Design Of Digital Programmable Metasurfaces In The Millimeter-Wave And Terahertz Frequency Bands

As the two-dimensional planar artificially-engineered electromagnetic material composed of sub-wavelength elements,metasurfaces have shown strong capability to manipulate electromagnetic waves in the whole frequency band.For digital programmable metasurfaces,the digitalized characterization and real-time programming can be realized by integrating adjustable components or materials,and then the flexible control of electromagnetic beam can be achieved,which promotes the application of programmable metasurfaces in information systems.In this paper,we focus on the regulation mechanism and design method of the programmable metasurfaces in the millimeter wave and terahertz bands,and verify the performance of beam manipulation of the designed programmable metasurfaces through theoretical analysis,numerical simulation,and experimental test.The main contents and innovations are summarized as follows:1.A W-band programmable metasurface based on varactor diode was developed.The 1-bit coding elements defined with 180~o-phase difference are obtained by introducing an electrically controlled varactor diode,and the effect of abnormal beam deflection of the metasurface with different coding sequences was certified via numerical simulation and experiment.This work extends the operating frequency of programmable metasurface to the W band.2.A terahertz programmable metasurface based on liquid crystal was studied.The 1-bit coding elements arising from different phase responses were designed by integrating liquid-crystal material with tunable dielectric constant,and then a one-dimensional electronically controlled programmable metasurface was developed.Far-field beam reflection test shows that the metasurface array has wide-angle beam scanning performance in the range of 25°to 55°.3.A 2-bit independently controlled programmable metasurface was designed.The 2-bit coding elements defined with 90~o-phase gradient were obtained by loading two PIN diodes,and the two-dimensional programmable metasurface at millimeter wave frequencies was designed by combining the amplitude formula of far-field scattering and the complex addition theorem,and hence flexible beamforming and beam manipulation in free space were attained for both the single-beam and multi-beam cases.