The Foundational Investigation Of UC-PBG Applied On Microwave Components

Photonic crystals (or PBGs) refer to the artificial crystals with periodical dielectric structures. The periodical parameters of their dielectric structures and the wavelengths of EM waves are on the same order of magnitude. The fundamental characteristic of PBGs is the existence of band-gaps, namely, the photons within a certain frequency range cannot propagate in specific directions in PBGs. Another remarkable characteristic of PBGs is the realization of the localization of photons. Particularly, if some defects are introduced into PBGs, the photons whose frequencies fall in band-gaps will be localized in the defect areas, with the appearance of the narrow frequency range local state that ensues amid forbidden band. The working mechanisms of all the PBG devices relay upon those 2 characteristics. In microwave area, it's application include microstrip antenna, microwave filter, microstrip, and so on.UC-PBGs are 2-D plane PBGs. Their advantages include compact unit structure, low loss, and wide stop-band. This dissertation applies UC-PBGs to rectangular waveguide and rectangular microchip antenna, and discuss the transmission characteristics and slow-wave characteristics of UC-PBG rectangular waveguide, as well as the radiation characteristics of UC-PBG rectangular microstrip antenna, by numerical methods.The main contents of this dissertation are as follows:1. Brief introduction on band-gap theory of PBGs and its applications, principle of slow-wave system and its slow-wave characteristics.2. Introduction of microwave EDA simulation software - MWS, MAFIA, HFSS and their operating procedures.3. Calculation of the energy band of UC-PBG with EDA tool - HFSS. We constructed UC-PBG rectangular waveguide with that UC-PBG, and conducted numerical analysis of the transmission characteristics with MWS. The result proves the possibility of the propagation of TEM wave. In the forbidden band, UC-PBG can be equalized to a magnetic conductor (PMC). Thus the rectangular waveguide is equivalent to a pair-flat conductor, and the propagation of TEM mode can be achieved besides TE and TM modes and their combinations. That is coincident with theoretical analysis. From the resultant transmission modes, we also know the bandwidth of UC-PBG waveguide is 50% wider than that of the regular metallic rectangular waveguide.4. Due to the periodicity of the structure of UC-PBG, we estimated the possible existence of slow-wave in that structure. We conducted numerical calculation of the dispersion curve and coupling impedance curve with MWS and MAFIA, and the result shows that the first order backward wave of UC-PBG rectangular waveguide is slow-wave. This type of slow-wave system is suitable for operation in backward wave status, namely, application to backward wave vacuum electron devices such as carcinotron, etc. We also analyzed the effect of the size of the unit and periodical numbers of UC-PBG structures on the dispersion and coupling impedance, and found nearly no influence on dispersion but coupling impedance by changing them.5. radiation patterns of UC-PBG rectangular patch antenna can be simulated with HFSS. We attained the loss curve of backward wave and direction figure to form the radiation patterns. From the resultant figures, we know the back lobe gain of UC-PBG patch antenna is smaller than that of regular one. That makes sense in design of rectangular patch antennas.The analysis methods can be applied to the study of other types of slow-wave systems and microstrip antennas. The numerical simulation results can be considered as references in practical design at some degrees.