Comparison of Compact Liquid Crystal-based Phase Shifting Topologies for Reconfigurable Intelligent Surfaces

Abstract

<p>This paper presents and compares two promising approaches for realizing liquid crystal (LC)-based phase shifting topologies for Reconfigurable Intelligent Surfaces (RIS). Main requirements for the phase shifters include high Figure of Merit (FoM), compact size, low response times and constant group delay. The first approach is based on defective ground structure inverted microstrip lines (DGS-IMSL) and shows high FoM above 74 °/dB between 25 and 30 GHz. In addition, it promises low response times due to its thin 4.6 µm LC layer and features moderate physical length below 0.45 λ0. However, it is limited by a non-constant group delay. The second approach, the bandpass inverted microstrip line (BP-IMSL), has a lower FoM of approximately 26 °/dB between 28 to 30 GHz with a thicker LC layer of 20 µm. Nevertheless, a shorter physical size below 0.25 λ0 is accomplished and potential for a flat group delay is given. </p>

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

“…With the DGS-IMSL approach, a thin LC layer can be realized with low loss compared to a conventional IMSL, as metallic loss becomes independent of layer thickness. For example, a DGS-IMSL with t LC = 4.6 µm can be realized with a fraction of only 38% loss compared to a t LC = 20 µm IMSL delay line [23]. As illustrated in (f), the presented tunable delay line achieves a high FoM (see Methods) up to 81 • /dB between 57 and 63 GHz.…”

“…Polarization: In this contribution, a single polarized RIS is presented. Nonetheless, the proposed architecture also enables dual polarized RISs, for example by making use of other phase shifting topologies, such as bandpass-based delay lines [23].…”