Research On Theory And Application Of FDTD And Its Hybrid Algorithm In The Calculation Of Microstrip Antenna

As a kind of flexible and effective numerical algorithm,Finite Difference Time Domain(FDTD)is widely used to solve various problems in electromagnetic calculation.However,in practical application,due to the explicit difference characteristics of traditional FDTD,the time step of FDTD is limited by the stability condition.Therefore,FDTD in solving the problem with the structure of multi-scale,high Q value as microstrip antenna,faces to the contradiction between accuracy and efficiency.For the problems for the traditional algorithm,this dissertation proposed improved algorithms based on FDTD and local one-dimensional finite-difference time-domain with second-order temporal accuracy(LOD2-FDTD),and then used the improved algorithm to calculate and study the response of microstrip antenna and antenna array illuminated by high power electromagnetic pulse.The main contents and results of the dissertation are as follows:1.For traditional FDTD algorithm in simulation of electromagnetic field near microstrip antenna patch which changes drastically and has singularity,a lot of computational memory and time need to be taken.This dissertation introduced the distribution function of electromagnetic field near conductor edge into the FDTD,and proposed a conductor edge singularity processing technology.The experimental results showed that the method could achieve high computing precision and wider applicability without any increase in computational memory and reducing in computational efficiency.2.For calculating microstrip antenna with the multi-scale and high Q value structure,the traditional FDTD algorithm due to the limitation by the stability conditions needs a long simulation time.This dissertation employed the local one-dimensional finite-difference time-domain algorithm with second-order temporal accuracy,by increasing the time step to shorten the whole simulation time,proposed and studied the convolutional perfectly matched layer(CPML)absorbing boundary condition,near-far field transformation method,conductor edge singularity processing technology,and the algorithm combined with the subgrid technology.And their performance was verified by simulation experiments.3.For LOD2-FDTD in each time step needing to take a long time to solve implicit equations,this dissertation proposed a hybrid algorithm for FDTD and LOD2-FDTD.The hybrid algorithm employed the LOD2-FDTD with fine mesh in the fine structure,while employed FDTD with coarse mesh in other regions,so that only LOD2-FDTD region needed to solve implicit equations,thereby reducing the amount of computation.In addition,due to the LOD2-FDTD can adopt the same time step as the FDTD with coarse mesh,the time interpolation was avoided,which simplified the calculation steps,and ensured the stability of the algorithm.In this dissertation,the hybrid algorithms based on the subgrid technology which can cross the border of different medium and the Huygens subgrid technology were proposed.And the simulation results showed that the two hybrid algorithms ensured accuracy while improved the computational efficiency.4.For calculating the response of microstrip antenna illuminated by high power electromagnetic pulse,contradiction between accuracy and efficiency in traditional FDTD algorithm is particularly serious,this dissertation applied the proposed hybrid algorithm of FDTD and LOD2-FDTD to study the response of several typical microstrip antennas and antenna arrays illuminated by high power electromagnetic pulse.By the example of the microstrip antenna fed by microstrip line,comparing with the traditional FDTD algorithm,the proposed algorithm improve the computational efficiency while maintaining high accuracy.Then this dissertation studied the influences of incident direction,polarization angle,pulse type and parameters of high power electromagnetic pulse to response of the microstrip antennas and antenna arrays.