A Study Of Microstrip Reflectarrays And Low Profile Resonant Cavity Antennas

In recent years there has seen a rapid growth in the development of modern antennas, primarily driven by the increasing demand for the developments of modern radar, wireless communication and electronic warfare as well as the upgrading of electronic equipments. Microstrip reflectarrays and resonant cavity antennas have been drawn more and more attention and become important research topics in antenna area, because of their outstanding features such as low mass and volume, feeding simplicity, possibilities of beam shaping and control, ease of manufacture and low cost. As the main part of a research project, this dissertation is mainly concerned with the design and implementation of broadband microstrip reflectarrays and low profile resonant cavity antennas. The author's major contributions on the subject can be summarized as follows:1. As the basic of the research work, a full-wave analysis technique based on the spectral domain method of moments and Floquet modal expansions is investigated to analyze the planar periodic structures. The electric field integral equation for single layer planar periodic structure is established in the spectral domain and than solved by employing the Galerkin method to obtain the generalized scattering parameters. Multilayer periodic structures are analyzed in a very flexible and efficient way by cascading iteratively the generalized scattering matrix. Numerical experiments have been done to validate the spectral domain method of moments.2. Based on the Fabry-Perot interferometer theory, several high gain low profile resonant cavity antennas are designed and implemented. Firstly, a planar electromagnetic bandgap (EBG) surface is used as the ground plane of the resonant cavity antenna to significantly reduce the resonant cavity profile. A circularly polarized (CP) microstrip patch is then embedded into the low profile resonant cavity, generating high gain circular polarization. Finally, based on the characteristics of the high reflectivity and low reflection phase of the metamaterial superstrate, a high gain low profile resonant cavity antenna without using EBG surface as the ground is proposed.3. A subwavelength rectangular patch element is presented for designing a CP reflectarray, which converts the linearly polarized incident field of the feed into an outgoing CP field. Compared to the conventional near-resonant patch, the subwavelength one can realize a more similar behavior for the phase response curves at different frequencies, leading to broader bandwidth. Additionally, a CP reflectarray using novel subwavelength elements and the element rotation technique is designed. Since the rotation of the novel element introduces reflection phase compensation independent of the frequency, well behaved characteristics of gain and circular polarization across a wide bandwidth can be achieved for the reflectarray.4. Design methods of large reflectarray with contoured beam pattern are studied systematically. The phase-only synthesis technique based on the intersection approach is investigated to obtain the phase distribution on the reflectarray surface. In order to avoid undesired local minima, a method for generating suitable starting point is proposed. The final desirable result can be obtained by using a simple intersection approach with uniform constraint based on the starting point. Prototype of a dual-band dual-polarization reflectarray with shaped beam is fabricated, and its measured results demonstrate the validity of the design methods. In the broadband design of the large reflectarray, an approach for fixing the optimal position of the feed is clearly presented to minimize the differential spatial phase delay. Then, a modified optimization method for shaped beam reflectarray is proposed, in which the elements are optimized to match the required phase distributions for not only the central but also the extreme frequencies. Based on the aforementioned methods, a broadband large reflectarray with dual-polarization China coverage pattern for satellite communication is designed, and the simulated results demonstrate the efficiency of the design methods.