A STAR-RIS With Independent 1-Bit Wave Control

In this paper, a simultaneously transmitting and reflecting (STAR) reconfigurable intelligent surface (RIS) is proposed. This RIS comprises six metallic layers, including the top and bottom patches, two ground layers, and two middle layers with a reflective-type phase-shift circuit and bias circuit. Two pairs of p-i-n diodes are used to independently control the phases of the reflection and transmission. The reflective-type phase shift circuit consists of a branch-line coupler, with two of its ports each connected to a one-eighth wavelength open circuit stub via a p-i-n diode. Another pair of p-i-n diodes is used in the bottom patch to control the phase of transmitted waves. 1-bit reconfigurable transmission and 1-bit reconfigurable reflection is achieved in this design. A unit cell is designed at 10 GHz and a 180-degree phase difference is simultaneously and independently obtained for reflection and transmission according to the simulation results.