7 GHz GaN MMIC power amplifier for Microwave Radio links with 45% drain efficiency in a wide power range

An MMIC GaN Doherty power amplifier is presented. This amplifier, optimized for C-band Microwave Radio links, is designed to reach the maximum efficiency at the output power back-off level where the data distribution function of the modulated input signal has its maximum. The design approach was carried out through a careful investigation of load pull measurements at the fundamental and second harmonic, in conjunction with an accurate active device model, thus leading to a robust design strategy. The designed PA shows, at 7 GHz, a maximum PAE of 35% at more than 7 dB of back-off from the maximum output power and the Doherty high efficiency region covers a 10 dB back-off range from saturation; the maximum output power is in excess of 37 dBm. The MMIC power amplifier has been fabricated at the GigaHertz Centre of Chalmers University, within a collaboration Politecnico di Torino-Ericsson Telecomunicazioni S.P.A.