Continuous tunable miniaturized microwave coupler using liquid crystals

This paper describes a microwave coupler using liquid crystals as a medium for microstrip line structure. In this design, a layer of liquid crystals is added to the ground and the substrate, and using the characteristics of anisotropy nematic liquid crystals, that is the dielectric anisotropy changes when without the bias and bias voltage is applied, to achieve the goal of continuous tunable coupler center frequency. In this paper, the design of the coupler not only has a wide bandwidth, but also the isolation (|S41|) and return loss(|S11|) are relatively excellent, especially in the center frequency, which are all better than 45dB. When the permittivity of the liquid crystals is changed from 2.4 to 3.4, the center frequency of the coupler is changed from 2.85GHz to 2.75GHz; the tunable range of up to 100MHz has been realized.