Study Of The Electromagnetic Field Distribution Under Evaporation Duct Environment

Evaporation duct is a typical kind of anomalous atmosphere structure near the seasurface. It can partly guide radio waves to distances far beyond the horizon with lessattenuation and change the characteristic of the electromagnetic waves propagation.Accordingly, the researches on the characteristics of electromagnetic wavespropagation and evaporation duct environment have great theoretical significance andare of great value to military on radar communication, detection and electronicwarfare.The paper describes the forming and parameter characteristics of evaporationduct and the impact on electromagnetic waves under evaporation duct condition. Usingthe atmospheric boundary layers'theory, the modified refractivity of evaporation ductis got under different atmospheric layer conditions, such as stable atmospheric layer,neutral atmospheric layer and unstable atmospheric layer.Through analyzing the Helmholtz equation, the parabolic equation is got, whichis satisfied with the electromagnetic wave under inhomogenous distribution ofatmospheric refractive index. The Fourier split-step method provides the solution ofthe parabolic equation. Furthermore, taking the neutral atmospheric layer as aninstance, Attenuation factor and basic transmission loss varying with space variablesare calculated in the evaporation duct near the sea surface.Through the four-dimension expression of transmission loss on two-dimensionspace of height and distance, the paper discusses the impaction of the antenna height,maximum angle and duct height on radio propagation in the evaporation duct under theneutral atmospheric layer condition and standard atmosphere. The conclusion is ingood agreement with that of the ray trace technique.