A Modified 1-Bit Unit-Cell for mmWave RIS Optimized at Extreme Incident Angle

This paper presents a modified wideband reflective unit-cell for Reconfigurable Intelligent Surface (RIS) operating at millimeter-wave (mmWave) n257 band. The unit cell is specifically optimized at extreme incident angles and utilizes dual-polarization reflection with p-i-n diodes for a 1-bit RIS control. The design exhibits superior reflective phase difference close to 180° across most of the 3 GHz bandwidth (26.50-29.45 GHz) and reflects over 74% of the energy even at extreme angle of incidence as high as 70° from the RIS boresight. The enhanced reflectivity minimizes losses, and precise phase control improves beam pointing accuracy crucial for low-complexity 1-bit RIS. Full-wave electromagnetic simulations confirm effective performance. The unit cell is compared with the current state-of-the-art unit cells, in terms of bandwidth, polarization, phase accuracy and operation in extreme angles of incidence.