Microwave High-Speed Liquid Crystal Devices Using CPW with Floating Electrode

Abstract

We develop a transmission line with a floating electrode (FE) arranged on a coplanar waveguide (CPW), and we propose using this transmission line to reduce the decay time of a microwave-band liquid crystal loaded device. Using the proposed CPW-FE structure makes it possible to control both the rise time and decay time by varying the applied bias field, thereby allowing the decay time to be reduced. In the 18 GHz band variable phase shifter we developed, we obtained a rise time of 75 ms and a decay time of 200 ms with a 500 μm wide CPW center conductor, a gap of 20 μm between the center conductor and ground plane, and a liquid crystal layer thickness of 50 μm. Under these conditions, the birefringence Δϵ′ of the liquid crystal was 0.23.