Terahertz Intelligent Reflection Array Metasurface For Beam Agility

The upcoming sixth Generation(6G)communication network will provide ultra-fast data transmission and ubiquitous wireless connectivity,tightly combining physical and digital information.Terahertz(THz)spectrum,with higher frequencies and wider bandwidths,offers great potential for 6G wireless technology.Reconfigurable intelligent surface(RIS)is an important development direction for future 6G communications.RIS is constructed by embedding active elements into passive metasurfaces,which is artificially designed periodic structures.In the thesis,the terahertz intelligent reflection array metasurface for beam flexibility is studied,and its multi-function beam reconfigurable characteristics are studied by combining the metasurface coding theory and the metasurface polarization regulation theory.The main research work of this thesis is as follows:1.For current polarization conversion devices,there was very little research work that can simultaneously achieve ultra-broadband,high-efficiency,and easy-to-process cell structures.In the thesis,a double L-type terahertz band polarization conversion unit is designed,which has the characteristics of high efficiency and ultra-wideband polarization conversion.The unit structure can realize the conversion of the x-polarized wave to the y-polarized wave from 0.24 THz to 0.52 THz,and the conversion efficiency in this frequency band is over 90%.2.For incident terahertz waves to be scattered in any direction of space through the metasurface structure,the RCS reduction function is realized.The polarization conversion metasurface unit and its mirror structure constitute a 1-bit coding phase shift unit,a P-type GRS coding is used,and the P-type GRS coding is superimposed with the cross-type coding and the checkerboard coding respectively through the convolution principle,two convolutional codes are generated and adopted.The experimental results show that the normalized amplitude of the two convolution coding metasurface arrays is-25 dB on average when the plane wave is incident at an oblique angle of 15°,which is about 5 dB lower than that of the P-type GRS coding metasurface array.3.Based on the research on intelligent reconfigurable metasurface in the microwave band,an intelligent reconfigurable metasurface in the terahertz band is proposed.To verify the multi-functional beam reconfigurability of the metasurface unit,the metasurface unit adopts fractional coding,block coding,convolution coding,and GRS coding,and realizes the functions of beam scanning,multi-beam reconstruction,and RCS reduction.The CST simulation results show that the coding metasurface array can achieve flexible control of double beam continuity in the range of-24°?-5° and 5°?24° in the terahertz frequency band;by using block coding and convolutional coding multi-beam reconstruction;By convolving the P-type GRS coding and the checkerboard coding,the convolutional coding array has obvious improvements in terms of the maximum reduction and the 10 dB reduction bandwidth compared with the P-type GRS coding metasurface array,in the frequency range of 115-130 GHz,the RCS value to less than15 dB when the electromagnetic wave is incident at an oblique angle of 15°.