| Atmospheric duct is a nearly permanent propagation mechanism due to the abrupt changes in the vertical temperature and humidity profiles just above the surface layer and a anomalous structure obviously different from the standard atmosphere, which can cause EM wave rays lying in the evaporation duct refracted towards the surface of the earth and make EM power trapped or guided in a thin tropospheric layer above the earth. Especially at tens of meter height close to the sea surface, interaction between the atmosphere and the sea water in surface layer makes the atmosphere structure more dramatic changes, and evaporation duct is one kind of the atmospheric duct frequently appearing in the marine environment. The resulting effect is an over-the-horizon propagation with less attenuation than in free-space conditions and radar detecting ranges can be greatly extended with duct propagation. The atmospheric duct phenomenon existence greatly strengthens or degrades the capability of the Radar, Communication, and Electronic Support Measures (ESM) system which are radio weapon system depending on electromagnetic radiation. How to overcome the negative impact on the electronic system resulting from the atmospheric duct propagation and how to make good use of the atmospheric duct phenomenon to improve the system performance of Radar, Communication and so on, the researches on the propagation characteristic of electromagnetic wave and its application in atmospheric duct have great theoretical significance and are of great value to the military.This dissertation gives a thorough research in depth on the subject including the parameter description and the forecast or prediction of the atmospheric duct and, and the propagation characteristic of electromagnetic wave and its application on Radar and Communication system in atmospheric duct. The specific investigations are followed below as:First, the formal condition and the parameter characteristics of the atmospheric duct and the impact on the EM-wave propagation are studied. Some kinds of the forecast and prediction technologies of the atmospheric duct are discussed, and the experimental measurement and the environment characteristics of the atmospheric duct in China sea are analyzed by some experiment data. By the atmospheric boundary layer theory, the dissertation discusses the modified refractivity profile of the different atmosphere layer in evaporation duct and the some parameter models of the modified refractivity, and the modified refractivity inversion by radar sea clutter are analyzed in atmospheric duct environment.Secondly, Geometrical Optics theory is an effective way to describe the electromagnetic-wave propagation problem in a condition of high-frequency approximation. By the ray-tracing technique, the dissertation analyzes the propagation path of the radio-wave rays at standard atmosphere and in evaporation duct for vividly describing the ray curvature and the over-the-horizon propagation. Based on the actual problems of the radar target detection in atmospheric duct environment, the ray-tracing technique is used to analyze the sight range, the sight elevated angle and the sight height. The error modification of the sight range, the sight elevated angle and the sight height respectively at the standard atmosphere and in the evaporation duct is compared, which is important to the radar target detection in atmospheric duct.Thirdly, the parabolic equation and the Fourier split-step method (FSS) with perfectly conducted smooth boundary are analyzed, and the flattening transform of the parabolic equation with irregular terrain and the mixed Fourier split-step method (MFT) with finitely conducted boundary are studied further. The radio-wave propagation theory and the solution with non-uniform horizontal refractivity in atmospheric duct, rough sea surface and irregular terrain are obtained. Based on the antenna theory, the relation between the direction function and the aperture distribution for the radiation of the EM field is discussed, and the beam-forming method for low sidelobe and narrow main beam suitable for the atmospheric duct propagation is analyzed. With the parabolic equation method and the basic theory of the radio-wave propagation, the transmission loss was calculated at the neutral atmospheric stratification in the evaporation duct near the sea surface and at standard atmosphere. The space characteristic of the electromagnetic field was presented in evaporation duct. The impaction of the duct height, antenna height and grazing angle on radar detection ability was analyzed under the neutral atmospheric stratification condition in the evaporation duct and at standard atmosphere by the pseudo-color map. The numerical simulation can present the space field distribution effectively rather than the ray-tracing technique. The research offers the reliable basis for predicting the blind area of the radar system. The one-dimension rough sea surface is simulated by Monte Carlo method on the basis of the sea spectrum. The knife-edge clearance of maritime digital terrain is effectively realized by the Wavelet analysis to broaden greatly the radar detection range for the modified parabolic equation. Based on the parabolic equation, the radio-wave propagation with rough sea surface in evaporation duct and with irregular terrain is analyzed. Fourthly, A method based on zero memory nonlinearity (ZMNL) is proposed to simulate sea clutter in evaporation duct environment for modeling radar signalling. The method identifies the relation between the K-distributed parameter of sea clutter and the evaporation duct height. The correlated K-distributed sea clutter is simulated at a certain duct height and detecting range. The application process of this method for clutter simulation is described. The simulation results prove the validity of the method for modeling sea clutter in evaporation duct.Fifthly, With the experimental data on the over-the-horizon microwave communication in China sea on summer day, the median level of signal, the fading amplitude, the fading depth and probability distribution are analyzed. The results show that the day variation of the fading amplitude has a high degree of significant correlation with the day variation of the evaporation duct height. Comparing with the communication equipment capability and the propagation loss on the basis of the evaporation duct characteristic in southeast sea of China, the propagation mode of the over-the-horizon microwave communication is mainly the anomalous propagation of the evaporation duct. Statistical analysis of the measured data of the over-the-horizon microwave communication is of great value to the system design and optimize the performance of microwave communication systems.Sixthly, based on the characteristics of EM multi-path propagation in marine atmospheric duct and the Markov birth-and-death process in finite space, path number in marine atmospheric duct is presented. The excess delay three-parameter model is proposed according to the experimental data with approximate Rayleigh distribution, and the model parameters are determined by the minimum variance criteria. The angles of arrival (AOA) is estimated by MUSIC algorithm and simulation results show MUSIC algorithm can significantly increase the SNR at AOA. Furthermore, a multi-eigenpath channel model is proposed to simulate the microwave transhorizon communication signal in atmospheric duct environment The channel model identifies the relation between multi-periodical delay components and subeigen-components. The simplified algorithm of subeigen-signal is proposed based on signal-to-multipath ratio (SMR). The multi-eigenpath channel model contributes to the system design and performance optimization of marine microwave communication system. Finally, the communication system modulated by ASK, PSK and FSK is simulated at the basis of the multi-eigenpath channel model of the atmospheric duct, and the bit error performance of the system is analyzed for designing the marine over-the-horizon microwave communication system.
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