Study On Signal Transmission Characteristics Of Dynamic Sheath Of Hypersonic Vehicle

The plasma sheath will be produced around hypersonic vehicles due to the severe friction with the ambient air,then leading to air temperature raise,and finally complex thermal chemical reaction between high temperature gas and the spacecraft surface material when it reentry into the earth's atmosphere.The plasma sheath can attenuate and block comulication signals,which is ‘blackout' phenomenon.The plasma sheathon the surface of the aircraft is a complex electromagnetic phenomenon,which is a dynamic changing environment on the time domain and frequency domain,and cannot be solved using conventional wireless communication transmission theory and method,therefore leading to mismatch between the ultrahighspeed spacecraft Tt&c communication system and the existing communication system.In this article,the dynamic plasma sheath communication environment is analyzed from the angle of the wireless channel,and the character of ultra high speed vehicle dynamic plasma sheath channels is also researched.In view of the dynamic plasma sheath complex stochastic dynamic changing electromagnetic environment,the dynamic characteristic is analyzed in frequency domain and time domain.The electron density distribution modelof dynamic plasma sheath layer is built on the basis of the theory of wave propagation in plasma classic.The complex transmission coefficient of dynamic plasma is calculated and analyzed.The dynamic plasma sheath effects on measurement and control signal transmission is researched.In this article,the main work and methods as follows:1?When hypersonic vehiclesreentry into the earth's atmosphere,the existing turbulence and ablationmake the flow field instability changeon the surface of the aircraft,and the biggest change frequency can reach several hundreds KHz,which seriously affect the measurement and control communication.In researching,parameters are divided into small scale changes,which leads to electron density in the plasma sheath layer dynamic change in time domain and frequency domain.Temperature,pressure,and the change of electron density isproportional on the hypersonic vehiclessurface dynamic plasma sheath layer.According to the aircraft surface temperature and the pressure distribution and power spectrum density,we get plasma sheath layer time-varying electron density obey gaussian distribution,and its power spectral density obey the distribution that is the combining formof exponential distribution and gaussian distribution.2.The complex transmission coefficient of the dynamic plasma sheath reflects the magnitude of the amplitude and phase offset of the dynamic plasma to the measured signal.The time series of plasma electron density need to be obtained when calculating the complex transmission coefficient of the dynamic plasma sheath using the equivalent wave impedance method.In the study of dynamic plasma sheath,we stratify it in the direction of vertical plane.In this paper,We use two-dimensional filtering method to generate two-dimensional time-varying electron density.After obtaining the dynamic plasma electron density sequence,the plasma complex transmission coefficient is calculated by the equivalent wave impedance method.By analyzing the attenuation coefficient and the phase shift coefficient obeying the Gaussian distribution,the power spectral density is also the combination of the exponential distribution plus the Gaussian distribution.3.The influence of the dynamic plasma sheath on the propagation characteristics of the electromagnetic wave is analyzed by simulation and experimental method.There is a comparison between single-carrier signal and DQPSK signal through dynamic plasma before and after the spectral characteristics of the changes.It was found that due to the influence of dynamic plasma,other peaks appearexcept the carrier frequency.The same results were obtained in the simulated dynamic plasma experiment of the EB F8 channel simulator.In the simulation of the wideband signal DQPSK signal,the changes of the signal through the dynamic plasma before and after the eye diagram and the constellation are analyzed,and the bit error rate is calculated.The results show that the amplitude of the DQPSK signal is attenuated by the dynamic plasma and the phase is shifted.And with the increase of the dynamic plasma electron density,these changes are more serious.The bit error rate also increases with the increase of dynamic plasma electron density.After theoretical discussion and simulation results analysis,the study of dynamic plasma sheath channel characteristics can accurately reflect the dynamic plasma communication environment,Which provides a new theoretical basis for the establishment of communication system in complex electromagnetic environment.