A Quad Band Tunable Reconfigurable Intelligent Surface for 5G and Beyond Communications

This paper presents a 2-bit Reconfigurable Intelligent Surface (RIS) fed by an Antipodal Vivaldi Antenna (AVA) to achieve broader angular coverage and avoid feed blockage in four distinct frequency bands. The RIS consists of a 20×20 array of unit cells, each containing varactor diodes to control the reflection phase in the four operational bands. The feed antenna has a peak gain of 10.4 dBi at 8.4 GHz and -10 dB impedance bandwidth of over 10 GHz. The peak gains (sidelobe levels) of the proposed RIS at 3.5 GHz, 4.5 GHz, 5.7 GHz, and 8.4 GHz are 14.6 dBi (-29 dB), 11.2 dBi (-13 dB), 16.4 dBi (-26 dB), and 17.2 dBi (-23.7 dB), respectively. Also, at 3.5 GHz, 4.5 GHz, 5.7 GHz, and 8.4 GHz, the beam steering range (scan loss) offered by the RIS are 28° (3.9 dB), 23° (2.4 dB), 70° (3 dB), and 76° (5 dB), respectively. Overall, the RIS multiband functionality expands its potential application areas.