Reconfigurable Unit Cell Design Using MEMS Actuator for Beam-Steering Applications

This article proposes a reconfigurable reflective unit cell utilizing micro electro-mechanical system (MEMS) actuator at Ku-band for use in reconfigurable reflective arrays. The proposed unit cell consists of a MEMS actuator and an electric-LC (ELC) resonator with its capacitive slot extended to two pads in the ground plane using two vias. The MEMS actuator is positioned beneath the ground plane spaced with a gap from the two pads. The total capacitance of the unit cell will change by the actuator’s movement, resulting in a variation in reflection phase. The utilized MEMS actuator is a thermal actuator with large displacement of about 1 mm. It was fabricated using PolyMUMPs process which is a three-layer polysilicon micromachining process. To validate the simulation results, a prototype of the proposed unit cell was fabricated and measured using a waveguide measurement set up. Measurements are in good agreement with simulation results, showing a continuous 260° reflection phase at 13.2 GHz. Additionally, an $11\times 11$ elements reflect array was simulated in different modes to shows versatile beam-steering capability of the proposed structure. Simulation results show satisfactory beam-steering capability using proposed structure in the array. Although the proposed structure was employed at Ku-band, the underlying concept promises to be highly useful in beam-steering application at millimeter-wave and sub-terahertz frequency bands, where semiconductor technology fails to provide tuning elements with a reasonable RF performance.