Retrodirective Phased Array Antenna for CubeSats

Abstract

This paper discusses the design of a retrodirective phased array antenna for CubeSat applications. A phased array antenna can offer high gain and beamforming capabilities to small satellites. Retrodirective capabilities allow the communication system to autonomously determine the direction of an incoming signal without prior knowledge, and form the beam appropriately to achieve maximum gain. The end result is a compact high gain antenna without strict pointing requirements or deployables. Simulation result demonstrate that retrodirectivity provides array gain improvement across the entire scan range of the array rather than just the steer angle. Further simulations show that the benefits of retrodirectivity are more significant in larger arrays. An architecture is proposed using existing COTS parts, with a power added efficiency of 37% for a 5 W power output. Analytic analysis shows that due to DC power overhead, EIRP drops in larger arrays; arrays larger than $3\times 3$ are impractical using the proposed architecture. A antenna design process is presented to meet the needs of the phased array, and a 2.2 GHz RHCP design with a 6 dBi gain and 2 dB axial ratio is shown. Test results highlight that errors in the phase shifters result in large errors in scanning accuracy. A method of calibration to correct for phase shift error is demonstrated.