Theory And Design Of Reflective Phase-shifting Surface For Generating Vortex Radio Waves Based On Graphene

Vortex radio waves,which have infinite numbers of mutually orthogonal orbital angular momentum modes,are deemed as a promising solution for relieving the crisis of the limited radio frequency resources,and become a potential way to widen the communication channels in radio frequency region.Nowadays,many OAM-generating antennas have been proposed,and part of them had been implemented into realize multichannel transmission via multiple OAM modes in the light-of-sight communication.However,it is still hard to see the full electromagnetic field theory analysis about the OAMgenerating antennas,and brings obstacles in both the accurate design and practical engineering for those devices.On the other hand,graphene as a new artificial nano-carbon material,prevails in the study of mircrowave devices due to its excellent characteristics in electromagnetics,thermodynamics and mechanics,etc,especially promotes the research and development of mircrowave devices in THz band.The graphene-based mircrowave devices possess many remarkable advantages,such as two-dimensional profile,small size,low lost,easy for integration.Furthermore,when combined with reflectarray,graphene can perfectly match with it since the former also has the merits that being low profile,easy for manufacture and integration.It should be noted that the graphene reflectarray can realize the reconfigurable radiation pattern via the unique electrical free degree,which is given by the tunable conductivity of graphene when biased with extra static electromagnetic field.This paper is mainly focused on the theory of reflective phase-shifting surface for generating vortex radio waves and the corresponding design of graphene reflectarray.Both the core and innovation points of this paper are listed as below:1.A theory analysis of reflective phase-shifting surface for generating vortex radio waves,including disc,ring belt and polycyclic structure.Base on this theory,it is very convenient to obtain the expressions of the OAM-carrying electromagnetic field corresponding to this kind of antenna,and provides the designer the capability of manipulating the radiation pattern and help them to achieve better design.This presence of this theory fills the blank of the full electromagnetic field analysis related with planar spiral phase plate,and it can not only implemented into the analysis of reflective phase-shifting surface but also transmission type.2.A design of the reconfigurable graphene reflectarray with tunable focus.Since the reconfigurable graphene reflectarray for generating vortex THz waves presented in the chapter 2 can not compensate the phase of incident(quasi-)spherical wave excited by practical sources,the simulated radiation pattern of this array deviates from the theoretically calculated one proposed in the chapter 3 significantly.This design defect could depreciate the value of this antenna in the engineering application.Our new design of the reconfigurable graphene reflectarray with tunable focus can provide electrical tunable ability in phase correction for the incident(quasi-)spherical wave.The full-wave simulated results demonstrate that the proposed structure can provide a dynamically controllable focus at 1.5 THz.The peak realized gain and the radiation efficiency are higher than 22 dBi and 65%,respectively,for both the short and long focuses of 3.2? and 8.0?.