Liquid-crystal-based floating-electrode-free coplanar waveguide phase shifter with an additional liquid-crystal layer for 28-GHz applications

Abstract

A liquid-crystal (LC)-based floating electrode-free (FE-free) coplanar waveguide (CPW) phase shifter with an additional LC layer is demonstrated for the first time. An LC layer is overlain on the electrodes of the original model; this change increases the amount of electric flux that the proposed structure can confine in the tunable region, and thereby greatly increases the figure-of-merit (FoM) while maintaining the benefits of the simple coplanar structure. We simulated the variations in the phase shifter’s FoM, characteristic impedance, and driving voltage while sweeping the additional LC layer thickness up to 300 μm with each electrode condition at 28 GHz. In the case of electrode thickness variation, the FoM increased as electrode thickness increased, regardless of the presence of the additional LC layer. However, in the case of the signal electrode width variation, we obtained an opposite FoM tendency depending on the presence of the additional LC layer. This work shows the possibility of an efficient LC-based FE-free CPW phase shifter design for a given LC layer and electrode conditions.

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

“…Because fabrication technologies of the LCD industry are mature, so the price of LCD has been descending for decades. [6] If this decisive superiority could be exploited to produce an array of RF devices with many unit cells, we can achieve the advantage of cost-effectiveness compared to other solutions. The price of the phase shifters in a 4096-element (64 × 64) phased array antenna operating at 30 GHz could be only $100, assuming that the distance between adjacent elements is half the wavelength in air.…”

Evaluation of Surface-active Agent Hexadecyltrimethylammonium Bromide with Vertical Self-alignment Property to Align Liquid Crystals for Various Cell Gap Conditions

“…The grounded-CPW LCPS type has the same limitation because of the conductor-backed design. The floating-electrode-free CPW (FE-free CPW) can be implemented with the cell gap ≤ 20 µm, but to achieve sufficient tuning range, it requires the cell gap ≥ 100 µm [25]. These considerations illustrate that responses at large cell gap must be considered before the HTAB method is adapted for RF applications.…”

“…Although [HTAB] in 5CB was high enough, and a sufficient number of layers formed to the ITO glass surface, when the cell gap was too large, the fluidity and interaction forces among the molecules disturbed the homeotropic alignment, so it was not maintained throughout the LC medium. This limitation imposed by the cell gap means that that when HTAB is used as a surface-active agent for homeotropic alignment in RF structures, they must be designed to have the cell gap < 100 µm, perhaps by adjusting design parameters such as electrode conditions [25].…”

“…However, conventional LCD industry and smart-window applications that use LCs typically use a small cell gap (defined as the distance between two ITO-coated substrates), ≤ 10 µm and ≤ 20 µm, respectively [8,10,16,24], and the display industry has mature manufacturing capability for the cell gap. However, for RF applications, to maximize the tuning range of liquid crystal RF devices, a maximum thickness of 300 µm is needed [25].…”