| Waveguide is a kind of guided wave structure used to guide electromagnetic wave directionally,and it is also an important feed structure of antenna.For the antenna radiation problem with complex waveguide structure,a reasonable modeling method of waveguide port excitation source can obtain accurate calculation results and greatly save computational resources.In addition,the transmission modes of waveguide ports with different structures are different.Based on this characteristic,it is often necessary to calculate and analyze the transmission mode of waveguide port in the research of modeling method of waveguide port excitation source.To solve the above problems,this thesis first realizes the calculation method of waveguide port mode based on finite difference method and finite element method.On this basis,considering that the moment method is a full wave numerical algorithm with extremely high theoretical accuracy,the Green’s function established by the moment method naturally meets the Sommerfeld radiation boundary condition,which can not only reduce the consumption of computing resources,but also obtain high computational accuracy when dealing with open domain problems.Therefore,Mo M is used to analyze the antenna radiation with complex waveguide structures.By combining the waveguide port mode calculation method,a high-precision equivalent model of the waveguide port excitation source is established in Mo M,and the fast algorithm of Mo M is applied to solve the practical engineering problems,which is conducive to strengthening the technical accumulation of electromagnetic field numerical calculation methods and electromagnetic simulation software.The main work of this thesis is summarized as follows:(1)The calculation method of waveguide port mode based on finite difference method is realized.First,the differential operator in the partial differential equation satisfied by the waveguide port is approximated by the difference formula using the difference principle,and the waveguide port surface is divided by the structured grid.For the regular waveguide port mode,more accurate calculation results can be obtained.By comparing with commercial software,the correctness of the waveguide port mode calculation method based on the finite difference method in this thesis is verified.Compared with the analytical method,the finite difference method can calculate the arbitrary waveguide port mode without analytical formula.(2)The calculation method of waveguide port mode based on finite element method is realized.Firstly,the variational equation satisfied by the waveguide port is established by using the variational principle,and the longitudinal field component on the grid node is expanded by using the node basis function.On this basis,the tangential field component of the waveguide port surface is expanded by adding the edge basis function.By assigning the degree of freedom to the edge,there will be no false solution when calculating the filled port of non-uniform medium,and the singularity problem caused by the connection part of conductor and medium is solved,which can be used to solve the filled port of non-uniform medium.Compared with the finite difference method,the finite element method can maintain a higher calculation accuracy when calculating the waveguide ports with complex shapes,and can calculate the waveguide ports filled with non-uniform dielectric,which has a wider application scenario and scope.(3)The modeling method of waveguide port excitation source based on equivalent principle and mode matching method in Mo M is proposed.Firstly,the equivalent model of arbitrary N-port waveguide port structure is given by referring to the equivalent principle and the theory of mode matching method.Then,the transmission mode of the waveguide port is calculated by using the finite element method,and the specific mode and transmission parameters satisfied by the waveguide port are extracted for external excitation of the target antenna.Finally,the surface integral equation satisfied by the object is established by Mo M,and the high-precision waveguide port excitation source model in Mo M is established.The experimental data show that the method in this thesis can not only ensure the integration of mesh generation in the process of the simulation solution of the antenna using Mo M,but also meet the demand of the main mode and high-order mode excitation of any waveguide port in the method of moments on the premise of saving computing resources.(4)The calculation process of MOM is accelerated by introducing parallel MOM and multilayer fast multipole,and the practical engineering problems are solved.Firstly,the multilayer fast multipole method and the parallel method of moments are used to calculate the waveguide slot antenna fed by a rectangular port,respectively.Compared with the measured results,the acceleration effect of the method of moments fast algorithm and the correctness of the method in this thesis are verified.Secondly,the actual antenna model with irregular waveguide structure is calculated and compared with the results of other full wave analysis methods,which verifies the effectiveness and universality of this method in calculating the antenna with complex waveguide structure in practical projects. |
