A 2-bit Polarization-Insensitive Unit Cell for Triple Band Reconfigurable Intelligent Surface

This paper presents a unit cell of reconfigurable intelligent surface (RIS) that is polarization-insensitive, tunable, and stable even for oblique incident signals in multi-frequency bands with very low absorption. A low loss substrate has been utilized to design the unit cell. The unit cell consists of a plus-shaped patch inside a square-shaped metal loop connected by four symmetrically arranged varactor diodes on the top surface and the bottom surface is covered with a metal sheet. A via is placed in the center of the unit cell connecting the top and bottom surface through the substrate. By changing the capacitance of the diodes various phase shifts in S
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has been obtained. The proposed design is simulated for the center frequencies of each frequency band (3 GHz, 5.2 GHz, and 6.2 GHz), and the results show that the design is insensitive to polarization and can cover 360° phase in 90° intervals. Phase variation remains constant up to 70° for TE and 20° for TM polarized incident signals.