Waveguide-Thru Closed-Form Characterization of Anisotropic Polymer Network Liquid-Crystal for mmWave Reconfigurable RF Devices

• Published in: IEEE transactions on antennas and propagation 2024-07, Vol.72 (7), p.5447-5457
• Main Authors: Kim, Hogyeom, Lee, Jae-Won, Wang, Junkai, Kim, Min-Seok, Kim, Hak-Rin, Oh, Jungsuek
• Format: Article
• Language: English
• Subjects: Anisotropic magnetoresistance; Closed form solutions; Complex permittivity; Doping; Dynamic switching time; Equivalent circuits; Exact solutions; liquid crystal (LC); Liquid crystals; Millimeter wave communication; Millimeter waves; Nematic crystals; Optical switches; Parameter modification; Permittivity; polymer network liquid crystal (PNLC); Polymers; Radio frequency; reactive mesogen; Reconfiguration; Tensors; Waveguides
• ISSN: 0018-926X; 1558-2221
• DOI: 10.1109/TAP.2024.3403939

In this article, closed-form characterization of anisotropic polymer network liquid-crystal (PNLC) for reconfigurable RF devices at the millimeter-wave (mmWave) band is achieved. For the first time, the complex permittivity of the PNLC has been extracted for various doping conditions of reactive mesogen used in the polymer network at the mmWave band. Anisotropic constitutive parameters at the two extreme states of the PNLC can be obtained through a waveguide (WG). A 1 \times 2 reflectarray simple cell in the WG enables the establishment of an equivalent circuit (EQ) for an infinite cell array, providing exact modeling for de-embedding. The PNLC has an attractive property compared with pristine nematic liquid crystals (NLCs) owing to its significantly enhanced dynamic switching characteristics. In the mmWave band, the physical cell gap of the liquid crystal (LC) inevitably increases to achieve RF performance, resulting in slow dynamic speed. However, studies on the characterization of PNLCs at the mmWave band are limited, and their evaluation methodologies are inaccurate. The fabricated cell requires no biasing circuit to achieve two extreme phase states, owing to its prealigned layer. With the proposed novel method, constitutive parameters of other LC types, modified by doping approaches for RF performance can be precisely extracted and predicted.