某些补充和修正。本文所依据的实验结果是工作在频率100兆赫,距离为250公里的沪宁散射试验电路。结合着这些结果,最后讨论了特高频波段电波的固有衰落特性和分集效果。
When radio waves propagate long-haul (trans-horizon) in the troposphere, the strong random fluctuations of the receiving end are caused by the scattering of the radio waves in the non-uniform turbulent atmospheric medium; it is a stochastic function of time and space. Statistical methods are often used deal with. In this paper, we study the fluctuation characteristics of the received field strength and obtain the expressions describing the fluctuation characteristics of the receiving field - the fading depth, the fading probability and the fading duration. The relationship between these fading characteristics and communication line parameters, especially the carrier frequency and antenna directivity, is also discussed. Diversity reception has the great advantage of overcoming the fast fading of radio waves. In this paper, the fading characteristics of the composite signal after combining (selection method, maximum ratio method, equal gain method) are studied, and the correlation among the diversity signals is considered. With further consideration of the spectral function of atmospheric turbulence, some reflections and amendments have been made to the fading characteristics. The experimental results on which this paper is based are Shanghai-Nanjing scattering test circuits operating at a frequency of 100 MHz and a distance of 250 km. Combined with these results, the eigenfunctions and diversity effects of UHF band radio waves are discussed.