Research On Wide-angle Scan Phased Array Based On Artificial Electromagnetic Materials

In order to meet the increasing multiple function requirements of phased array radar in the aspects such as target search, threat detection, discrimination, and precision tracking, the research on wide-angle scan phased array antennas has gained increasing attention among antenna researchers. In this dissertation, we aim to improve the beam scan range of microstrip phased arrays. The idea of using artificial electromagnetic materials in the form of high impedance surfaces(HIS) as antenna ground is proposed. Novel low-profile antenna elements with bi-directional endfire radiation, broadbeam radiation, as well as wide-angle scan arrays with scan angle up to 88o(which greatly expand the scan range of traditional phased arrays) are then presented and analyzed. In addition, based on the fact that high impedance surfaces constructed by periodic subwavelength unit cells are sensitive to the polarization of the propagation waves, two kinds of surface waveguide(SWG) topologies which can support both TM- and TE-mode with the same phase velocity are proposed. The main research contents of the dissertation are summarized as follows:In chapter 1, the research background of this dissertation is presented. First, the research background of phased arrays and especially wide-angle scan arrays is introduced. Then, their development and research status are reviewed. Finally, the main work of this dissertation is summarized.In chapter 2, the unique electromagnetic characteristics of HIS gound are investigated. A novel low-profile antenna with bi-directional endfire radiation performance is proposed. An HIS is employed as its ground. The simulated and measured results demonstrate that the strong coupling between the antenna radiation element and the HIS ground plane can induce the surface-wave propagation in the HIS ground and thus reduce the specular reflection of the metallic ground plane. As a result, a unique radiation pattern that is distinct from traditional HIS-based antennas which exhibit broadside radiation is achieved.In chapter 3, the technique of reconfigurable antennas is introduced. The concept of using HIS to obtain low elevation-angle radiation of planar Yagi-Uda-like antennas is proposed. A pattern-reconfigurable wide-beam antenna based on HIS ground is then presented. The antenna exhibits a switchable broadbeam radiation pattern with main beam tilts to end-fire direction. The working principle of the HIS ground is also investigated by analyzing its dispersion diagram.In chapter 4, the idea of using both HIS and pattern-reconfigurable technique to expand the scan range of planar phased arrays is presented. First, a HIS-based, patternreconfigurable antenna element is designed and then adopted to the design of an eightelement array. With uniform magnitude and progressive phase excitation, the array performs a wide scan angle up to 88°, which successfully overcomes the challenge of limited scan range. In addition, different array antenna pattern modeling methods that include mutual coupling effects are reviewed.In chapter 5, the investigation of using HIS for wide angle scan arrays is carried out. A printed wire antenna and a phased array based on HIS ground are proposed. The radiation elements are printed wire antenna; thereby, the significance of using HIS to extend the scan range of planar phased arrays is emphasized. First, a broadbeam antenna element is designed. The simulations and measurements show that the eight-element phased array can scan from-85°to +85°in the H-plane. Meanwhile, low side lobe levels and low gain fluctuations are maintained over the whole scan range. Besides, the working principle of a HIS-based antenna is modeled and analyzed, which provides a theoretical basis for HIS-based broadbeam antenna elements and HIS-based wide-angle scan arrays.In chapter 6, two kinds of SWG topologies which can support both TM and TE modes with the same phase velocity are presented. SWGs constructed by periodic subwavelength structures share the drawback of polarization sensitivity. The first type is analyzed with the example of a loop-wire configuration and the second type is demonstrated with a modified Bow-Tie-like structure. The results verify their performance of polarization insensitiveness. Based on these two topologies, different configurations with the same polarization insensitiveness can be created. These kinds of SWGs can be applied to broadbeam antenna designs so as to achieve broadbeam patterns over the whole upper space, as well as planar wide-angle scan arrays.Finally, in chapter 7, the research of this dissertation is summarized and future research is proposed.