Liquid Crystal-Filled 60 GHz Coaxially Structured Phase Shifter Design and Simulation with Enhanced Figure of Merit by Novel Permittivity-Dependent Impedance Matching

Abstract

This work serves as the first simulation investigation to tackle the liquid crystal (LC)-filled coaxially structured continuously variable phase shifter at 60 GHz, wherein the LCs act as single tunable dielectrics fully occupying the millimeter-wave (mmW) power transmitted (i.e., free of leakage or interference). Impedance and effective dielectric constant computations are settled, followed by the quantification of the interplay between the dielectric thickness and the dielectric constant (Dk) for a controlled 50 Ω impedance. Geometry’s aspect ratio (AR) effects are exploited for the coaxially accommodating topology filled with mmW-tailored LCs with an operatable Dk range of 2.754 (isotropic state) to 3.3 (saturated bias state). In addition to the proposed structure’s noise-free advantages, a novel figure of merit (FoM) enhancement method based on Dk-selection-based impedance matching is proposed. The optimum FoM design by simulation exhibits a 0–180.19° continuously variable phase shift with a maximum insertion loss of 1.75871 dB, i.e., a simulated FoM of 102.46°/dB when the LC-filled coaxial geometry is 50 Ω and matched with the Dk of 2.8, corresponding to the dielectric thickness of 0.34876 mm and line length of 15.92 mm. The envisioned device fabrication and assembly processes are free of the conventional polyimide alignment agent and the related thermal and electrical concerns. Significant cost reduction and yield improvement can hence be envisaged. The topology can also serve as a test structure for broadband characterizations of LC materials and new electro-optical effects.

Modeling 0.3 THz Coaxial Single-Mode Phase Shifter Designs in Liquid Crystals with Constitutive Loss Quantifications

“…The work [25] also highlights the trade-offs in performance metrics compared to previously proposed planar transmission line structures such as the inverted microstrip [32] and enclosed coplanar waveguide [20] configurations. Despite the compromises in performance metrics, the fully enclosed and symmetric electromagnetic structure and the polyimide (PI)-free manufacturing process associated with the proposed LC-filled coaxial phase shifters [25] offer significant advantages over the traditional planar transmission lines as accommodating structures for LCs (requiring time-consuming and thermally stringent PI processing and a rubbing process [20] for mechanically aligning LC molecules). In electromagnetic parlance, the coaxial structure radially filled with LCs features a single-dielectric encompassed device topology that eliminates the multi-dielectric competition and interface effects (coupling and radiation) as encountered by the planar solutions, hence the coaxial approach is less susceptible to undesirable higher-order modes.…”

“…Continuous (analog) beam steering [22], however, has become feasible due to advancements in nematic liquid crystal (LC) microwave technology [23]. This entails integrating the continuously tunable anisotropic dielectric properties of LC materials [24] with microwave transmission lines [25] and components [26]. Figure 2 below outlines the scope and importance of LC-based variable phase shifters for mechanical rotation-free phased-array electronic beam-steering applications with ultra-high spatial resolutions.…”

“…At the millimeter-wave domain, our recent research efforts have introduced the first LC coaxial phase shifter at 60 GHz [25], representing a notable advancement. The work [25] also highlights the trade-offs in performance metrics compared to previously proposed planar transmission line structures such as the inverted microstrip [32] and enclosed coplanar waveguide [20] configurations.…”

“…At the millimeter-wave domain, our recent research efforts have introduced the first LC coaxial phase shifter at 60 GHz [25], representing a notable advancement. The work [25] also highlights the trade-offs in performance metrics compared to previously proposed planar transmission line structures such as the inverted microstrip [32] and enclosed coplanar waveguide [20] configurations. Despite the compromises in performance metrics, the fully enclosed and symmetric electromagnetic structure and the polyimide (PI)-free manufacturing process associated with the proposed LC-filled coaxial phase shifters [25] offer significant advantages over the traditional planar transmission lines as accommodating structures for LCs (requiring time-consuming and thermally stringent PI processing and a rubbing process [20] for mechanically aligning LC molecules).…”

“…In our pioneering work combining coaxial transmission lines with LCs [25] at 60 GHz, we achieved a phase shifter by filling the coaxial transmission line with LCs in two Over the past two decades, various demonstrations have showcased LC-enabled tunable phase shifting [20,22,23] and reconfigurable frequency filtering [27,28], exhibiting commendable performance across microwave and millimeter-wave frequency ranges, typically up to V band [20] and W band [29,30]. The state of the art in this field has also witnessed the expansion towards a wider portfolio of LC-based photonic devices, e.g., [31] on THz tunable metamaterial with LCs for modulations of phase, intensity, and polarization, leading to potential applications in THz modulators, filters, and switches.…”