The atmospheric duct in the troposphere is a kind of high-quality communication channel resource,which can support Beyond Line of Sight(BLOS) communication with high cost performance.First the trap refraction propagation mechanism and the classification of atmospheric duct are introduced.Then based on the experimental results of typical links in North China area and the Yellow Sea,the phenomenon of atmospheric duct and troposcatter dual-mode propagation is studied,and an analysis is given about the existenc...