Research On Manipulation Of Electromagnetic Waves Utilizing Metasurface With Phase Discontinuities

Manipulation of electromagnetic(EM) waves is one of the most challengeable job in modern electromagnetics. Since it relies on the gradual phase changes accumulated along the transmission path, the applications of the conventional cylindrical lenses and the metamaterial lenses are limited by the thickness and the complication in terms of fabrication, and they can hardly be integrated with other components. Recently, a new methodology of controlling the propagation of EM wave has been proposed as metasurface with phase discontinuities in infrared region by introducing abrupt phase change at the interface, which provides a new solution to the construction of planar lenses. Based on metasurface with phase discontinuities, a series of microwave devices to manipulate EM waves are proposed in this theses. It is believed that the high performance of the proposed metasurfaces in the operational bandwidth and the cross-polarization conversion efficiency can lead to a wonderful prospect in relative industry.First, the mechanism of the abrupt phase changes arising from space-variant polarization modifications is investigated on the the Poincaré sphere in microwave region. The limit of the cross-polarization conversion efficiency under circularly polarized incidence are theoretically demonstrated utilizing the four-port networks for the first time in this theses.Second, a miniaturized unit cell structure for introducing abrupt phase changes at the interface is proposed and investigated in microwave region. Then, metasurface for anomalous refracetion in microwave region is proposed, simulated, fabricated and measured. The measruement results show that the anomalous refraction angle of the transmitted cross-polarized component agrees very well with the theoretical value, and the cross-polarization conversion efficiency of the proposed metasurface can reach the theoretical limit. For the first time, the microwave metasurface with high efficiency is realized.Third, we put forward the methods to optimize the operational bandwidth of the metasurface. The measured results show that the phenomenon of anomalous refraction can be observed in a broad bandwidth, in which the cross-polarization conversion efficiency keeps approaching the theoretical limit. Our design makes a remarkable progress in the cross-polarization conversion efficiency and operational bandwidth of the transmission type metasurface, beneficial to put metasurface into practical application.Fourth, two novel microwave lenes based on metasurface with phase discontinuities are proposed to manipulate EM waves. Using the abrupt phase change at the interface instead of the gradual phase changes accumulated along the transmission path, the proposed planar bi-functional metasurface can work as a diverging or converging lens determined by the helicity of the incident wave. Then an ultra-thin metasurface with phase discontinuities in two orthogonal directions is proposed to achieve the non-coplanar anomalous refraction in three-dimensional space, which makes it possible to control reflection and refraction beam with one more degree of freedom.Finally, by introducing magnetic resonance, an efficient bilayer unit cell structure which can convert the circularly polarized incidence to its cross-polarized component completely is designed. Utilizing the bilayer unit cell, the ultra-thin planar 3D convergin-diverging lens and the ultra-thin planar vorter beam plate are proposed and designed. With great improvements in efficiency and thickness reduction, the proposed metasurfaces overcome several challenges of earlier designs, providing a promising route to planarize and integrate multiple microwave components. It is believed that our research will promote the developments of the metasurface and the novel microwave devices.