Inhomogeneity Stimulated By Coherent Acoustic Source And The Application On The Scatter Communication System

Tropospheric scatter communication technology is a kind of beyond visual range(BVR) communication by using the inhomogeneity of tropospheric medium. Compared with the other kinds of communication, tropospheric scatter communication technology has many advantages such as long range coverage, large communication capacity and strong anti-interference, anti-interception, anti-destroy, anti-nuclear explosion, it can also work normally across complex terrain. However, this kind of communication has two fatal weaknesses, the first one is the scatter loss is great, the other is propagation characteristic is random for the channel of the scatter communication totally depends on the natural turbulence structure. So, it is meaningful to seek a kind of effective method to overcome weakness of the tropospheric scatter communication technology.This paper suggests a new technological approach by coherent acoustic source to stimulate the inhomogeneity of atmospheric refractivity, and applies this inhomogeneity on the tropospheric scatter communication technology. The key innovations in this thesis are as follows:This paper makes a simple introduction about acoustic propagation principle, superposition of acoustic wave and describes the acoustic interference phenomenon. On the basic of fundamental knowledge of the acoustic absorption in the atmosphere,then this paper analysis the variation of acoustic absorption coefficient with every various parameters. This paper calculates the acoustic attenuation factor with various heights. Then this paper discusses several basic acoustic sources and discusses the directivity of their radiation. At the same time, this paper establishes two kinds of coherent acoustic source modeling by the principle of wavefront splitting,including the modeling of spherical-surface acoustic source planar array and the modeling of cylinder-surface acoustic source linear array. And then this paper discusses the distribution of the acoustic pressure of the two kinds of acoustic array, it also simulates the array factors and discusses the variation relation between the distribution of acoustic pressure and the spherical-surface acoustic source planar array. Deviations of the relation between the effective value of atmospheric refractivity and the acoustic pressure, the instantaneous value of atmospheric refractivity and the acoustic pressure are made in this paper. This paper also discusses the relation between the atmospheric refractivity fluctuation and the dielectric constant fluctuation. This paper demonstrates where the maximum acoustic pressure value exists in the two kinds of array structure acoustic source and calculates the atmospheric refractivity fluctuation with the various height and other parameters. A brief introduction about the atmospheric scatter communication technology is made and this paper calculates the power of received signal when the coherent acoustic source exists, and by comparing the results when the coherent acoustic source doesn't exist, this comparison proves the feasibility of affecting tropospheric scatter communication by coherent acoustic source theoretically. In the end of this paper, the experimental modeling for proving the feasibility of affecting tropospheric scatter communication by coherent acoustic source-induced atmospheric refractivity fluctuation is first established based on the above content. By selecting the suitable parameters of the experimental system, the feasibility of affecting tropospheric scatter communication by coherent acoustic source is proved after analyzing the results in the experiment.This paper provides certain theoretical and experimental foudation for the development of the tropospheric scatter communication stimulated by coherent acoustic source.