Research On Radio Wave Propagation Under Obstacle Environment

With the widespread use of information equipment and unmanned combat equipment,electromagnetic waves have become the main means of information transmission.Electronic war uses electromagnetic waves to detect and jamming enemy information transmission to achieve combat goals.Therefore,studying the characteristics of radio wave propagation in complex environments is an important basis for evaluating jamming effectiveness of the equipment,which plays a very important role in modern electronic war.In recent years,the two-way parabolic equation(2W-PE)method has become the main method for calculating radio wave propagation in the troposphere,which can efficiently and accurately calculate the spatial field value distribution.Therefore,this thesis mainly focuses on the research of radio wave propagation in the environment of medium ground and medium obstacles based on the2W-PE method,and combines with the method of moments(Mo M)and machine learning methods to verify and improve 2W-PE method.The specific research content of this thesis is divided into the following five aspects:(1)Firstly,the theoretical formula of the 2W-PE method is derived from the wave equation,and the algorithm framework of the 2W-PE method based on the domain decomposition principle in a complex obstacle environment is proposed.Discrete mixed Fourier transform(DMFT)and finite difference(FD)are used to solve the 2W-PE in each sub-domain,and the calculation method of 2W-PE is given by using global boundary conditions and surface impedance boundary conditions respectively,which lays a solid theoretical foundation to solve the problem of radio wave propagation in a complex obstacle environment.(2)The method of moments(Mo M)in a layered-medium environment is proposed to verify the accuracy of the proposed 2W-PE method in a complex medium environment.The PMCHW equation aiming at scattering problem for a single-medium obstacle located on medium ground is deduced,and the dyadic Green’s function of the electric field and magnetic field under the excitation of electromagnetic current in a layered medium environment is given,Hence the Mo M formula for the electromagnetic numerical calculation is obtained.On this basis,the proposed Mo M is extended to a more complex situation of multiple obstacles with different permittivity,thereby providing an effective means for accurately verifying the 2W-PE method.(3)In view of the complex obstacle environment,the proposed domain decomposition 2W-PE method and the Mo M are programmed and achieved,which analyses the calculation process of 2W-PE considering the multiple reflection and transmission processes inside the obstacle,and records whose level and reflection point of each propagation.On this basis,for the complex environment of different single rectangular obstacles,two rectangular obstacles and undulating obstacles,the field value distribution results calculated by the 2W-PE and the Mo M are compared to prove the accuracy of the 2W-PE,which also reveals the problems existing in the used impedance boundary conditions.(4)Aiming at the error in the results of current 2W-PE field value calculation comparing with those of Mo M,a new algorithm that uses machine learning algorithms to learn the boundary conditions to improve the calculation accuracy of 2W-PE is proposed.This method considers the existence of incident waves in different directions on the boundary of the obstacle,and determines the undetermined coefficients in the impedance boundary condition equations.Then,a fully connected neural network is designed,using the sample set generated by Mo M,through non-end-to-end training,so that appropriate boundary conditions can be obtained according to the given environmental parameters,which can improve the 2W-PE calculation accuracy.On this basis,the 2W-PE is further extended to the environment of undulating obstacles,with the longitudinal domain decomposition algorithm and the horizontal extension continuation algorithm introduced.After that,the undetermined coefficients of the boundary conditions are trained using a simple obstacle model to obtain accurate boundary conditions.In the end,the accuracy and effectiveness of the new algorithm are proved through examples,which lays a solid foundation for solving the problem of radio wave propagation in the real combat environment.(5)In order to meet the actual equipment application needs of the electronic countermeasure force,we apply the research content of this thesis to specific ground-based and UAV-borne electronic countermeasures equipment,and design a set of ground-based and UAV-borne radiation source jamming field strength analysis software system based on the 2W-PE method using MATLAB software.The system uses the map data to realize the simulation and demonstration of the equipment jamming field intensity distribution,which provides an effective means for improving the jamming performance prediction and combat effectiveness evaluation of electronic countermeasure equipment.