基于微波网络理论的可重构超表面单元设计方法与性能上限分析

Design Method and Performance Limit Analysis of Reconfigurable Metasurface Element Based on Microwave Network Theory

在微波频段,应用在可重构超表面单元上的开关往往具有良好的通断性能,可以在单元层面实现低损耗、180°相位差的1-比特相位量化特性.随着频率提升到毫米波甚至太赫兹频段,开关性能会因为寄生效应而下降,引起可重构超表面单元的设计困难.在本工作中,将可重构超表面单元的等效为一个微波二端口网络模型,通过分析网络的阻抗参数和散射参数,指出了单元反射系数与开关反射系数的传递关系.所提的关系式,经过不同频段的不同开关与单元结构的仿真验证.本工作可以根据任意开关参数,给出1-bit的单元的性能上限,所提的设计流程可以指导太赫兹可重构超表面单元的设计与优化.

In the microwave frequency band,switches applied to reconfigurable metasurface units often have good on-off performance,and can achieve 1-bit phase quantization characteristics with low loss and 180°phase difference.As the frequency increases to the millimeter wave or terahertz band,the switching performance will degrade due to parasitic ef⁃fects,which makes the design of reconfigurable metasurface units difficult.In this work,the equivalent model of the recon⁃figurable metasurface unit is a microwave two-port network.By analyzing the impedance parameters and scattering param⁃eters of the network,the transfer relationship between the unit reflection coefficient and the switching reflection coefficient is pointed out.The proposed relationship is verified by simulation of different switches and unit structures in different fre⁃quency bands.This work provides the upper limit of the performance of a 1-bit unit according to arbitrary switching param⁃eters.The proposed design procedure can guide the design and optimization of terahertz reconfigurable metasurface ele⁃ment.