Electromagnetic Characteristics Of Microwave Photonic Crystals And Applications

Photonic crystals or photonic bandgap (PBG) structures are periodic metal-dielectric material with a frequency bandgap. PBG structures have been extensively studied since the concept came into being in the end of 1980's. The research work of PBG, structures in microwave region progresses rapidly because of the advantage in fabrication and measurement. The research work presented in this dissertation covers both the numerical and experimental understanding of PBG materials and their applications.First one-dimensional PBG microwave transmission line is studied. PBG material is filled into the rectangular metal waveguide and a stop band is obtained. When defect is introduced, a resonant mode appears in the stop band. Major work is on microstrip line. The defected ground structure (DGS) has been studied and a broad stop band is realized using cascade technology. Fractal structure is introduced into DGS for the aim of dual-stopband or multi-stopband characteristics. A novel structure with defected stripline is proposed to overcome the problem in encapsulation. A novel PBG coplanar waveguide is proposed for MMIC intention.PBG structures based on microstrip substrate are mostly noticed, and here the periodicity of PBG structure is in two directions. When considering PBG structure on microstrip substrate, full 3-D analytical model is build and the infinite periodic structure is reduced to one single cell by applying Floquet theorem. The numerical simulations are performed using periodic Green's functions plus method of moments (MoM) and the dyadic Green's functions are obtained by using spectral domain immittance approach. Anontrivial solution of algebraic equations requires the matrix determinant to be zero, which results in a characteristic equation. Then the bandgap structure can be solved from the roots of this equation. The bandgap characteristics of several kinds of PBG structures are calculated using this numerical tool. One is dielectric type of PBG structure, the substrate thickness and the ground plane are included in the full 3-dimensional analytical model and the air hole or dielectric block is replaced with equivalent displacement current. The results are much more accurate compared to that using simplified 2-dimension model. Another is metal-dielectric planar PBG structure, periodic elements with various geometry shape are studied, including cross dipole, Eruselum dipole, square patch, various ring structures. In addition, PBG structure with a dielectric cove layer is studied, too.A mushroom type of PBG structure has attracted mush attention because of its in-phase reflection and surface-wave bandgap. In this dissertation, this PBG structure is comprehensively studied. The bandgap structure is calculated using periodic method of moment, and the plane wave reflection phase is calculated using FDTD. An effective medium model is set up and establishes a relation between structure parameters and the lumped elements. Improvement is made to this model and the accuracy is increased. Based on this model, several novel PBG structures are proposed to obtain more compact size, which will be more fit for practical applications.The foreground of PBG structure is very attractive. The applications of PBG structures in microwave antennas are studied. One part is microstrip antenna. The effect of PBG structure to the characteristics of microstrip antenna is analyzed and the common rules are obtained in designing PBG microstrip antennas. Aperture coupled patch antenna and satellite receiving antenna are practically designed using PBG materials. Another part is waveguide aperture antennas, and their performance is improved using PBG materials.PBG structure is also adopted in antenna array. First PBG structure is used in a two-element microstrip array antenna, and the coupling is decreased. PBG structure is also used in infinite phased arrays of printed dipoles and rectangular microstrip patches. Array structure is presented and scanning characteristics have been calculated. The results show that the scan blindness is eliminated.