Abstract Reconfigurable intelligent surfaces, comprised of passive tunable elements, are emerging as an essential device for upcoming millimeter wave and terahertz wireless systems. A fundamental aspect of the device involves the tuning technology used to achieve reconfigurability. Among alternatives such as semiconductors and micro-electromechanical systems, liquid crystal offers advantages including cost- and power-effective large-panel scalability. In this context, conventional liquid crystal-based reconfigurable intelligent surface approaches face limitations in optimizing for bandwidth, response time and loss simultaneously, requiring trade-offs between them. Here we detail an architecture for a liquid crystal-based reconfigurable intelligent surface with compact defected delay lines that provide continuous, 360-degree tunability, enabling fast response time, wide bandwidth and low loss. A reconfigurable intelligent surface with a thin 4.6 μm liquid crystal layer is designed, fabricated, and characterized, exhibiting response times of 72 milliseconds, insertion losses below 7 dB, and a 6.8 GHz (10.9%) bandwidth at 62 GHz, all while utilizing a lossy glass substrate and gold as a conductor.
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