Characterization and Application of Dual Frequency Liquid Crystal mixtures in mm-Wave Reflectarray Cells to improve their Temporal Response

Abstract

<p>Liquid Crystal-based mm-wave spatially fed antennas with electronic reconfiguration are a promising solution at the higher frequencies required in next generation networks. However, one of the main drawbacks of the technology in these bands stems from the high reconfigurability times they present. Through this work, a relevant step towards overcoming the temporal problem by using Dual Frequency Liquid Crystals (DFLC) is presented. This paper details, for the first time, both the electromagnetic and temporal characterization of four commercially available DFLC mixtures in W-band, enabling their use in designing faster devices. To evaluate the experimental characterization, a reflectarray surface (made of 50x50 cells) specifically designed to achieve fast switching times with a sufficient phase range has been manufactured and measured. For this cell, a preliminary addressing technique based on overdriving has been used, exhibiting reconfigurability (rise and decay) times of 20 ms, one order of magnitude faster than the current state of the art of LC-based mm-wave planar devices. The measured results match the simulations, and reveal that a precisely designed biasing technique using overdrive must be used for DFLC-cells to achieve time reduction. Additionally, the benefits of this technology compared with other LC acceleration strategies in mm-wave are discussed.</p>

Liquid Crystals for Advanced Smart Devices with Microwave and Millimeter‐Wave Applications: Recent Progress for Next‐Generation Communications

“…Additionally, the formation of a polymer network inside can cause distortion in the alignment of the LC molecules, and the tunable area may be reduced due to the polymer concentration, resulting in a decrease in tunability (reduction of tunable region ). [ 82 ] Therefore, careful consideration is required when designing an RF device according to the application purpose.…”

“…Reproduced under the terms of the Creative Commons Attribution 4.0 International license (CC BY 4.0). [ 82 ] Copyright 2023, The Authors, published by. b) Schematic drawing of operation of DFLCs.…”

“…proposed a fast‐switching reflect‐array surface comprising 50 × 50 cells that use DFLC technology (Figure 10e). [ 82 ] They achieved an on‐time of 20 ms and an off‐time of 10 ms, using overdriving technique of 45 V for reflect‐arrays with a complete phase range (360°) in W‐band, while maintaining a 45 µm cell gap condition. It is remarkable that unlike LC/polymer composite technology, DFLCs have the advantage of almost no tunability reduction.…”

Architecture for sub-100 ms Liquid Crystal Reconfigurable Intelligent Surface Based on Defected Delay Lines

“…However, one crucial limitation of the RA lies in thick LC layers (10s to 100s of µm) needed for to achieve sufficient bandwidths, which lead to slow response times (10s of seconds [18]). Lately, efforts emerged to build RA implementations towards millisecond response time [19], but at the expense of considerably decreased LC tunability and increased losses. Hence, with the LC-RA method, trade-offs between bandwidth, loss, and response time are inevitable.…”