Frequency Ripples Reduction in Differential Delay Time of Liquid Crystals Coaxial Delay Lines

As the millimeter-wave spectrum becomes increasingly pivotal for high-data-rate and beamforming applications, the development of tunable delay lines operating at 60 GHz has emerged as a critical area of research, wherein liquid crystals (LCs) are playing an enabling role for continuous tunability in the delay time. By characterizing the differential delay times of our LCs-enabled coaxially structured variable delay line design across the spectrum from 54 GHz to 66 GHz, undesirable ripples (standard deviation of 3.06 femtoseconds) are observed for this past design that was optimized for phase shift-to-insertion loss performance with impedance-matching at the LCs’ permittivity tuning status of 2.8. By suitably readapting the geometry’s impedance-matching baseline to the LCs’ permittivity state of 3.1, we achieve a nearly constant delay time with minimized amplitude variations (standard deviation reduced to 0.72468 femtoseconds) across 54 GHz to 66 GHz.