Research On Tropospheric Duct Propagation And Its Applications

Tropospheric ducts in general, can guide radio waves to distances far beyond the horizon with less attenuation, and then severely impair some certain radio wave systems. Because of radio wave propagation along the ducts with enhanced fields on the order of the free-space-field, the problems of the co-channel interference are more complicate for communication systems, and for surveillance system such as radar system the problems can be radar holes or the extensions of detect range. So the researches on the characteristics of tropospheric ducts environment, propagation and its applications have great theoretical significance and its applications have great theoretical significance and are of great value to military.First, the paper describes the forming and parameter characteristics of tropospheric ducts and the impacts on electromagnetic waves under duct condition. Two current evaporation duct models in widespread operational use are presented and experiment comparison of these models is made using data collected from a boat. The limitations of evaporation duct models are also analyzedSecondly, through analyzing the Helmholtz equation, the parabolic equation is got, which is satisfied with the electromagnetic wave under inhomogenous distribution of atmospheric refractive index. The Fourier split-step method provides the solution of the parabolic equation. Furthermore, attenuation factor and basic transmission loss varying with space variables are calculated in the evaporation duct near the sea surface.Finally, applications of the anomalous propagation of microwave in tropospheric ducts are discussed: in connection with concrete radar parameters, effects of ducts on radar range and detection performance are discussed, the results obtained are of great value for the overall design of radar systems; by use of the interference standards of ITU-R, the co-ordination area of satellite earth-station under tropospheric ducts environment is studied ; by explaining the relationship between evaporation duct and advection fog, a new way to forecast sea advection fog from evaporation duct is provided.