Atmospheric Propagation Characteristics And Capacity Analysis Of Terahertz Wave

Atmospheric propagation of Terahertz Wave is one of the most impotant component in science and technology of Terahertz,related to every application field of Terahertz.The unique characteristics of Terahertz made it great application potential in astronomy,nondestructive testing,lifesciences,safety,and high-speed communication.however,atmosphere is non-operative to the propagation of terahertz.In order to take advantages of terahertz wave availably,the propagation characteristics of terahertz need to be known well.Aimed at the problem mentioned above,the interaction of substance and THz wave is taken as the breakthrough,the more complete model of THz wave atmospheric propagation is presented.The validity of this model is verified by the corresponding experiment.Then the model is used to research the THz wave atmospheric propagation characteristics and the channel analysis of typical windows.The main works in this thesis including:Absorption is the one of the most important effect of the interaction of atmosphere and THz wave.Firstly,the influences of the interaction of THz wave and atmospheric gas as well as the line structure on radiative transmission are researched,on the basis of the HITRAN database,the effect of absorption and attenuation of the line absorption on THz wave is described in details.Aimed at the continuum absorption whose physical methanism is not yet clear,a semi-empirical method which is applicable to THz wave transmission is presented,experiment is used to obtain a set of coefficients of continuum absorption.Besides,the liquid water and complex dielectric constant water included in clouds will absorb the THz wave.We use the Rayleigh approximation method to calculate the absorption properties of different clouds on THz wave.We summarize the absorption property of atmosphere on THz wave conpletely through three aspacts:line absorption,continuum absorption and cloud absorption,then we build a complete model of THz wave atmospheric propagation of absorption and attenuation;Gain the capability to simulate the horizontal propagation and attenuation of broadband THz wave in real physical atmosphere;Analyze the key effect and regular of the attenuation and find the usableatmospheric windows.In addition,the transmitted spectrum in 0.3?2.0 THz measured data obtained from the THz-time domain spectroscopy(THz-TDS)technique is analyzed comparatively.,the results show a good agreement with calculation results for the intensity in windows and the location of the peak of absorption.Besides the effect of absorption,dispertion also influence the THz wave atmospheric propagation.In order to improve the model,the attenuation under the interactions of THz wave with atmospheric gas and hydrometeor.Firstly,the interaction of THz wave with atmospheric moleculars is analyzed through Rayleigh scattering theory,the result shows that the effect of dispertion can be ignored for the scale of atmospheric is too small.On the basis of the Lorenz Mie theory and Tmatrix method respectively,the absorption and dispertion in THz frequency range of spherical drip and nonspherical ice crystal are simulated numerically,a statistic attenuation model for terahertz wave in clouds is developed.The validity of model is verified through comparision with the results of ITU.We analyse the attenuation characteristics of THz wave in liquid clouds and ice clouds,then we find the attenuation of THz wave in ice clouds is more obvious which is of dozens dB higher than in liquid clouds.ARTS is used to construct the three-dimentional atmospheric layered structure,combining with the declining-path atmospheric attenuation model of THz wave,the attenuation of THz wave in some typical areas in arbitrary weather conditions is calculated to improve the model further which present the important parameter for THz wave satellite communication.Base on the THz pulse transmission lab builded by Research Center of Laser Fusion Chinese Academy of Engineering Physics,the effect of different vapor densities and transmission diatance on amplitude,phase and frequency spectrum of THz time-domain pulse is researched.The wave sharps are basically coincided of experiment and numerical simulation while a slight difference appears in amplitudes.When the experimental installation is modified to realize the 10m long-distance THz wave atmospheric transmission,the result of numerical simulation is in a good agreement with experiment for pulse wave sharp.It is conclude that the maximum wireless transmission data rate exceeds 20(Gb/s)between 0.1 and 0.5THz,which is much faster than through the single mode fiber(SMF)and more suitable for short distance communication.Combining the exsiting atmospheric THz transmission model and radiation transmission theory,a new model of the terahertz wave atmospheric propagation of attenuation and dispersion is developed,achieve the ability to simulate the transmission attenuation,path-loss and channel capacity of THz wave in real atmosphere at earth' s surface.Hereby,five usable channel are chosen:250GHz?340GHz?410GHz?500GHz and 670GHz.Through linear dispersion theory and principle of wireless communication respectively,the parameter of group velocity dispertion and channel capacity are accurately calculated physically.The antenna gain which effect the maximum wireless transmission data rate is analuzed.As we will show,the signals are not easily broadened due to the low group velocity dispersion;high data rates of more than 10Gbps can be transmitted via these channels if the antennas with high gains are used.In this thesis,the model of THz wave atmospheric transmission and channel analysis in complex weather condition are studied and diacussed comprehensively,which are contributed to understand fine structure of the THz wave atmospheric windows(including the locations of spectral lines,the widths of windows and the capacities of channels).In the light of these,we can make further advance of the radar property,improve the ability of high data rate communication.In addition,use the dispertion of THz wave atmospheric transmission,we can implement higher accuracy analysis of cloud characteristics,which lay foundations for 1)the qualitative semi-quantitative evaluation of the cloud characteristics obtained from satellited data;2)improve the quality of weather forecast;3)promote the development of new methods of remoting sensing clouds.