Investigation Of Modal Analytical Method On Microwave Transmission Line Discontinuity

Recently, as microwave system develop towards complication and higher frequency application, the discontinuity of transmission line has attracted great attention. In this paper, microwave transmission line discontinuity has been investigated by using finite difference time domain algorithm and perfectly matched layer (PML) absorbing boundary-condition.Fundamental principle of FDTD, essential knowledge of transmission line and microwave net are introduced in this paper at first. Then transition of microstrip line to slot line and microstrip lower pass filter are simulated, their scattering parameters are gained as well. The simulative results are compared with the results of commercial software HFSS and experimentation and agree with each other, which proves that the FDTD simulation is correct and effective.Microwave transmission line is an important component of microwave system. With the development of microwave technology, microwave systems are more and more complicated and the application frequencies are higher. A tiny change of structure or disturbance will lead great influence to microwave system, so higher performance of transmission line must be asked. In this paper, a deep investigation of transmission line discontinuity has been done. Based on FDTD simulation, transmission lines have been analyzed by making use of multi-postprocessing methods. First, the cut-off frequency and propagation (or attenuation) constant are gained by transverse field resonance (TFR) method and time and space Fourier transform (TSFT) method. Then making use of hybrid 2D/3D- FDTD algorithm, the field component distributions of dominant mode and high order mode are obtained, and then the propagation (or attenuation) constant and energy conversion of different modes are calculated. Finally, using singular value decomposition (SVD) of frequency domain field component, the mode field component distribution, dispersive relation and energy conversion are obtained as well. Results of different methods compared with each other, partial results also compared with HFSS results and theoretical values and agree with well.All the postprocessing in this paper is achieved by using matlab program. The date disposal is flexible and convenient, and the research on high order mode of complanate transmission line can not be achieved by HFSS. The research results also have great sense on improving transmission line performance and expanding its application.