Scalable mm-Wave Liquid Crystal Reconfigurable Intelligent Surfaces based on the Delay Line Architecture

TL;DR

This paper introduces a scalable, broadband liquid crystal reconfigurable intelligent surface design based on a delay line architecture, demonstrating high beam steering capability and potential for efficient, large-scale mm-wave applications.

Contribution

It presents a novel DLA-based LC-RIS architecture that enables wide bandwidth, continuous phase control, and scalability to large element counts, with experimental validation.

Findings

Beam steering over ±60° achieved

Bandwidth exceeds 9% for large apertures

Scalability demonstrated with 750-element prototype

Abstract

This paper presents the design, fabrication, and characterization of broadband liquid crystal (LC) reconfigurable intelligent surfaces (RIS) operating around 60 GHz and scaling up to 750 radiating elements. The RISs employ a delay line architecture (DLA) that decouples the phase shifting and radiating layer, enabling wide bandwidth, continuous phase control exceeding 360{\deg}, and fast response times with a micrometer-thin LC layer of 4.6 micrometer. Two prototypes with 120 and 750 elements are realized using identical unit cells and column-wise biasing. Measurements demonstrate beam steering over +-60{\deg} and -3 dB bandwidths exceeding 9% for both apertures, confirming the scalability of the proposed architecture. On top of a measured nanowatt power consumption per unit cell, aperture efficiencies above 20% are predicted by simulations. While the measured efficiencies are reduced to 9.2% and 2.6%, a detailed analysis verifies that this reduction can be attributed to technological challenges in a laboratory environment. Finally, a comprehensive comparison between the applied DLA-based LC-RIS and a conventional approach highlights the superior potential of applied architecture.