An Efficient and Linear SSPA With Embedded Power Flexibility for Ka-Band Downlink SatCom Applications

This article presents the design, realization, and experimental characterization of a solid-state power amplifier (SSPA) conceived for $Ka$ -band downlink (17.3–20.2 GHz) satellite communication (SatCom) applications. To the best of the author’s knowledge, this is the first space-borne SSPA realized for this peculiar application to achieve a technology readiness level of 5, entirely based on European technologies. All the activities carried out during the development phase will be discussed, starting from the power budget analysis, moving through the ad hoc design and characterization of the elementary 10-W microwave monolithic integrated circuits (MMICs) power amplifier (PA) in the 100-nm gate length gallium nitride (GaN) on silicon technology, and ending with the circuit solutions conceived to achieve state-of-the-art performance like saturated output power larger than 125 W with a gain and an overall efficiency better than 70 dB and 22%, respectively, while satisfying all the space-derating rules. The SSPA is composed of two subunits: the radio-frequency tray (RFT) to amplify the useful RF signal and the electronic power conditioner (EPC) to interface the module with the satellite primary bus, to actuate remote telecommand/telemetry services and to set different operating modes. The latter is based on a space-qualified microcontroller, whereas the former exploits a low-loss radial splitter/combiner structure in the waveguide to spatially combine the power provided by 16 elementary 10-W MMIC PA. The RFT also includes an input and output isolator, a gain control unit (GCU), a driver, and an analog linearizer. The latter helps to achieve a noise-to-power ratio (NPR) better than 18 dB when the SSPA is tested with a white-noise-like signal having a peak-to-average power ratio (PAPR) of 10 dB and an instantaneous bandwidth of 2.9 GHz. In this working condition, the SSPA provides an average output power and efficiency close to 100 W and 22%, respectively. Finally, it is worth mentioning that the SSPA is equipped with a power flexibility feature that allows it to reduce its power consumption up to 20%, depending on the actual RF power needed at the satellite level.