Liquid-Crystal-Based X-Band Reactively Loaded Reflectarray Unit Cell to Reduce Reflection Loss

• Published in: IEEE antennas and wireless propagation letters 2021-10, Vol.20 (10), p.1898-1902
• Main Authors: Kim, Hogyeom, Kim, Jongyeong, Oh, Jungsuek
• Format: Article
• Language: English
• Subjects: Analytical models; Arrays; Dynamic range; Equivalent circuits; Impedance; Input impedance; Liquid crystal (LC); Nematic crystals; Permittivity; Propagation losses; reactively loaded reflectarray unit cells (RLRUC); Reflection; Shielding; Substrates; Thickness; Unit cell; X-band reconfigurable unit cell
• ISSN: 1536-1225; 1548-5757
• DOI: 10.1109/LAWP.2021.3099818

This letter presents a novel design of a nematic liquid-crystal (LC)-based X -band reactively loaded reflectarray unit cell (RLRUC) to reduce reflection loss. The reflection loss of an LC-based reflectarray unit cell (RUC) can be reduced by increasing the thickness of the LC or the superstrate. However, in the conventional RUC, the superstrate thickness has little impact on the reflection loss due to the absence of a contribution to the actual input impedance. The reflection loss can be significantly reduced by adding an additional metallic patch onto the top of the superstrate, which serves as a reactive load. The reflection loss is analyzed by an equivalent circuit model in this letter. For the measurements, a 1 × 2 array of unit cells is introduced. Metallic vias shielding around the unit cell array is embedded into the substrates to substitute for a metallic wall. In addition, a simple bias configuration is achieved by inversely arranging the substrates. The RLRUC achieves a dynamic phase range of 240° with a reflection loss of only 1.5 dB. Compared to earlier work which reported an LC-based RUC that operated on the X -band, the proposed design achieves extremely low reflection loss.