A millimeter-wave quasi-optical grid phase shifter using liquid crystal

A new type of millimeter-wave quasi-optical variable phase shifter which exploits the dielectric anisotropy of liquid crystal (LC) materials is presented. The device is operated in transmission mode and consists of inductive and capacitive metal grids, each patterned on a dielectric substrate, which are separated by a thin layer of LC. The grids together with the LC form a parallel resonant circuit. Prototype devices with a 25-μm-thick LC layer for use at a millimeter-wave frequency of 50GHz were designed and fabricated. Experiments performed at U-band frequencies show that a phase shift of 7.8° is obtained with a low insertion loss of ~ 0.6dB at the resonant frequency by applying a control signal of 20V. Good time response for the device is demonstrated. It is suggested that the phase shift attainable with the device can be further enhanced by using LC materials with larger dielectric anisotropy and/or thinner dielectric substrates.