FDTD Algorithm And Its Applications On The Analysis Of PBG Microstrip Structure

Due to its simple configuration, easy application, and excellent performance, photonic bandgap (PBG) is widely used in radio frequency (RF) circuits recently. In this paper, the scattering parameters of microstrip PBG structures, which are influenced by the shielding metallic enclosure as well as the finite ground plane, are analyzed using the Finite-Difference Time-Domain (FDTD) method. Meanwhile, the stopband variations due to the interval and number of the PBG periodic structures as well as the structure's size and shape are also simulated by FDTD. Moreover, an approach to improve the perfect matched layer (PML) absorbing boundary condition (ABC) and two kinds of field components visualization method are presented.An approach to improve anisotropic PML absorbing boundary based on Gedney's anisotropic PML is presented. The novel PML is much more effective in codes realization than the original one and it can provides a -20dB reduction of reflection errors.In order to observe the real-time electromagnetic field components calculated by FDTD, two visualization methods are given. The first method takes advantages of MATLAB (a mathematical software) to visualize EM field, which is easy but inefficient. The second method uses the direct screen drawing technology provided by Quick Win in Visual Fortran, with the benefits of high calculation efficiency and excellent interaction for FDTD programs.The S-parameters of microstrip PBG structures are achieved through Gaussian pulse excitation and Fourier transformation. Then, the influence of the metallic enclosure on a shielded PBG structure as well as the finite ground plane on an unshielded one is analyzed. The variations of the interval and number of the PBG periodic structures as well as the structure's size and shape are also discussed in detail. The simulation of the microstrip PBG structures using FDTD provides many useful conclusions, such as 7-9 periods of PBG structure can produce excellent stopband effect and too close metallic enclosure will shift the whole band to higher frequency. As a result, an optimum PBG configuration method is provided, which is directive and practical in applications of microstrip PBG structures.