Millimeter-wave/terahertz Low-loss Reflectarray Antenna Based On Liquid Crystal-controlled Metasurfac

With the rapid development of millimeter wave and terahertz technology,reflectarray antenna based on metasurfaces controlled by liquid crystals has attached extensive attention and research in the fields of communication,detection,and imaging because of their mature technology and low cost.Existing metasurfaces controlled by liquid crystal usually adopt the design of liquid crystal combined with metal metasurfaces.However,due to the high loss of metal in millimeter wave and terahertz band,the loss of the corresponding reflective array antenna is also high,affecting the improvement of directivity.This thesis firstly studies the reflectarray antenna based on metal metasurface controlled by liquid crystals and optimizes the phase control range and reflection coefficient of the antenna unit.Furthermore,a design of a reflectarray antenna based on the dielectric metasurface controlled by liquid crystals is proposed,which improves the reflection coefficient,reduces the antenna loss,and thus improves the antenna directivity.This antenna can be used in millimeter wave/terahertz communication and imaging systems.The main contents and innovations of this thesis are:The first part is the research on the reflectarray antenna based on metal metasurface controlled by liquid crystals.Firstly,the finite element method is used to simulate several common metal metasurface units controlled by liquid crystals.The factors affecting the reflection coefficient,phase control range,and loss are analyzed at the same time.The results show that the loss of electromagnetic waves in the metasurface units is mainly in the metal resonant structure,followed by the loss in the liquid crystals;the larger the Q value of the resonance peak of the metal metasurface unit,the larger the loss,the smaller the reflection coefficient,and the larger the phase control range.Secondly,under the condition that the phase control range is greater than 315°(a 3-bit array is realized),the geometric parameters of the metasurface units are optimized,and the maximum value of the reflection coefficient at the resonance center frequency is 0.38.After optimization,the loss coefficient corresponding to each 180° phase control is 0.35,which is 0.08 less than the loss before optimization.Finally,the optimized metasurface unit is used to arrange the reflectarray antenna working around77 GHz in a 2-bit manner,and a full-wave simulation is carried out.The directivity coefficient is about 30 d Bi,which is 10 d Bi higher than that before optimization.The second part of this thesis is the research of reflectarray antenna based on dielectric metasurface controlled by liquid crystals.First,the metal metasurface was replaced by a singlelayer dielectric metasurface,which avoided metal loss,increased the reflection coefficient at the resonance center frequency to 0.63,and achieved a phase control range of 296.9°.Further,the single-layer dielectric metasurface was replaced with a double-layer dielectric metasurface,the phase control range was increased to 320°,and the reflection coefficient at the resonance center frequency was 0.78.Finally,a one-dimensional beam scanning reflectarray antenna with an operating frequency of 72.4GHz was arranged using this metasurface unit.The 2-bit and 3-bit arrays were simulated,and the maximum beam deflection angle was 15.8°.Using the 2-bit array method,compared with the reflectarray antenna based on the metal metasurface controlled by liquid crystals,the electric field strength of the main lobe of the reflectarray antenna based on the dielectric metasurface controlled by liquid crystals is increased by 6d B,and the directivity coefficient is increased by 4.48 dBi.