Multi-Functional Intelligent Electromagnetic Surface Design Using Dual-Frequency Coding Modulation

With the rapid development of communication,radar and antenna technologies,reconfigurable intelligent surfaces(RIS)as a kind of electromagnetic wave control device with high controllability and programmability,are receiving increasing attention.Dualfrequency coded reconfigurable intelligent electromagnetic surface is an emerging technology and can be widely used in antenna design for 6G and wireless networks in the future.Such antennas can enhance signal transmission and reception,increase network bandwidth and data rate.Specifically,dual-frequency coded reconfigurable intelligent electromagnetic surfaces can support signal transmission and reception at multiple frequency bands simultaneously,thereby expanding network capacity and coverage.In addition,this technology can also reduce network interference and noise,and improve signal quality and reliability.6G is an entirely new communication technology that requires higher frequency bands and larger bandwidths to support faster and more stable data transmission.Dual-frequency coded reconfigurable intelligent electromagnetic surfaces can effectively increase the bandwidth and transmission rate of 6G networks,while reducing signal transmission delay and improving user experience.Based on dualfrequency coding control,this thesis explores the research and application of multifunctional intelligent electromagnetic surface technology based on dual-frequency coding.The main work of this thesis is as follows:1.This thesis introduces the theory of reflective metasurface wavefront modulation and dual-frequency operation.Specifically,the generalized Snell’s law and the transmission line theory of reflective metasurfaces are included.Metasurface wavefront modulation utilizes the miniature elements in the metasurface to adjust their phases and amplitudes,thereby modifying the wavefront distribution of the reflected wave and achieving the control over the incident wave.The dual-frequency theory is one of the focuses of this thesis and an important concept in metasurface technology.It refers to the ability of the metasurface to control electromagnetic waves at two different frequencies simultaneously.Through these theories,the fundamental principles and control methods of the metasurface can be thoroughly understood.2.This thesis introduces the implementation methods of dual-frequency encoded metasurfaces.Starting from single-polarized metasurfaces,single-layer and double-layer single-polarized dual-band metasurfaces were designed.The advantages and disadvantages of the two structures were compared.Specifically,the simulation results of the double-layer metasurface exhibited better amplitude consistency and bandwidth phase shift.The average linear amplitude was 0.2 higher than that of the single-layer dualfrequency structure,and the phase bandwidth was also wider.In the high frequency band of 0.246 to 0.281 THz,the phase shift bandwidth was 35 GHz with a phase deviation of180°±20°,while in the low frequency band of 0.165 to 0.172 THz,the phase shift bandwidth was 7 GHz with a phase deviation of 180°±20°.3.In order to achieve flexible control over the incident terahertz waves,this thesis implements dual-frequency metasurfaces based on polarization switching.By controlling the polarization direction of the metasurface through arranging HEMT transistors,multipolarized electromagnetic wave control can be realized.Through the design and optimization from double circular resonant ring polarization switching structure to cross dipole polarization switching structure,the final designed polarization switching metasurface unit structure has an average amplitude of about 0.5 at two frequency bands.In the Y-polarized low frequency band of 0.190 to 0.281 THz,the phase shift is 180°±20°with a maximum variation bandwidth of about 36 GHz.In the X-polarized high frequency band of 0.358 to 0.373 THz,the phase shift is 180°±20° with a maximum variation bandwidth of about 36 GHz.This thesis assembles cross-shaped dipole units into an array and verifies the multi-functional beam reconfiguration capability of its structure.The array units are respectively encoded with fractional coding,block coding and convolutional coding,realizing fractional coding beam scanning,multi-beam control of block coding and multi-beam control calculation of convolutional coding.Through theoretical analysis,the oblique incident angle is introduced to concentrate the energy of the reflected beam and turn it into single beam control,improving the reflection efficiency.In the beam scanning experiment of the cross-shaped dipole array,four-angle beam scanning was realized respectively at 0.35 THz high frequency point in the X polarization direction and 0.22 THz low frequency in the Y polarization direction.Experiment tested its good beam scanning performance and provided a reference for the research of electromagnetic surface structures based on dual-frequency encoding.