| Efficient and fast beam control scheme is a key technical problem to realize high-speed terahertz wireless communication system.The terahertz composite functional sequence beam modulation metasurface proposed in this paper is an effective new way to realize planarization,digitization,diversification and rapid new scanning mechanism.Carrying out high-performance terahertz polarization control mechanism study and device development can provide theoretical basis for the development of terahertz technology.This article first analyzes the polarization of electromagnetic waves.By applying Matesurfaces in polarization control devices,it breaks through the limitations of traditional electromagnetic wave polarization control devices,and has the advantages of high polarization conversion efficiency,ultra-wideband,and high integration..On this basis,the beam deflection function is added to realize functional combination,and further expand the flexibility of beam control.The high electron mobility transistor(HEMT)is combined with the metasurface as an encoding unit,which is applied to an independently controlled 1-bit encoding metasurface to realize dynamic and flexible beam control.The main research of this article is as follows:1.Aiming at the polarization conversion efficiency,working axis ratio,polarization conversion quality and integration of current polarization control devices that still cannot meet the standards of terahertz integrated communication systems,a reflective linear-to-circular polarization is proposed.Polarization conversion unit,within the bandwidth range of 0.33-0.38 THz,the average reflection amplitude is about 0.9,the polarization conversion efficiency reaches 0.9,and the ellipse angle is about 44°,achieving a ultrabroadband linear-to-circular polarization conversion with high polarization conversion efficiency and high polarization conversion quality.The phase gradient is introduced on the basis of the generalized Snell's law.The 6 units with high polarization conversion efficiency are engineered with 60° phase gradient in x direction.In the working bandwidth of 0.34-0.37 THz,a beam deflection of 30° is achieved for perpendicularly incident electromagnetic waves,and linearly polarized waves are converted into circularly polarized waves for reflection,and a terahertz polarized deflection array with composite functions is realized.The composite functional sequence of polarization deflection based on the metasurface has great application potential in high-performance,highly integrated terahertz integrated communication systems.2.In order to meet the needs of terahertz dynamic wavefront control,two new artificial microstructure composite units based on HEMT as dynamic OOK modulation devices are proposed.To further analyze the resonance characteristics of the unit,a HEMT-metasurface composite unit surface admittance equivalent theory is proposed based on the transmission line theory.By analyzing the coupling state of the unit,the resonance frequency and reflection amplitude and phase characteristics of the unit are reconstructed.By applying an external voltage to change the two-dimensional electron gas concentration in the unit HEMT,the 180° phase shift adjustment is realized,and the reflection characteristics of the encoding unit of the 1-bit encoding metasurface are met.3.Based on the research of HEMT-metasurface composite unit,a 4*4 unit with a wavelength independently controlled is designed,which achieves a phase shifting of 180°under the condition of ideal on-off of HEMT.The bandwidth is greater than 10 GHz,and the average reflection efficiency is greater than 0.8.The composite 4*4 unit are arranged according to a specific coding sequence to form a dynamic modular coding wavefront control,which realizes multi-beam wide-angle scanning in two-dimensional and three-dimensional space.Based on the HEMT-resonant ring composite unit,an 8*8 super unit with independent wavelength control is designed,combined with the Drude dispersion model,the influence of the two-dimensional electron gas concentration on the unit's resonance state under non-ideal conditions is calculated.A smooth 360° wide-range phase shift is realized at a low switching ratio.It is determined that there are two states that can achieve a phase shift of 180° as the two units of "0" and "1" of 1-bit encoding to realize the dynamic modular encoding wavefront control device.On the basis of this research,the planar modular wavefront control device based on the HEMT-resonant ring structure was processed and tested.The experiment tested the reflection response of the unit at a voltage of 0 V to-8 V,and verified that the unit can achieve 360° smooth phase shift to meet the needs of wavefront modulation. |
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