Research On New Technologies Of Wavefront Manipulation And Antennas Based On Metasurfaces

In recent years,metasurfaces,2D metamaterials with compact planar configurations,have been well studied.They have advantages of low loss,thin and compact structure,wideband operation,design flexibility,readily fabricated etc.Through effective control of electromagnetic(EM)wave amplitude,phase,polarization,etc.,metasurfaces can realize functionalities of negative refraction/ reflection,polarization conversion,focused imaging,complex beams,etc.They have been proposed for many applications such as antenna technology,holographic imaging,electromagnetic stealth,etc.The main research contents and innovations are presented as follows:First,with the challenge of the complex design,high cost,bulk,fabrication difficulties of “perfect stealth” cloaks,according to the phenomenon of abnormal refraction realized by phase gradient metasurface,a transmissive EM cloak based on phase gradient metasurfaces is designed.Initially,a gradient phase metasurface with high transmission efficiency in the Ka and Ku bands were designed to verify the generalized Snell’s law.Based on this,two transmissive invisible cloaks were designed respectively at Ka and Ku bands.Planewaves are used to illuminate them to verify their performance.Simulation results show that the wavefront distortion caused by the metal object is significantly improved by the proposed cloaking device.The stealth of the metal object with a diamond shape is realized.Compared with most "perfect stealth" cloaks,this scheme has a simple structure,easy assembly,and low cost.It can be applied to different frequency bands and other concealed objects of any shape.Secondly,with the application of the polarization conversion metasurface,we proposed a structure which is suitable for single/dual circularly-polarized(CP)antennas.The reflective metasurface with the orthogonal polarization conversion is used as the reflective ground of the linearly-polarized(LP)dipole,so that the polarization of radiation waves above the dipole is orthogonal to that of the reflected waves from the ground metasurface.The height and reflection phase are optimized in order to generate broadband CP waves.The experimental results of the prototypes show that the single circularly polarized antenna can achieve a 3-d B axial ratio bandwidth of8.0% and a peak gain of 8.03 d Bi.Taking into account the polarization diversity,the dual CP antenna is designed,which can switch the polarizations between two ports.The port isolation is greater than 20 d B.The measured results show that when it radiates left-hand circularly-polarized(LHCP)waves,the axial ratio bandwidth is 12.7% and the peak gain is 8.49 d Bi;When it radiates right-hand circularly-polarized(RHCP)waves,the axial ratio bandwidth is 7.1% and the peak gain is 7.03 d Bi.The proposed antenna can be used to form an array to improve the gain.It can be a potential candidate for high-gain CP applications.Finally,with the control of the EM wave amplitude and phase by metasurfaces,highgain low-sidelobe transmitarray(TA)and reflectarray(RA)antennas are successfully designed.A transmissive metasurface with individually controllable amplitude and phase is developed.Combined with the phase compensation method and the antenna array theory of Taylor synthesis method,the phase and amplitude distributions on the array aperture are designed respectively to achieve high-gain focusing and low sidelobe level(SLL).The simulation results of the TA show that the peak gain at 12.5 GHz is21.2 d Bi,the maximum aperture efficiency is 42%,and the SLL of the E-plane and Hplane are lower than-28 d B and-27 d B respectively,which is about 5.5 d B reduction comparing to the TA with phase compensation only.Certainly,there is a slight gain loss.Taking into account the reflection structure and high-frequency applications,a Ka-band RA with a beam direction of-20° is designed.The simulation results show that it achieves a peak gain of 26.2 d Bi at 29 GHz and a maximum aperture efficiency of 24.6%.The SLL are lower than-30.1 d B and-27.8 d B respectively.This solution has the advantages of high gain,low sidelobe,and low cross-polarization.It is suitable for planar antenna array applications in different frequency bands and beam scanning situations.