Research On Characteristics Of Near Vertical Radiowave Propagation In The Ionosphere

Near vertical incidence skywave communication and reconnaissance is an economical and effective method to solve the "blind area" problem of shortwave.In this mode,the radio wave is directly reflected from the ionosphere to the earth surface,so the received signal is irrelevant with the topography influence.It is especially suitable for using in mountainous areas and jungle areas with complex topography.This thesis uses the three-dimensional ray tracing method to construct near vertical incidence skywave propagation links based on international reference ionosphere,analyzing the propagation characteristics of near vertical incidence skywave,and accurately generating the point-to-point near vertical incidence skywave link is,including radio frequency,elevation angle,attenuation,field strength,etc.The near vertical shortwave communication experiment is carried out to evaluate the effect of near vertical communication.The main work is as follows:1.Ionospheric characteristic influence analysis on short-range skywaveAiming at the complex changes of ionospheric propagation characteristics with solar activity,season,local time,longitude and latitude,the influence of ionospheric distribution characteristics in different regions,distances,frequencies,seasons and periods on short-range skywave propagation is studied,including the construction of background ionosphere environment and background atmosphere,near vertical skywave propagation links grnerated by three-dimensional ray tracing technology,and analysis of ionospheric characteristics impact on short-range skywave propagation.2.Accurate generation of short-range skywave linkAiming at the fixed communication and reconnaissance range,the correlation model between the elevation angle and the ionospheric environment,the ground distance,radio frequency is studied.Frequency selection of short-range skywave communication of different ionosphere environment and distribution characteristics is researched.Based on the propagation characteristics of ionosphere,the study of ionospheric absorption attenuation prediction models and reconnaissance,field strength estimation,and signal to noise estimation are carried out to support for short-range communication.3.Near vertical shortwave communication testThe near vertical shortwave communication tests are carried out at the great circle distance of 100 km,200km and 400 km.The communication effect is evaluated by signal to noise and bit error rate.The semi-empirical model and electronic collision model of ionospheric absorption attenuation and signal to noise of near vertical incidence skywave link are tested and verified.