Ultra-Wideband Millimeter-Wave Reconfigurable Intelligent Surface

In this paper, an ultra-wideband millimeter-wave reconfigurable intelligent surface (RIS) is presented. First, the phase responses of RIS with different resonant modes are analyzed, and an approach to extend bandwidth by incorporating the resonant structure is proposed. As the bar-shaped slot and split square slots are added to the element, the operating bandwidth is gradually enhanced. Moreover, the phase difference range of 180 ± 20° is realized from 23.8GHz to 45.6GHz (62.8%), fully covering the commercial mm-wave n257, n258, n259, n260, n261 bands. For further verification, a RIS array is designed and simulated. The main beam can be scanned from 0° to 60° at a wide frequency range. Furthermore, the simulated gain response curve of the RIS array demonstrates that the 3-dB gain bandwidth is obtained from 27GHz to 46.1GHz (52.3%).