Modeling And Simulation Of Radio Propagation In Atmospheric Duct

Atmospheric duct is a layer of special atmosphere which is different from the standard atmosphere. It has a large negative refractive index so that the duct is able to make the ray curve. Because of the bending role of the duct, the ray is forced to curve down to the surface of the earth with a larger curvature than the earth itself and then reflect to the air. Consequently, some of the electromagnetic wave will just propagate forward in the duct layer. The appearance of atmospheric duct will form the blind area which part of the electromagnetic wave would have reached; but will also make part of the electromagnetic wave propagate to a far distance with a small attenuation. It is known to us all, the operating of all the Radio-Electronic system is based on receiving the energy and information carried by the electromagnetic wave, so the change of the electromagnetic field will influence the normal working of these equipments greatly. In all kinds of the atmospheric ducts, the evaporation duct which caused by the evaporation of the sea water emerged with the highest probability. It is really has the significance to make research in atmospheric duct, especially the evaporation duct, and the influence of the atmospheric duct to the Radio-Electronic system, and fide the way to make use of the atmospheric duct.In modern war, radar has become a very important weapons and equipment. With the development of the science and technology and the change of the war styles, electronic warfare, information warfare has become the first combat style in the war. Whether we can obtain the information of the enemy immediately and accurately has a close relation with the result of the battle. For radar system, the atmospheric duct will form the detection blind area, and also can realize the over-the-horizon detection. It has been a hot-spot in the radar field to realize the radar over-the-horizon detection by the evaporation duct.Several problems are discussed in the article, such as the propagation of the electromagnetic wave in the atmospheric duct, the influence of the evaporation duct to the performance of the radar system, and the consistency of the detection of the evaporation duct and the radar over-the-horizon detection. The significance of the atmospheric duct research, history and current situation of relative research at home and broad are all summarized. The knowledge of the characteristic parameters such as the appearance criterion, the height, the intensity of atmospheric duct are described in detail, by introducing the concept of the modified atmospheric refractive index and atmospheric refractive index, the necessary condition of the evaporation duct propagation are also given. In the process of studying on the basic theory of propagation of electromagnetic wave such as waveguide mode, parabolic equation, and geometrical optics, the ray tracing method is used to establish the propagation model of electromagnetic wave in the evaporation duct. Different types of duct propagation are simulated by computer in Matlab language, and the results are analyzed. Error correction model is also set up to give out the distance error, height error, and the angle error of the radar when working in the evaporation duct, the simulation work and results analysis are also operated. Finally, In order to test the correlation of the emergence of evaporation duct and radar's over-the-horizon detection, atmospheric duct tester is used which has high precision as well as fast response to measure the evaporation duct in the sky above the sea, at the same time, the radar which is fixed on the coast is used to carry out the detection. The actual results show that when the evaporation duct appears in the radar's work area, radar would be able to achieve the over-the-horizon detection, and the strength of the radar's signal is different with the change of the intensity of the evaporation duct. The radar would achieve far distance detection when the evaporation duct had a large intensity, and the target signal was clear and stable. The radar achieved very near when the evaporation duct was weaker, and the target signal was fuzzy and unstable. The consistency about the evaporation duct's actual measure and the radar signals'over-the-horizon propagation is proved.