Compact and Broadband Millimeter-Wave Electrically Tunable Phase Shifter Combining Slow-Wave Effect With Liquid Crystal Technology

Based on a CMOS slow-wave coplanar-waveguide transmission-line topology, a novel compact millimeter-wave phase shifter is presented. The tunability is accomplished by using a liquid crystal (LC) material as a tunable dielectric between the coplanar signal strip and the shielding plane of the slow-wave transmission line. The device tunability is considerably enhanced by moving the free-standing signal strip with the application of a bias voltage. Combining the miniaturizing benefits of the slow-wave effect with the continuous tuning of LC material, the proposed device occupies only 0.38 mm² and exhibits high performance. The phase shifter was characterized up to 45 GHz for a maximum bias voltage of 20 V without significant power consumption. The reproducible measurements show a figure-of-merit (ratio between the maximum phase shift and the maximum insertion loss) of 51°/dB at 45 GHz.