Research On Troposcatter Propagation Characteristics Based On The Turbulent Incoherent Scattering Theory

Troposscatter is a very important way of over-the-horizon propagation of ultrashort waves and microwaves segments,which is unrestricted by time and space variations.There are many propagation mechanisms for troposcatter,and the most important of which is the turbulent incoherent scattering mechanism.During tropospheric scatter propagation,electromagnetic waves are affected by inhomogeneous media such as turbulence,some of the energy is dissipated,causing transmission loss,and due to the spatio-temporal variation of atmospheric turbulence,the scattered electromagnetic waves will produce strong multipath effects,that affect the normal operation of the radio system.Therefore,the research on the propagation characteristics and channel characteristics of troposcatter can provide technical support for the design and evaluation of radio systems.In this paper,based on the turbulent incoherent scattering mechanism,the correlation between tropospheric scatter transmission loss and atmospheric refractive index structure constant is studied,which a deterministic propagation prediction model is proposed,referred to as LC model.Based on the experiments of the over-the-horizon propagation on land and at sea,the model was validated and analyzed.The Ray Tracing(RT)model is adopted to numerically simulate the transmission loss,coherence bandwidth,root-mean-square(RMS)delay extension and other channel parameters of the troposcatter propagation link.The major contents are as follows:1)Based on the turbulent incoherent scattering mechanism,the relationship between transmission loss and structure constant of the atmospheric refractive index,namely L-C model,is derived.The experiment of tropospheric scattering propagation is carried out to verify the correctness of the model which integrating structure constant of the atmospheric refractive index forecast by WRF(Weather Research and Forecasting)model.The results show that the theoretical and experimental results are in good agreement,which verifies the correctness of the model and the strong correlation between the transmission loss and the structure constant of the atmospheric refractive index.2)The experiment of over-the-horizon propagation is carried out to study the propagation mechanism of over-the-horizon propagation at sea.The differences and limitations of each prediction model are analyzed,based on the comparison of the prediction results among the L-C model,PJ model and NPS model.It is determined that both tropospheric scatter and atmospheric waveguide propagation exist,that only some experimental data are consistent with each model in the case of mixed propagation mechanism.3)The application of ray-tracing algorithm in troposcatter is introduced.Based on the turbulent scattering cross-section obtained by the approximation method,combined with the radar equation,the ideal conditions of troposcatter link is simulated by RT algorithm.The prediction results are compared with the L-C model and ITU-R P.617-4 model respectively,which verified the validity of the algorithm and program.Based on the power delay spectrum,the variation characteristics of channel parameters such as RMS delay spread and correlation bandwidth at different frequency and path length are analyzed.