Liquid crystal based phase shifters in 60 GHz band

Preliminary structures and performance results of two different 60 GHz band planar phase shifters using liquid crystal (LC) are presented. The first phase shifter is based on a meandered microstrip line structure with the conductor pattern exposed to a layer of a nematic LC, while the second phase shifter is based on the reflection type microstrip line phase shifter structure whose tunable reflective loads are formed on a nematic LC substrate. The LC used in these two phase shifters is E7 with a low temperature coefficient over a wide range of temperatures. In both phase shifters, the LC is biased through a variable low voltage external source allowing for the control of the dielectric constant of the LC. To facilitate the on-wafer measurement and the application of the electric field to the LC, a broadband transition from the microstrip line to the CPW is developed and used in both phase shifters. The best figure of merit of the meandered line phase shifter, 20.8°/dB, occurs at 60.7 GHz coinciding with a differential phase shift of 243 degrees, while the RTPS achieves a maximum figure of merit, 12.3°/dB, at 61.31 GHz corresponding to a differential phase shift of 170 degrees.