High efficiency 25 Watt GaN X-band SSPA for deep space missions

Abstract

Deep space missions often require a rugged, high efficiency, low mass X-Band power amplifier to return science data back to Earth. A high efficiency 25 W GaN solid state power amplifier (SSPA) prototype was developed for NASA's Europa Lander mission concept. The SSPA design consists of three amplifier stages each designed using a die-level GaN on SiC high electron mobility transistor (HEMT). The first two stages are single string amplifiers and the final output stage consists of two stages in a quadrature combined configuration, to provide both soft-redundancy and improved heat spreading, which increases reliability. The design also uses a low-loss isolator on the output to ensure that any changes in the SSPA's load impedance (i.e: the antenna) is minimized, thereby reducing any degradations to the two main requirements of the SSPA, output power and efficiency. Also, an efficient DC-DC converter that converts the Spacecraft Bus voltage (22 V to 36 V) to a regulated 32 V is designed. Each function block in the SSPA is measured individually and the overall cascaded performance is calculated based on these measurements. The final performance of the SSPA results in an output power 25 W, at a box efficiency of 37.5%. This is an improvement from traditional GaAs SSPAs that have previously flown and an improvement from recent published GaN SSPA results. [1]