Novel Electromagnetic Metasurface Based Antennas

The continuous development of modern wireless communication systems has put forward more and more stringent requirements for the electrical specifications of antennas.Electromagnetic meta-surfaces have been capable of controlling electromagnetic wave and realizing polarization conversion,and been applied to Fabry-P'erot(FP)resonant cavity antennas,Cassegrain antennas and folded transmitarray antennas to achieve wavefront control,directional control and polarization control.These designs have received extensive attentions from researchers and have gradually become the research focus in the field of antennas.Supported by National Natural Science Foundation of China,the dissertation studies on the novel electromagnetic metasurface based antennas.The specific research contributions of the dissertation are as follows:1.A spatial angular filtering meta-surface is introduced into the design of the FP resonant cavity antenna for the dual-beam frequency-scanning performance.Asymmetrical unit cells printed on the meta-surface enable the radiation energy to move in different directions as the frequency changes,and the released emissions,meanwhile,are split into dual-beams from the initial pencil beam.We continue to implement a slot-coupled array antenna to provide excitation with the aim of achieving scanned beams in another dimension,and the proposed design ultimately demonstrates a two-dimensional dual-beam scanning performance with42°and 9°scanning angles respectively in two dimensions of the coordinate system over a frequency range from 10.50 GHz–11.25 GHz.The proposed technique,by integrating a spatial angular filtering meta-surface with a slot-coupled array antenna to generate steerable beams,should offer an efficient way to fulfill FP resonant cavity antenna with reconfigurable radiation.2.A beam-splitting meta-surface with efficient linear-to-circular polarization conversion is proposed and applied to the design of the FP resonant cavity antenna for generating two circularly polarized(CP)beams with opposite helicities.The beam-splitting meta-surface consists of a top gradient meta-surface and a bottom periodic meta-surface connected by the metallic vias through central holes in the intermediate defected metallic partition.Such a beam-splitting meta-surface based FP resonant cavity antenna would be capable of transforming the linearly polarized waves from the feed into highly directive split left-hand CP and right-hand CP waves.Especially,the present design can readily be applied to the dual vortex beam generations with dual CP characteristics,fulfilling the control of spin and orbital angular momentums of electromagnetic fields at the same time.The proposed technique,integrating the beam-splitting meta-surface into the FP resonant cavity antennas to generate well collimated split beams with linear-to-circular polarization conversion simultaneously,should offer an efficient way to build up more advanced FP resonant cavity antennas with specific radiating characteristics using functional meta-surfaces.3.As opposed to the conventional Cassegrain antenna,we introduce a meta-surface lens into the design of the Cassegrain antenna as the primary component with the combination of a secondary metamirror.The electromagnetic fields reflected by the secondary metamirror would directly transmit through the meta-surface lens,thus can remove the blockage effects from the secondary metamirror and generate well collimated beams with low sidelobes compared with the traditional Cassegrain antenna.Especially,such a Cassegrain antenna also demonstrates the perfect capabilities of synthesizing the steerable beams and splitting beams when the meta-surface lens is equipped with properly prescribed phase distributions.Finally,we fabricate the proposed meta-surface lens based Cassegrain antenna and experimentally demonstrate the functionalities of generating highly directive radiations with beam scanning and beam splitting.4.Polarization-regulated meta-surfaces capable of simultaneously controlling polarization states and wave-fronts of electromagnetic fields are applied to the design of Cassegrain antenna for the synthesis of high directivity beam.Electromagnetic fields reflected by the secondary meta-surface with tailored diverged wave-fronts would be collimated by the primary meta-surface into high directivity beam with transformed polarization states that can directly go through the secondary meta-surface without any blockage.Such a Cassegrain antenna can possess much more compact configuration by properly devising the phase distribution over the secondary meta-surface,and can also achieve high-purity polarized radiations when we enlarge the secondary meta-surface as a radome.The present approach of integrating two polarization-regulated meta-surfaces into the design of Cassegrain antenna for the generation of high directivity beam should pave the way for building up more advanced meta-surface based architectures with specific characteristics.5.A vortex meta-surface lens is designed and applied to the folded transmitarray(TA)antenna for generating well converged orbital angular momentum(OAM)vortex waves with tailored spin angular momentum(SAM).The co-linearly polarized(LP)waves from the feed would be reflected by the vortex meta-surface lens at the first place and then twisted into the cross-LP counterparts by the polarization conversion meta-surface so as to penetrate the vortex meta-surface lens for the perfect synthesis of OAM vortex beams while performing the linear-to-circular polarization conversion.The folded TA antenna can achieve ultra-low profile with a quarter of the focal length of the vortex meta-surface lens when we impose proper phase distributions over the polarization conversion meta-surface.In addition,such a compact design can readily be extended to the generation of multiple circularly polarized OAM vortex waves possessing different modes and should thus pave the way for building up more efficient wireless communication systems with greatly expanded channel capacity.