| Metasurfaces have been increasingly applied in electromagnetic wave control fields due to their unique electromagnetic responses.In recent years,various electric control elements have been combined with metasurfaces to increase their versatility.The programmable metasurface beam splitter is a novel type of beam splitter based on a programmable metasurface.It embeds diodes in the metasurface unit structure and uses an external DC control circuit based on a microcontroller to achieve real-time,dynamic,and independent control of the unit state,thereby achieving arbitrary beam splitting.Compared with traditional beam splitters,programmable metasurface beam splitters have the advantages of freely adjustable beam splitting effects and flexible working modes,and can be widely used in multi-beam communication,military radar,astronomical telescopes,and other fields.In the future,programmable metasurface beam splitters can also be expanded to high-bit,polarization-insensitive,transmission/reflection multiplexing designs,and are expected to have a broader application prospect in the fields of communication,military,astronomical observation,and beyond.This paper systematically investigates the working principle of a programmable metasurface beam splitter.The theoretical analysis of the metasurface’s mechanism for controlling electromagnetic waves is presented,as well as the effect of diodes on the unit reflection coefficient.A highly efficient programmable metasurface beamformer operating near 8 GHz is designed.The main research contents of this paper are as follows:1.Design of a programmable unit based on PIN diodes.By embedding SMP1320-079 LF diodes into a multi-layer unit structure,a 1-bit programmable metasurface unit was designed.The equivalent circuit model of the programmable unit structure was clarified.Based on this model,the impact of various parameters on the reflectivity performance of the unit structure was deeply analyzed,and the parameters were comprehensively optimized to obtain a unit structure with a reflection phase close to 180° and a reflection amplitude exceeding 0.95 in the 7.8-8.3 GHz range.2.Based on the far-field scattering theory model and genetic algorithm,a metasurface coding design method was proposed and verified by simulation.This design method can quickly obtain the required coding sequence for beamforming effect using the excellent global search ability of the genetic algorithm and the high efficiency of the theoretical calculation model.Furthermore,one-dimensional coding was extended to two-dimensional coding to achieve efficient separation of2 to 9 beams.Simulation results showed that the designed coding reflection efficiencies were all greater than 70%,the power difference between beams was less than 5.1%,and the beamforming effect was hardly affected within the range of 0-15° deviation of the incident wave.3.Far-field testing of the metasurface beamformer.A metasurface sample was fabricated using multilayer printed circuit board technology,and a far-field testing system was analyzed and designed.Finally,experimental testing was completed in a standard microwave darkroom.The test results showed high agreement between the multi-beam separation effect and the simulation,with slightly decreased beamforming efficiency and uniformity.The test results proved that the programmable metasurface beamformer designed in this paper can achieve high-efficiency beam separation near 8 GHz and can dynamically adjust the beam in real-time during operation. |
