Synthesis of a robust RIS architecture with a high degree of freedom for flexible beamforming generation

This work presents a bi-layered RIS hardware architecture with a high degree of freedom for flexible biasing, which leads to dynamic beamforming. As the RIS array size increases, elementwise biasing control becomes complex. To counter this problem, A simple unit cell hardware structure integrated with a tunable varactor diode is realized for block-wise control of unit cell array elements. The bi-layered structure is synthesized using an FR4 substrate with thickness values of 1.6 and 0.8 mm and a subwavelength profile of 20x20 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> connected with shorted metal via for biasing. The proposed reflective unit cell structure resonates in the frequency range of 3.8 GHz to 4.2 GHz with discrete reflection phase values between -110<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> to -140<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> for the tunable capacitance range of 0.46-0.8 pF. The structure reflective performance is analyzed using a predefined and block wise 5x5 RIS array simulated using the CST Microwave Studio Tool. The high degree of freedom for the proposed RIS architecture is demonstrated by provisioning suitable bias voltages (-4 to -15 V range) either row-wise/column-wise unit cell block control. The features of flexible beam forming, high degree of freedom in biasing, and robustness are explained using simulated results.