Bandgap Characteristics Of Microwave Photonic Crystal And Its Application In Antenna

Microwave photonic crystals (MPC), also referred as electromagnetic bandgap(EBG) materials, are periodic structures characterized by the existence of frequency bandgaps. The dissertation focuses on the electromagnetic characteristics and its application in microwave antenna.At first we establish theoretical model and numerical simulation method that are constructed in the microstrip structures. 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 the method of moments (MOM) and the whole dimensional dyadic Green's functions are obtained by using spectral domain immittance approach (SDI).Using the above simulation tools, several kind MPC structures have been analyzed, including the planar MPC and the bandgap characteristics of MPC with a cover layer. The primary work is as follows:(1) In planar MPC, the cells with square patches have been mainly studied. Some parameters which can affect the resonant performance of the MPC have been studied, including cell size, gap width, thickness and dieletric constant of substrate and that of cover layer, and radius of via. Some new MPCs, such as interdigital MPC, and spiral MPC, are provided.(2) Aimed at the dual/multiple bandgap in some antenna system design, 2-D metal cylinder EBG structure with fractal characteristics is computed and dual frequency bandgap even new complete bandgap are obtained. At last the relationship between their working characteristics and the fractal structure is summarized(3) The photonic crystals (PC) have been applied in microwave antennas and antenna arrays. The high impedance surface (HIS) has been mainly used in waveguide slot antennas including waveguide end-slot antenna, sixteen-element single ridged waveguide slotted antenna array and sixteen-element asymmetric single ridged waveguide slotted antenna array. The results show that the PCs can improve the characteristics of antennas and antenna arrays. The gain of main lobe has addition, the radiation levels of back/side lobes decrease and the mutual coupling between the antenna elements or arrays can be reduced. The application of the HIS in phased arrays is investigated basically. The HIS is used to suppress the mutual coupling between the phased array elements and the results show that the HIS can improve the scan characteristics of phased array through ameliorating the wide-angle impedance matching and eliminating the scan blindness.Isolation of receiver-radiation antenna arrays in Continuous-Wave Radar is an important parameter. In the practical design of Continuous-Wave Radar, the space between receive and radiation antenna should not be too large and not be too small,either. If the space is too small, there is a problem that the power from radiation antenna will radiate directly into receive antenna. The application of EBG bandgap can solve this problem effectively. By using EBG can reduce the mutual coupling and promote the isolation. The measured results show that the mutual-coupling coefficient reduced 15dB, improved the detective ability of Continuous-Wave Radar.(4) The applications of PC in absorbing materials have been studied. Because of the in-phase characteristics, the periodic structures can be used as artificial magnetic conductor (AMC) and substituted for the spacer of the traditional electric Salisbury screen in order to reduce the entire thickness and preserve the stability of the traditional electric Salisbury screen. The new absorbing materials which are made of PC are successfully used in waveguide end-slot antenna and asymmetry single ridged waveguide slotted antenna array. The testing results suggest that the new absorbing material can obviously reduced the Radar Cross Section (RCS) with little attenuation of these antennas' gain.