A 220 GHz Reconfigurable Reflectarray Antenna Using GaN HEMT Device

Reconfigurable reflectarray antennas (RRAs) at sub-millimeter and terahertz frequencies are critical for communications and imaging applications. This study examines, fabricates, and measures an RRA integrated with a gallium nitride (GaN) high electron mobility transistor (HEMT) device, operating at 220GHz. A reflectarray element on a sapphire substrate, incorporating a GaN HEMT device and a matching circuit, is designed to achieve a 1-bit phase shift of the reflected wave. Detailed analyses of the HEMT device model and the sub-millimeter element design are conducted. The proposed RRA is fabricated using standard chip processes, resulting in a 16×16 element array on an 11.2×11.2×0.1mm³ chip. The 1-bit phase-shift performance is validated through two-state reflection coefficient measurements. Due to the fabrication challenges of element control, a column-control biasing network is implemented. The 1-D beam-scanning capability of the RRA prototype is experimentally demonstrated at 220GHz, achieving a scanning angle of up to 40°. The experimental results demonstrate strong agreement with theoretical predictions.