Linearisation of Satcom Power Amplifiers

Abstract

The ultimate objective of this work was to develop a demonstrator of a highly efficient, GaN based, linearised, passively cooled solid-state power amplifier (SSPA)for avionic SATCOM terminals operating in L-band. The SSPA should provide sufficient output power to comply with all SATCOM classes in all installation options, meet all in-band and out-of-band distortion limits such as error vector magnitude (EVM)and spectral regrowth, and guarantee reliable operation for 1M-hours. The contract, undertaken with European Space Agency (ESA)funding, mandates the use of Gallium Nitride (GaN)technology and power amplifier linearisation techniques to maintain high efficiency, while operating in a linear fashion. The SSPA needs to meet all requirements without any forced-air cooling. The project has been completed successfully, achieving the 47% PAE target, while amplifying a single-carrier test waveform (Inmarsat R20T4.5X type waveform with 16-QAM modulation and 151.2kS/s symbol rate)to ~ 15W nominal / ~ 65W peak power level. Digital predistortion (DPD)linearisation was used to achieve <; 2% EVM and > 10dB margin in spectral regrowth measured against the ETSI (European Telecommunication Standards Institute)and Inmarsat channel masks at all offset frequencies. Passive cooling was demonstrated with GaN junction temperature not exceeding 150°C (absolute maximum rating 275°C)and mean-time-to-failure (MTTF)reliability of more than 10M hours.