Study On Some Problems For Radio Wave Propagating And Scattering Through Space Plasma

With the rapid development of space science and technology in recent years, people hasextended their exploration area to the interstellar space. While the space plasma environmentis the basic condition for people’s space exploration activity. The environment of spaceplasma includes ionospheric plasma environment, the star and the outer space plasmaenvironment, etc. At the same time, for the exploration activity of the unknown space isconcerned, people put forward a higher requirement on radio communication system, whileradio wave propagation environment is the significant component in communication systemwhich can not be neglected. So radio wave propagation in space plasma has attracted moreand more attention of the scholars. Based on the fundamental theory of the radio wavepropagation and scattering in plasma, emphasis is put on investigating on the related problemof dust plasma, space debris in ionosphere, ionospheric heating and plasma sheath. The mainworks are as follows:Firstly, the basic knowledge of plasma environment in ionosphere is introduced. Then themain factors of space plasma which have influence on the electromagnetic wave transmissionand scattering is analyzed. According to the empirical models of electron density and iondensity in plasma, the numerical methods of radio wave propagation in plasma which includeWKB of radio wave propagation, transmission matrix, FDTD and ray tracing is discussed.Secondly, the transmission of electromagnetic wave in dust plasma becomes a researchsubject which draws more and more attentions. The charge and discharge model of the dustparticles in space dust plasma is discussed. The electromagnetic scattering of the chargingdust is taken as the scattering from the central dust particle and the scattering from debyecloud out of the particle, the Mie-Debye scattering of the dust plasma is analyzed, theelectromagnetic scattering characteristics of the charged dust in dust plasma with equilibriumstate is examined. Finally, according to the charging equation and electrostatic equilibriumequation of dust particle, the relationship between the charge number of dust particle and dustparticle radius is calculated. On the basis of the space environment simulation, thecharacteristics of electromagnetic wave reflection and attenuation of dust plasma layer in theupper atmospheric environment is obtained with transport theory. It is found that theattenuation of electromagnetic wave by the dust for a fixing frequency of EM wave isproportional to electron density, dust particle density and dust particle radius.Thirdly, as we have already known, space debris keeps running in orbital space, and itwill increase with the development of human space activity, which is a heavy threaten to the safety of spacecraft operation. According to the increase and decrease factors of the spacedebris, the distribution model of space debris is studied. Then, on the basis of ionospherequasi parabolic model, the ionosphere electron density distribution is analyzed to get theelectron density distribution contour map of the interferential ionosphere, and scatteringcharacteristics of the ionospheric irregularity is investigated. The electromagnetic scatteringanalytic solution of ellipsoidal debris has been deduced by the scale transformation theory.Then, by using Born approximation and by taking the ionospheric irregular infield as theincident wave, the radar cross section of the irregularity and space debris is derived. Thenumerical results show that most of the energy of radar wave is scattered by the ionosphericirregularity to the forward direction and near around, which has a significant impact on theground based radar detection of the debris. When the frequency of electromagnetic waveincreases, the influence of irregularity on debris detection will reduce.Fourthly, ionosphere is a huge natural plasma physics laboratory. It is the carrier andchannel of the radio wave propagation. Based on the interaction mechanism of high-powerradio wave with the ionospheric plasma, the local change of the ionosphere is analyzed whenthe high-power radio wave is injected into the ionosphere. Under the given heating condition,electron density perturbation model is analyzed by electron’s effective recombinationcoefficients for the low ionosphere. However, for the high ionosphere, the heating mechanismis different from that in the low ionosphere with considering the drift of the electrons and ions.According to the electron and ion’s kinetic equation and continuity equation, the low and highionosphere electron density perturbation model are given, respectively. It is shown that theinjection of electromagnetic wave with high-power and high-frequency transmitting from theground base into ionosphere can cause a significant change on the electron density in theionosphere. The pump wave has a saturation effects on ionospheric heating. Finally, theattenuation of electromagnetic wave propagation in the heating ionosphere are calculated byray tracing method. Based on the above transmission model, the multi-path model ofionospheric heating is established, which indicates that ionospheric heating channel is atime-varying channel with disperse fading.Fifthly, when the aircraft flying in the space with high speed, the plasma cladding flowfield will be formed, which will have affects on the radio communication system that can notbe neglected. The sphere cone aircraft model is built in this paper. According to thecharacteristics of aircraft peripheral flow field, high speed aircraft circumferential flow field issimulated by the dimensionless control equations of axisymmetric, thermal chemical andnon-equilibrium flow. Considering the rotational symmetry characteristics of flow field, the temperature distribution of the aircraft peripheral flow field, the density distribution of eachgroup and the electron density distribution in different mach number are calculated.Finally, according to electron density distribution parameters simulated by the aircraftflow field, WKB and other methods are utilized to calculate the attenuation ofelectromagnetic wave in plasma sheath. By analyzing the plasma characteristics of the sheath,the phase shift of electromagnetic wave propagation in sheath is computed. Then, the triangleelement method is used to meshing sphere cone aircraft model. Based on the PO method, theRCS of sphere cone aircraft in different flight velocity is calculated. On the basis of plasmasheath characteristics and it’s attenuation of communication signal,“Blackout” forecastingmodel for the space communication is constructed. According to the reentry trajectory of theaircraft,“Blackout”is forecasted. Aiming at this issue, the electromagnetic window model isestablished. It is shown that the electron density in plasma sheath is considerably reduced bythis electromagnetic window and this method could reduce the risk of “Blackout”.