Liquid crystal based phase shifter in a parallel-plate dielectric waveguide topology at V-band

This work presents a simple approach for a continuously tunable phase shifter design based on liquid crystal (LC) technology for the V-band. The main component of the phase shifter is a partially dielectric filled parallel-plate waveguide. For continuous tunability, liquid crystal is inserted inside the dielectric slab. This assembly, being fed by WR15 waveguides, maintains a simple and efficient way to realize the necessary electric biasing in comparison to hollow waveguide based LC phase shifter. A novel stepped impedance design, which is fabricated on an Ultralam 3850HT substrate is presented. The electrode design is based on Babinet's principle to obtain a homogeneous distribution of the biasing field. Using a voltage of ±150 V, a maximum differential phase shift of 380°, accompanied with an insertion loss between 2.4 to 3.6 dB could be achieved, yielding a high figure of merit of around 113 °/dB at 68 GHz.