Investigations On Characteristics And Applications Of Passive Electromagnetic Periodic Structures

The research work presented in this dissertation covers both the numerical simulation of passive electromagnetic periodic structures (PEPSs) and their applications in stealth materials and microwave antennas.As the basic of the research work, theoretical model and numerical simulation method has been established for the study of PEPSs 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 method of moments (MOM) and the whole dimensional dyadic Green's functions are obtained by using spectral domain immittance approach (SDI). The [Z] matrix and [Y] matrix interpolation can accelerate the computation, and genetic algorithms can optimize the periodic structures to the aims.Using the above simulation tools, two passive electromagnetic periodic structures have been analyzed, including the resonance of frequency selective surfaces (FSSs) and the bandgap characteristics of photonic crystals (PCs). The primary work is as follows:(1) In FSSs, periodic cells with various types of geometries have been studied, including square patch, square hole, Eruselum dipole, square loop, circular loop, single split ring, double ring, etc. The effect of the cells' sizes, the microstrip parameters and the array lattice types on the resonance is studied and some new FSSs, such as compact FSSs, loaded FSSs and fractal FSSs, are provided. In addition, the cascading and the optimization of FSSs has been investigated for the designing aims.(2) The bandgap characteristics of PCs are studied, including one-dimension PCs, the PCs transmission line and multidimensional PCs, etc. As the representative of PCs, the electromagnetic characteristics of high impedance surface (HIS) have been given emphasis to. The effective medium model of HIS is investigated and used to explain the reason why HIS has frequency bandgaps.The applications of periodic structures in stealth materials have been studied. Because of the in-phase characteristics, the periodic structures can be used as artifical 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. This can provide a new direction for absorbing materials.The periodic structures have been applied in microwave antennas and antenna arrays. The HIS has been used in microstrip antennas and waveguide aperture antennas separately. The applications of the PCs covers in microstrip antennas and the AMC in an aperture coupled patch antenna have been studied too. Based on the researches of antenna elements, the applications of HIS in waveguide aperture antenna arrays are also investigated, including sixteen-element single ridged waveguide antenna array and four-element asymmetric ridged waveguide 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. Lastly, the applications of the PCs' frequency bandgaps in phased arrays to suppress the mutual coupling between the phased array elements have been discussed. The PCs can improve the scan characteristics of phased array through ameliorating the wide-angle impedance matching and eliminating the scan blindness.