Impedance Regulation Of Graphene-Based Materials And Its Applications In Microwave Devices And Antennas

The future wireless communications system requires being highly integrated and intelligent,therefore the device performance should be greatly improved,especially microwave devices and antennas.The requirements of high performance RF Front-end such as tunable microwave devices and antennas are becoming increasingly stringent.Microwave wave devices and antennas with the characteristics of controllable and multifunctional are expected to become the core components of wireless communication system.They will play an important role in military and civil communication fields.Although the potential of traditional electromagnetic materials and structures has been fully tapped,but it still cannot meet the requirements of intelligent RF terminals.It is urgent to study the theoretical system and design method of functional devices based on new electromagnetic materials,which brings new opportunities for the development of the future wireless communications systems.Graphene is a two-dimensional carbon-based material,which has excellent characteristics.The characteristics of high carrier mobility,high transparency,high thermal conductivity,good mechanical flexibility,and dynamically tunable conductivity are widely used in the design of THz modulators,perfect absorbers,wireless sensors and new THz antennas.The discovery of graphene not only provides a new material for the design of highly sensitive electromagnetic devices,but also provides a new choice for the design of reconfigurable microwave devices.However,the application of graphene in microwave field is greatly limited due to the imperfection of the material preparation process,impedance regulation method and design theory of graphene based devices.Many excellent properties of graphene have not been explored and many basic problems have not been studied deeply,which limit its application in high-performance microwave devices and antennas.This dissertation aims to deeply explore the impedance regulation characteristics of various graphene-based materials(single,few and multilayer graphene,etc.).Then the research on graphene based microwave devices and antennas with the advantages of intelligent regulation,functional integration and good performance can be carried out according to the impedance characteristics and performance advantages of different graphene based materials.So,the main research contents of this dissertation can be summarized as follows:1.The preparation methods and impedance characteristics of different graphene based materials are systematically analyzed.The electromagnetic modeling and simulation methods of each material are studied.Through the test and characterization of different graphene based materials,the preparation process,impedance characteristics and application potential of these materials are compared and analyzed,which laid a solid foundation for the subsequent design of graphene based microwave devices and antennas in this dissertation.2.Combined the controllable impedance and electromagnetic absorption characteristics of graphene with the easy loading characteristic of microstrip resonator,a dynamically tunable filtering attenuator are realized by loading graphene sandwich structure on the cascade resonators.In order to solve the problem of poor selectivity of the proposed attenuator,a half-mode substrate integrated waveguide coupling structure is introduced to reduce the influence of graphene on the quality factor of the resonator,which can achieve high selectivity and dynamic tunability.Furthermore,the performance of the highly selective filtering attenuator is improved and the function is optimized by zero coupling technology,stepped impedance technology and varying-diode loading technology.3.Establish the transmission circuit model and resonant mode analysis method of GSS loaded microstrip dual-mode resonator.Based on the calculation of odd-even mode transmission circuit model and the full-wave simulation results of three-dimensional electromagnetic structure,the resonant characteristics and the influence mechanism of loading position of several graphene loaded microstrip dual-mode resonators are studied.Based on the characteristics of different graphene-loaded dual-mode resonators,four kinds of multifunctional integrated tunable filtering attenuators are proposed and designed,which can not only highlight the resonant characteristics of each graphene-loaded dual-mode resonator but also further improve the functional diversity of the filtering attenuator.4.In order to facilitate the application of graphene based materials in microwave reconfigurable antennas,a power distribution method and a phase control method for transmission network loaded by graphene nanoplates are proposed.A multi-channel power divider with controllable power ratio and a phase shifter with tunable output phase are designed by taking advantage of small size and wide impedance control range of graphene nanoplates.Based on this,a graphene-based millimeter wave pattern reconfigurable Vivaldi antenna and a frequency reconfigurable Loop antenna are designed,which can achieve bidirectional beam reconfigurable and improve the radiation efficiency of frequency reconfigurable antenna respectively5.A high conductivity preparation process and characterization method for multilayer graphene films is developed.A terminal microstrip antenna and a millimeter-wave multi-beam array antenna based on high conductivity multilayer graphene are designed.A method for fabrication and electromagnetic characterization of multilayer graphene array antenna is proposed,and a metal based substrate integrated waveguide Butler matrix multiport feed network is used for the design and measure of the multi-beam array antenna.The experiment results show that the multi-beam array antenna based on high conductivity multilayer graphene has the advantages of wide impedance band,light weight and low side lobe.