Research On Circulator And Antenna With FDTD

With the rapid development of communication technology, the devices for modern communications are required to be compact and wideband. Junction circulators and antennas are important equipments in communication system, which decide whether the communication system can achieve high performance. With the use of high power microwave system, people pay more attention to those circulators which can offer high power-handling capability.Communication system is developing toward larger capacity, multi-functions and intelligence; there have been increasing interests in dual frequency and wideband operation of microstrip antennas in recent years. The quick development of cellular telephone and wireless local area network (WLAN) provides broad platform for wideband dual-frequency antenna. It is very meaningful to design compact dual-band WLAN microstrip antenna.Computational electromagnetics is the combination of several subjects including computer technology, computational mathematics and electromagnetics. The finite-difference time-domain (FDTD) method is one of the most important methods in computational electromagnetics for its powerful capability. The goal of absorbing boundary conditions in FDTD is to achieve absorption performance with less computer storage. The radiation field characteristics of antenna can be computed by using near-field to far-field transformation in FDTD with huge amount of memory occupation and low speed. How to reduce storage demands is a research hotspot in FDTD.In the researches on waveguide junction circulator and dual-frequency antenna, many results are obtained by this dissertation. The results are as follows:Firstly, a novel broadband E-plane T-junction waveguide circulator with off-center ferrite discs is developed. This method can reduce the number of design parameters. FDTD method is applied to optimize parameters in the circulator. Fabrication and testing of the circulator are carried out. The correctness of the proposed method and calculation results are proved by testing results. Secondly, a mixed absorbing boundary condition based on Mur-UPML is proposed and applied in the analysis of circulator with off-center ferrite discs. The calculation result shows that the mixed absorbing boundary conditions can reduce the time for calculation significantly without reducing accuracy.Thirdly, a compact and dual-band micro-strip antenna for WLAN application is researched with organic magnetic materials. The influences of the slots on the antenna resonant frequency and the feed position on the antenna performance are studied by using reduced finite-difference time-domain(R-FDTD) method. The testing results show that the dualband antenna has good performance and can operate well in WLAN frequencies.The dissertation proposes a method to reduce storage demands in the near-field to far-field transformation in R-FDTD by reducing the data in near-field. Calculation results show that the method can improve the calculation efficiency with satisfied accuracy comparing with common R-FDTD method.