Ferroelectric- and liquid crystal- tunable microwave phase shifters

This paper introduces two different low-cost, voltage-controlled tunable phase shifter devices based on (1) coplanar waveguide on a ferroelectric thick film ceramics and Al₂O₃-microwave substrate and (2) inverted-microstrip line with standard and novel liquid crystal (LC) in-between. For the first type, the differential phase shift can be controlled continuously and exceeds 360° at 38 GHz for a maximum dc voltage of 100 V, corresponding to an electrical field strength of 3.3 V/μm. The best phase shifter figure-of-merit values, i.e. the quotient of differential phase shift and insertion loss, amounts to 15 to 28°/dB at 24 GHz for a maximum field strength of 10 V/μm. This can be increased up to 50°/dB at 24 GHz for very high field strengths above 20 V/μm. In contrast, with comparatively low control voltage of 40 V (0.18 V/μm), the figure-of-merit of the LC type phase shifter amounts to 16°/dB at 20 GHz for a standard nematic LC K15 and 68°/dB for an advanced LC mixture.