Passive tunable liquid crystal finline phase shifter for millimeter waves

In this paper, the investigation of a finline based phase shifter device filled with liquid crystal, fed by a standard rectangular Ka-band waveguide, is described. A broadband transition from waveguide to antipodal finline is investigated and optimized, leading to an insertion loss of below 1.7 dB of the back-to-back transition. An antipodal finline transmission line filled with liquid crystal between its overlapping conductors is used as a phase shifter. Two different liquid crystals are investigated: K15 as a quasi-standard and MDA-03-2838 as a novel mixture with a steeply increased dielectric anisotropy and reduced losses compared to K15. At 40 GHz, a phase shift of 75° arises in connection with 8dB insertion loss for K15 whereas the phase shift of MDA-03-2838 amounts to 303° and 4.8 dB insertion loss, all measured at room temperature. Additionally, the response times of the phase shifter device are investigated for both liquid crystals.