2-Bit Quad Band Reconfigurable Intelligent Surface for Modern Wireless 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 is placed at an equivalent focal point of the RIS to illuminate it. The feed antenna has a peak gain of 10.4 dBi at 8.4 GHz and a -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 28º (3.9 dB), 23º (2.4 dB), 70º (3 dB), and 76º (5 dB), respectively. Overall, the RIS multiband functionality expands its potential application areas.