Simulation And Research Of Planar Microstrip Structure Based On FDTD Algorithm

Finite-Difference Time-Domain Method is a time-domain calculation method directly based on Maxwell curl equation.Compared with other numerical methods in computational electromagnetics,the difference approximation principle used by FDTD algorithm is easy to master,simple to calculate,easy to implement and universal.At the same time,FDTD algorithm can obtain a wide band of information through a single time domain calculation,so it is widely used in the electromagnetic field research.However,due to the particularity of the algorithm itself,it can only simulate the electromagnetic problem in the limited space.If the ideal absorption boundary conditions are set at the truncation boundary,all electromagnetic waves can be absorbed,so as to simulate the limited solving region.Therefore,setting the appropriate absorption boundary conditions can not only speed up the computational efficiency and improve the accuracy of the algorithm,but also make more efficient use of the computer memory.In this paper,FDTD algorithm is used to derive and study the three boundary conditions of special medium absorber,convolution perfect matching layer(CPML)absorption boundary condition and surface impedance boundary condition(SIBC),which are respectively applied to the simulation and analysis of planar microstrip structures based on MATLAB programming.The SIBC method is used to compute and analyze the microstrip structure quickly.At the same time,SIBC has the advantage of rapid analysis of planar structures compared to the absorbent and CPML absorption boundary conditions.The main contents of this paper are as follows:1.The basic equations of finite-difference time-domain method are introduced,and the absorption boundary conditions of Mur,CPML and SIBC are derived in detail from the principle of homogeneous wave equation and Maxwell equation of electromagnetic field.Finally,the expressions of each component of the absorption boundary conditions are obtained.2.In order to verify the absorption characteristics of electromagnetic wave by absorption boundary conditions at the truncated boundary,the FDTD algorithm was visualized by programming code written in MATLAB language,and the transmission characteristics of two-dimensional plane waves were simulated by absorption boundary conditions,and the correctness of FDTD algorithm was verified.3.On this basis,FDTD algorithm is used to simulate the microstrip filter,branch coupler and microstrip patch antenna.By changing the boundary thickness,iteration step and mesh size,the sampling voltages of the three structures are extracted.After a series of post-processing,scattering parameters are obtained.In addition,the simulation under different absorption boundary conditions is analyzed from three aspects: running time,occupied memory and error percentage.The simulation results show that with the increase of the number of iteration steps,the accuracy of simulation will be improved,but the calculation time will be greatly increased.However,compared with absorbent and CPML,SIBC boundary conditions have more advantages when calculating coarse grid or electric large size structures.The running time can be reduced effectively,the memory usage is minimized,and the percentage of error is in the range of 1.571% ～ 1.632% Therefore,SIBC absorption boundary conditions are useful for the rapid design of microstrip circuits and can be applied to the rapid analysis of dielectric structures.