The Finite-Difference Time-Domain Method And Its Application to The Analysis of Microstrip Antennas
In this thesis, issues related to the FD-TD method and its application are discussed. In particular, absorbing boundary conditions, use of signal processing techniques with the FDTD method, and the application of the FD-TD technique to analyzing microstrip antennas are studied.
A new theory called dispersive boundary condition (DBC) theory is formulated and developed. The concept of dispersive boundary condition is introduced first. Based on this concept, three dispersive absorbing boundary conditions are proposed from differing points of view. These DBC's are applied to microstrip and waveguide component analyses. Using these dispersive boundary conditions, great savings in computer memory and significant improvements in the accuracy of the FD-TD method can be achieved for dispersive structure analyses.
The use of digital signal processing (DSP) techniques for improving the performance of the FD-TD method is introduced. We demonstrate that the capabilities and the efficiency of the FD-TD method can be improved in several aspects due to the introduction of DSP. In the dispersive absorbing boundary condition studies, digital filter theory is applied to analyze and design DBC. Several DBC's have been unified by using digital filter theory, and it is expected that this will stimulate further development in absorbing boundary conditions.
Also, modern spectrum estimation and digital filtering techniques are used to improve the efficiency of FD-TD method in solving eigenvalue problems. It is demonstrated by means of numerical and experimental results that the efficiency of the FD-TD method for dielectric resonator analysis improves by about one order of magnitude. This new result makes it possible for the FD-TD method to be used as a practical tool for analyzing dielectric resonators.
The FD-TD method is used to accurately characterize complex planar printed antennas with various feed structures, including microstrip line feed, proximity coupled feed, aperture coupled feed, and coaxial probe feed structures. The validity of a coaxial probe feed model is demonstrated by a comparison of simulated and experimental results. For high dielectric constant substrate antennas, the dispersive boundary condition is employed to absorb strongly dispersive waves. In addition, several other new treatments have been tested for microstrip antenna analysis. All the numerical results obtained using the FD-TD method are compared with experimental results, and the comparison shows excellent agreement over a wide frequency band.