Electromagnetic Simulation Results of the Varactor-based Reconfigurable Intelligent Surface

Reconfigurable Intelligent Surfaces (RIS) are passive antenna arrays capable of dynamicallymodifying their reflective properties to adapt to variations in the communication channel by adjustingthe reflection coefficient of each unit cell. RIS technology has attracted significant attention for itspotential to enhance wireless communication systems, with envisioned applications in smart cities, indoorenvironments, and 5G\/6G networks, enabling more reliable and adaptive communications. This paperpresents the design, simulation, implementation, and validation of an RIS operating at 9.6 GHz, composedof a 40\u00d740 array of unit cells, where reconfiguration is achieved using Barium Strontium Titanate(BST) varactors in combination with a clustering strategy that groups five unit cells under a singlecontrol element. This approach reduces the number of independent finite elements and control lines by80%, with a quantified worst-case performance loss of 1.72 dB. As a first step, material properties andphysical phenomena such as mutual coupling between adjacent unit cells and surface edge effects wereinvestigated through full-wave simulations. Additionally, the S-parameters of the varactor models wereincorporated into the simulations to apply programmable phase shifts across the surface, while statisticalvariations due to component tolerances were also considered to model realistic performance degradation.The designed surface was subsequently fabricated and experimentally validated, demonstrating strongcorrelation between measured and simulated results. A comparison between the deactivated and activatedstates of the RIS shows a reflection gain improvement exceeding 20 dB across the angular range from20\u00b0 to 80\u00b0. Finally, the proposed RIS was thoroughly evaluated through both electromagnetic simulationsand comparisons with idealized theoretical models, offering valuable insights into practical performancedegradation and reinforcing the importance of comprehensive performance evaluations under real-worldhardware constraints.