Study On Electromagnetic Characteristics Of Resonance-Type Microwave Photonic Crystals And Its Applications In Antennas

Photonic Crystal (PC) is a new type periodic structure which has frequency bandgaps, and the propagation of electromagnetic waves whose frequencies are within the bandgaps is forbidden. The idea of employing PBG structures was first used in the optical frequency domain. However, photonic bandgap structures not only can mimic the properties of the semiconductors in the optical range, but are also scalable to a wide range of frequencies. Because there are some advantages of factures and measures in microwave region, the research about microwave photonic crystals (MPCs) developed very rapidly in recent years. As a very important kind of MPCs, the resonance-type microwave photonic crystals have been studied in this dissertation, and the research work covers their electromagnetic characteristics and the practical applications in microwave antennas.The concept of resonance-type microwave photonic crystals is introduced for the first time in this dissertation. The mechanism of bandgap forming is investigated, and the characteristics of resonance-type MPCs which are different from Bragg-type MPCs are discussed. Some familiar resonance-type MPCs and their applications in microwave engineering are presented. The FEM and FDTD methods are chosen to analyze the eigen electromagnetic modes and the transmission parameters of the resonance-type MPCs separately. These two numerical methods are all valid for the analysis of resonance-type MPCs bandgap characteristics.As the representative of resonance-type MPCs, the electromagnetic characteristics of high impedance surface (HIS) have been studied. The effective medium model of HIS is investigated and used to explain the reason why HIS have frequency bandgaps. Using the FEM-PML and FDTD methods, the surface wave bandgaps of HIS are analyzed. Also, the bandgaps have been measured using the measurement system which constituted by common instruments. The reflection phase of HIS is computed using FDTD method, and the in-phase characteristics and the connection between the reflection phase and surface wave bandgap are obtained. From the point of view of the complex reflection coefficient, the HIS has a particular boundary condition and can be treated as artificial magnetic conductor (AMC). More than the research works above, some new type HISs are also introduced. These new HISs have special periodic elements so that they have the properties of low frequency, wideband and small configuration size.The applications of resonance-type MPCs in microwave antennas and antenna arrays are studied. The HIS has been used in simple wire antennas, microstrip antennas and waveguide aperture antennas separately. Based on the researches of antenna elements, the applications of HIS in waveguide aperture antenna arrays are also investigated, including two-element, four-element and multi-element arrays. The results show that the resonance-type MPCs can improve the characteristics of the antennas and antenna arrays. The profile of the antenna can be reduced, the gain of main lobe has addition and the radiation level of back/side lobes decrease. The resonance-type MPCs also can reduce the mutual coupling between the antenna elements or arrays because of the frequency bandgaps.Lastly, the applications of resonance-type MPCs in phased arrays have been discussed simply. The resonance-type MPCs can be used to suppress the mutual coupling between the phased array elements, and which will improve the scan characteristics of phased array through ameliorate the wide-angle impedance matching and eliminate the scan blindness.