A Polarization Insensitive Wideband 1-Bit RIS Unit Cell Design Using Printed Dipoles

While designing reconfigurable unit cells for Reconfigurable Intelligent Surface (RIS) applications, polarization insensitivity and oblique incidence angle stability are two of the major challenges. As practical scenarios involve incident waves with any polarization, the RIS design must have identical behaviour for any polarization. In this paper, a PIN diode loaded dipole based design is explored to implement a one bit reconfigurable unit cell. The phase difference between the ON and OFF states is close to $\mathrm{1 8 0}$ deg. Four dipoles oriented along two diagonals ensure polarization insensitive behaviour. The reflection response of metasurface unit cell changes with the variation in incidence angle. Thus, a reflection response that is stable up to a high angle of oblique incidence is desirable for RIS unit cell designs. The proposed reconfigurable unit cell has a stable oblique incidence response up to $\mathrm{4 5}$ deg for both TE and TM polarizations over a wide frequency range from 3.57 GHz to 4.38 GHz.