Research On Millimeter-wave Multifunctional Antennas Based On Metasurfaces

With the continuous development of communication technology,multi-functionalization has become a growing trend of wireless communication systems.As a key component of wireless communication systems,antennas are required to meet the needs of multi-functionalization.Based on the traditional antenna array,the phased array can realize beam scanning by introducing phase difference between adjacent elements,which is widely used in military and communication fields.The reconfigurable antenna is also part of the multifunctional antenna,whose states can be changed by RF switches.At the same time,due to the shortage of spectrum resources,the operating frequencies of modern communication,radar and other systems have gradually expanded to millimeter-wave bands.As a result,it is important to design multi-function antennas for millimeter-wave bands.As a two-dimensional metamaterial,metasurface has attracted much attention because of its unique ability to control electromagnetic waves,and is widely used in communication system components.This paper mainly studies the applications of metasurface in millimeter-wave phased arrays and reconfigurable antennas.In view of large loss and poor isolation of traditional RF switches in millimeter-wave bands,the phase transition of vanadium dioxide(VO₂)and its applications in millimeter-wave circuits and antennas are also studied.The main contents are as follows:1.Analysis of basic characteristics of metasurface structures and the feeding methods of metasurface antennas.The in-phase reflection characteristic of the metasurface structure is analyzed at first.Then the metasurface structure is used as the radiation element of the antenna.Three feeding methods are applied,which are slot coupling with microstrip excitation,slot coupling with CPW excitation,and microstrip coupling.Based on these feeding methods,a series of low-profile metasurface antennas are realized.2.Researches of the millimeter-wave metasurface phased array for 5G communication.Based on LTCC process,three types of feeding methods are studied,including asymmetric microstrip line feeding,double-layer strip line feeding,and double-layer slot-coupling in order to design a broadband low-profile dual-polarization metasurface antenna units.The double-layer slot-coupled feeding method is finally applied to realize a millimeter-wave dual-polarization metasurface antenna with high isolation.In response to the requirement of beam scanning for 5G communication,the metasurface antenna unit is formed into a 4×4 array.For the first time,a dual-polarized metasurface antenna is applied to a phased array,and a scanning angle of±50°is realized.3.Researches of the phase transition of vanadium dioxide thin film and its applications in millimeter-wave transmission lines.The phase transition mechanism of VO₂ thin film is analyzed at first.Then the methods to excite the phase transition of VO₂ thin film is studied,including thermal excitation,electrical excitation,and thermal+electrical excitation.The effect of each method is analyzed and compared with each other.Based on the analysis and researches above,the VO₂ thin film is integrated into transmission lines.With simulation and measurements,the transmission characteristics and parasitic effects of the VO₂ film in the microwave/millimeter-wave band are analyzed.4.Researches of design methods of millimeter-wave frequency-reconfigurable metasurface antenna based on vanadium dioxide thin film is studied.From the perspective of equivalent circuits,the resonance property of the coplanar compact metasurface structure(UC-PBG)is analyzed.By integrating VO₂ thin film,a frequency-reconfigurable metasurface structure is realized.A novel millimeter-wave frequency reconfigurable metasurface antenna based on the phase transition of VO₂ thin film is proposed for the first time.This antenna is fed by a ridge waveguide and the electromagnetic wave is coupled by two parallel slots in order to excite the antenna.Thermal+electrical excitation is used to induce the phase change of VO₂thin film.Finally,a millimeter-wave frequency-reconfigurable antenna is realized,which provides technical references for the reconfigurability of modern wireless communication/radar system antennas and other devices.