Loss Analysis for Compact Liquid Crystal Delay Lines Based on Defective Ground Structures

This paper analyzes loss contributions in novel, high-performance Liquid Crystal (LC) microstrip delay lines with defected ground structures. While providing a significant miniaturization of the tunable delay line, the aforementioned topology enables low losses despite thin LC layer thickness, which is a requirement for millisecond LC response times. These features result in a wide range of potential applications, including but not limited to phased arrays, reflectarrays and reconfigurable intelligent surfaces. Within this contribution, we conduct a comprehensive comparative analysis with a focus on dielectric and conductor loss contributions between a conventional inverted microstrip line (IMSL) and the defected ground structure IMSL (DGS-IMSL). The DGS-IMSL achieves a high FoM above 70°/dB in a bandwidth of 8.8 GHz (30%) at 28.8 GHz in measurements, despite a thin LC layer of only 4.6 μm.