The Simulation Of Complex Electromagnetic Environment Based On Integrated Shooting And Bouncing Ray

The computational electromagnetic(CEM)is widely applied in practical problems,such as target recognition and stealth technology,antenna analysis and design,wireless communication and signal propogation simulation,how to handle those problems accurately and efficiently has drawn more and more attention for the recently years.In this dissertation,the shooting and bouncing ray(SBR)is further studied and improved.What's more,several efficient and valid methods and algorithm framework are proposed and implemented for different simulation targets,which expand the application range of SBR in practical problem.Based on the SBR and modified adptive division beam tracing(MADBT),the four issues include hybrid method SBR-MoM for analyzing complex large objects,hybrid method MLFMA-MADBT for analysis of antenna mounted on large-scale complicated platform,radio propagation simulation in complex indoor environment and large scale urban environment.Focusing on these four topics,we have proposed accurate and efficient methods after deep study.Firstly,a new efficient hybrid technique based on ray is presented,which combines the method of moments(MoM)and the shooting and bouncing ray(SBR)for analyzing scattering of complex large object containing some important intricate and small structure.The small structure is divided into MoM region and the remaining part of the object is allocated as SBR region.Furthermore,a novel and efficient coupling interaction between the two regions is considered to enhance the accuracy.For the MoM region,the interaction is the multi-bounce field or near scattering field from the SBR region.It is also considered the interaction from the MoM region to the SBR region by the reflected field.The proposed SBR-MoM method combining the advantages of both methods,accuracy and efficiency,is especially suitable for analyzing the scattering of complex large target with small structure.Secondly,an iterative and hybrid method which combines the multi-level fast multipole algorithm(MLFMA)and the modified adaptive division beam tracing(MADBT)is proposed for analyzing radiation patterns of antennas mounted on large-scale complex platform.MLFMA is adopted to analyze the antenna region,which can be treated equivalently as a point source(dipole)by using the oct-tree structure of MLFMA and fast far field approximation(FAFFA).Then the point source is modeled and converted into some intial beams launched to the BT region.The MADBT method is utilized to trace all the beams that effectively intersect with the platform and calculate all the effective beams' contribution to the final far field.By applying the ray-based MADBT method instead of the current-based physical optics(PO)method for the large platform,it can consider the multiple reflections inside the platform and highly enhance the accuracy especially for the platform with corner-reflector.At the same time,the MLFMA-MADBT method can also avoid the matrix vector product(MVP)of the MLFMA-PO method in each iteration and greatly reduce the memory consumption.What's more,the proposed MLFMA-MADBT method is mesh-independent while guaranteeing high accuracy level not only for the flat platform but also the complex platform with curved surfaces.By compared to the MLFMA-PO method,the proposed MLFMA-MADBT method has high predominance in memory usage and also obtains better accuracy and efficiency.In addition,a new hybrid propagation model of ray launching and Image based on the acceleration technique kd-tree algorithm for predicting the radio coverage in complex indoor environment is introduced.For each ray emitted from the transmitter,within the number of interaction(reflection or transmission),all the possible ray propagation paths can be searched for by the ray launching(RL)method and then the image method is applied to determine the valid paths.Finally,the receiver power strength can be calculated based on geometrical optics(GO)and uniform theory of diffraction(UTD).As expected,the proposed propagation model performs high computational efficiency and accuracy.Meanwhile,the kd-tree algorithm is also used to accelerate the intersection test of ray tracing,which greatly reduces the computational cost.Lastly,a modified adaptive division beam tracing(MADBT)technique is presented for the simulation of radio propagation in large scale urban environments.Beams launched from a transmitter are recursively traced by applying the MADBT method within the number of interaction and beam trees recording the propagation path info are generated.By traversing the beam trees,all the valid propagation(transmitted,reflected and diffracted)paths are efficiently determined.Then the receiver power strength can be calculated based on geometrical optics(GO)and uniform theory of diffraction(UTD)along the arrival paths.Because of the full space coverage of beam,the beam tracing can overcome the shortcomings of ray tracing,such as sampling errors,double counting and path missing,and avoid the divergence problem of ray tube,which ensures the accuracy of propagation paths.By tracing the continuous and minimum beams instead of a number of rays,the proposed method performs higher efficiency than the widely used ray tracing method.During the beam tracing procedure,several techniques are adopted to accelerate the calculation.A localized kd-tree is built according to the coverage area of the transmitter,which is more efficient than the global kd-tree to do the beam-triangle intersection during the tracing procedure.Then,a virtual simulation face(VSF)is generated to quickly get the receivers arrived by beams and speed up the searching for ray paths.Moreover,the OpenMP and the MPI parallel technique are implemented to further enhance efficiency and enlarge simulation scene size of the proposed method.The main research work of this dissertation is based on shooting and bouncing ray and modified adaptive division beam tracing.It provides effective solutions to analyze the electromagnetic scattering or radiation of antennas on electrically large platform by the hybrid method and the signal propagation simulation in indoor or urban environments.A large number of numerical results demonstrate the accuracy and efficiency of the proposed methods in this dissertation.The theoretical conclusions play solid foundations for the further research on this subject.