Research And Design Of Programmable Metasurfaces For Beam Scanning

Reflective metasurfaces can efficiently achieve precise beamforming.Such metasurfaces typically consist of a specific number of units with pre-designed phase distributions without the complex and expensive feed networks.However,it is worth noting that the functions of these passive metasurfaces are fixed after the fabrication of the device,even if the external electromagnetic environment changes,the function of passive metasurfaces will not change.Many of wireless applications,such as satellite communications,millimeter-wave imaging,etc.,place many demands on beam-steerable antenna systems,including reduced size,cost,and power consumption.Programmable metasurfaces have recently attracted considerable research interest because they can be reconfigured in real time to change the electromagnetic properties of metasurface units and ultimately the electromagnetic responses of metasurfaces.This reconfigurability can be achieved through changes in external conditions such as voltage,mechanical,and temperature.Among them,electronically tunable metasurfaces have received much attention from researchers because they can be fabricated at low cost using semiconductor technologies and can be rapidly switched to adapt to changing wireless channels.Electronically tunable metasurfaces are realized by loading electronically tunable lumped elements such as varactor diodes,PIN(Positive-Intrinsic-Negative)diodes,and micro-electromechanical systems(MEMS)switches within the metasurface unit.By controlling the phase distribution of the metasurface,functions such as beam scanning can be realized.Electronically tuned programmable metasurfaces are lightweight and can achieve fast and versatile beam scanning without mechanical scanning,which is the main direction development of metasurfaces in the future.The main research contents of this paper are summarized as follows:1.The research background and significance of programmable metasurfaces are mainly analyzed,and the development history of metasurfaces is briefly reviewed.According to the commonly used reconfigurable technologies,three kinds of reconfigurable metasurfaces based on materials tuning,electronic tuning,and mechanical tuning are mainly introduced.The coding metasurfaces and programmable metasurfaces are also introduced in detail,which provide more guidelines for the design of programmable metasurfaces in this paper.The related knowledge of the spatial electromagnetic control theory of metasurfaces is described in detail.The generalized Snell reflection theorem and the refraction theorem are briefly introduced,the principle of the beam scanning function realized by the reflective metasurface is deduced in detail,and the advantages and disadvantages of several reconfigurable technologies are compared and analyzed.These contents lay a solid theoretical foundation for the design and testing of reflective programmable metasurfaces.2.According to the principle of programmable metasurface,a 1-bit reflective programmable metasurface is designed by loading PIN diodes on the unit.First,combining the design method of stacked units and the way of loading PIN diodes,a relatively simple design idea of metasurface units is proposed.By controlling the on and off states of the PIN diode loaded on the metasurface unit,the unit can obtain a phase difference of 180° between the two states,and the unit amplitude is greater than-1.5d B.Finally,according to the designed metasurface unit,a 16×16 1-bit programmable metasurface operating in the Ka-band is designed,and each unit of the metasurface can be individually regulated by an external circuit.The design also comprehensively considers the phase compensation of the feed horn,and changes the phase distribution of the metasurface to realize the 2-D beam scanning function.Simulation results show that the proposed metasurface can achieve beam scanning in the range of ±60°.3.On the basis of the above work,a control circuit is designed to control the state of each unit of the programmable metasurface.From chip selection to hardware implementation and software programming control,the design and function implementation of the external control circuit of the programmable metasurface are briefly introduced.The control circuit is mainly composed of a microcontroller unit(MCU)and 32 8-bit shift registers,and a light-emitting diode is configured for each unit to represent the state of the unit.Finally,the programmable metasurface and its control circuit are fabricated by printed circuit board technology,and the experimental environment is set up to test the performance of the beam scanning of the metasurface.The experimental results verify the simulation results well,and analyzes the reasons for the differences between the simulation and the experiment.4.The Spice model is simulated for the PIN diode and the diode S-parameters in the Wband are extracted for the unit simulation design.On this basis,a programmable metasurface that operates in the W-band and can be individually controlled for each column is designed.Each unit uses two PIN diodes to adjust the state of the unit,and a large-angle beam scanning function can be achieved by changing the state of each column of units.The simulation results show that the metasurface can achieve large-angle beam scanning in the range of ±60°.