| The rapid development of the communication industry has made the spectrum utilization of the microwave band saturated,and it is particularly important to accelerate the research on the millimeter wave or even the terahertz band.The new generation communication system often needs to realize more functions and also has new requirements for antennas.In order to satisfy the needs of development,and make antennas have the ability to meet the changing system requirements and respond flexibly to various environments.Research on reconfigurable antennas in the millimeter wave and terahertz bands is urgent.As a new material,graphene has received great attention since its discovery due to its unique properties.It is one of the highest strength materials found till now,with good light transmission and thermal conductivity.Most importantly,it has ultra high carrier mobility,and it's conductivity can change with the applied bias voltage.This allows graphene to compensate for the inability of conventional tunable devices(PIN diodes,varactors,etc.),and to be used in the millimeter wave and terahertz bands,providing a new approach to the design of reconfigurable antennas.The main research contents of this thesis are as follows:1.Investigated the background of the subject,and studied a large number of related literatures.Introduced the research status of graphene and reconfigurable antennas at home and abroad.The characteristics of graphene and its conductivity model are expounded,which provides theoretical support for the subsequent work.2.A switchable antenna operating at 5.9 GHz is proposed.The antenna is based on a microstrip Yagi antenna,and four units are connected by a one-fourth power split.A graphene grounding structure is designed on each microstrip line.By adjusting the square resistance of graphene from 3000 ?/sq to 300 ?/sq,the antenna can switch between omnidirectional and non-radiative states.3.A millimeter wave pattern reconfigurable antenna based on Vivaldi antenna is proposed.The antenna is based on a Vivalid antenna,and the basic structure is a back-to-back structure of two antenna units,which is fed by a power split.Adjusting the square resistance of graphene,when the square resistance of two graphene sheets is 1000 ?/sq,the radiation direction of the antenna is 90° and 270°,and when one of the sheets is 1000 ?/sq and the other is 100 ?/sq,the radiation direction is 90° or 270°.The antenna is processed and tested.4.A terahertz adjustable frequency selective surface(AFSS)based on graphene-gold composite structure is proposed.The AFSS is composed of a square single layer of graphene and gold pattern.When the chemical potential of graphene is adjusted from 0 e V to 0.5 e V by applying a DC bias to the graphene,the AFSS can achieve a conversion between reflection and transmission at 1.44 THz.It lays the foundation for the design of the followup terahertz pattern reconfigurable antenna.5.A terahertz large-angle scanning pattern reconfigurable antenna is designed using the above-mentioned AFSS.The antenna consists of a tunable radome and a microstrip antenna located at the center of the radome as a radiation source.By adjusting the reflection/transmission state in each side of the radome,the antenna can radiate in six different directions covering the whole 360° range and the gain of the antenna can be adjusted.In addition,the antenna can also achieve multi-directional radiation and omnidirectional radiation. |
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