Design Margin of Millimeter-wave Ultra-wideband 0-180° Analog Delay Line with Insertion Loss Less Than 2 dB

Achieving a liquid crystal-based millimeter-wave low-loss (e.g., less than 2 dB) 0-180° continuously variable delay line at 60 GHz band is a highly valuable but technically demanding task. This study deals with the design margin investigation based on experimental and computational analyses of an inverted microstrip (IMS) passive delay line enabled by nematic liquid crystals (NLC) as highly variable dielectrics covering 1-67 GHz operation. The IMS true-time-delaying device is constructed with a 125 μm-thick NLC layer (GT3-24002) that encloses in part of a copper core line measuring 220 μm-wide, 17 μm-thick, and 1.35 cm-long. Free from metal surface roughness and other manufacturing tolerance-induced losses, the device achieves a differential phase variation of 0-180° with a maximum insertion loss checked against a threshold of 2 dB for various industrial applications. At 30 GHz, it is possible to allocate a margin of 1.14 dB for unaccounted losses, whereas at 60 GHz, this margin decreases to 0.4 dB, posing a greater challenge in achieving the objective. The quantification of the performance metrics offers significant insights into the optimization of IMS delay lines that utilize NLC as a tunable dielectric medium for applications that are critical to mission success.