Study On Some Problems For High Frequency Waves Propagating Through The Heated Ionosphere

In recent years,theory and experiment about the artificially heating ionosphere with HF waves have achieved great development owing to the progress of experimental facilities.On the one hand,field irregularities with different scales will be generated by heating the ionosphere with HF waves,and on the other hand,ELF/VLF waves will be excited by heating the ionosphere with modulated HF waves.These heating effects of ionosphere have great potential applications in wireless communication.On the basis of propagation theory of HF waves in the heating ionosphere,this paper briefly studies the scattering of irregularities,the generation of ELF/VLF waves and the Faraday effect of HF waves.The main work and conclusions are outlined as follows:1?Based on the geomagnetic coordinate system,the radar cross section of the irregularities is studied,and the variation of radar cross section with frequency in monostatic as well as bistatic is discussed.From which the specular scatter and field-aligned scatter models of irregularities generated by HF waves heating ionosphere are established.The effects of different transmitter sites and scattering sites on the track of the receiving path under specular scatter are discussed,in addition the variation of relative path loss,delay spread and coherence bandwidth of receiving sites under field-aligned scatter models are simulated and analyzed.2?Based on the field-aligned scatter models of irregularities,the influences were further studied by considering the different polarization modes.Under this condition,the variation of relative path loss,delay spread and coherence bandwidth with different frequencies and latitudes at different polarization types are discussed.The results show that the delay spread decreases while the correlation bandwidth increases with the increases of frequency.In the high latitude areas,the path loss is the smallest when the receiving and transmitting antennas use vertical polarization,while the one is the largest when the antennas are horizontally polarized.On the contrary,in the low latitude areas,the path loss is the smallest when the antennas are horizontally polarized and the largest when the antennas use vertical polarization.3?Based on the model of the excitation of ELF/VLF waves by amplitude modulated HF waves heating ionosphere,the electron temperature,disturbance of conductivities and the current density of ELF/VLF waves during the heating process by different periodic modulation schemes are studied.From the results we can conclude that the excited current density of ELF/VLF waves increases with the increasing of height,Moreover,under the same background conditions,the half-wave rectified wave modulation scheme is the most efficient one to generate signal at the modulation frequency,but the harmonic interference factor is the largest.The triangular wave scheme generates the best quality signal which has the lowest harmonic content.The square wave modulation scheme provides a compromise between generation efficiency and signal quality.4?Based on the A-H formula and the geometric relationship between the propagation path of waves and the ground considering the radius of the great circle,the Faraday rotation effect of HF waves propagating through the ionosphere is studied.Therefore,the variation of Faraday rotation angle and its depolarization loss at different latitudes,times and frequencies are analyzed,the result reveal that the depolarization loss increases with the decreasing of frequency and the increasing of electron density.