Finite Difference Time Domain Method In The Calculation Of Antenna Theory And Applied Research

The purpose of this thesis is to investigate the theory of finite-difference time-domain (FDTD) and its application to antenna analysis.Theoretically, the main work is the simulation of source excitation. By comparing the advantages and disadvantages of previous methods of source simulation, a novel simulation method of excitation source is presented. The details of the application to microstrip feed, waveguide feed and coaxial-cable feed using this simulating method are given. The antenna feed manner can be perfectly modeled accordingly, and less additional requirement for computer is needed. Using this simulation method, the time-domain waveform has complete fidelity.Beginning with the equivalence principal, two types of near-field to far-field (NFFF) transformation s are discussed systematically, i.e. frequency-domain NFFF (FD-NFFF) and time-domain NFFF (TD-NFFF). In TD-NFFF transformation, the concurrent-processing approach is used, where the contributions to far-field from the tangential electric current and magnetic current on the equivalence surface are calculated "on-the-fly" in step with the FDTD simulation. As a result, it is not necessary to store the tangential current components for every equivalence surface at every time step, and therefore reduce considerably computer storage required for the TD-NFFF transformation.Based on the previous theory, the FDTD method is used to analyze practical antennas, which include dipole antenna, microstrip antenna, log-periodic antenna and broadband resistance loaded monopoles. The particular problems that occur in the calculating of vary type antennas are discussed. The cross-section field of microstrip line and two-conductor line are analyzed, and the effect on the numerical result arising from the incident cross-section mesh size is discussed. In the analysis of log-periodical antenna the concept of diagonal field symmetric is introduced for the first time, and hence the calculating mesh size is reduced to half. In the calculation of circular polarization microstrip antenna, the effect of finite substrate is described. The combination of FDTD method with physical optics is also used to analyze paraboloidal reflector antenna in millimeter band. Using FDTD method, we obtains precise near fields of the feed because the computing areas include all the feed structure. The current on the paraboloidal reflector can be calculated by using physical optics, and then the far field of reflector can be calculated. All antennas concerned are of important value of engineering application.