Development of a space-grade Ka-band MMIC power amplifier in GaN/Si technology for SAR applications

This article presents the complete characterization of a Ka-band monolithic (MMIC) high-power amplifier (HPA) developed with a commercial 100-nm gallium nitride (GaN)/Si process provided by OMMIC (now MACOM). The amplifier was conceived for a space-compliant environment, focusing, in particular, on pulsed radar applications, e.g., for synthetic aperture radar (SAR) altimetry. The amplifier is designed accounting for the critical reliability constraints posed by the space environment. Due to the poorer thermal characteristics of GaN/Si technologies compared with their GaN/SiC counterparts, proper thermal-aware criteria are needed to be exploited during the design process. The fabricated MMIC has been characterized under different biasing and temperature conditions and finally tested with a representative SAR signal. The amplifier achieves at 36 GHz an output power of 10, 8.4, and 6.6 W when biased with a drain voltage of 11.25, 10, and 9 V, respectively, with an associated PAE around 20% and a linear gain of roughly 20 dB under all biasing conditions and with an MMIC backside temperature ranging from - 10C up to + 80 C. With a 9-V bias, the designed MMIC is fully compliant with the maximum derated junction temperature limit of 160C recommended for space reliability in both pulsed and continuous-wave (CW) operations, demonstrating performance well in line with the state of the art for this technology when a space-grade design is required.