System level characterization and digital predistortion of GaN MMIC Doherty power amplifiers for microwave point-to-point radios

In this paper, the system level characterization and linearization of two GaN monolithic Doherty power amplifiers for 7 GHz backhaul transmitters is presented. In particular, the two different design techniques, aimed to reduce the gain penalty tipically affecting the Doherty topology, are briefly introduced. Both amplifiers can deliver more than 5W of output power, with good back-off efficiency. An advanced system level characterization setup, enabling accurate on-wafer measurements, is deployed to characterize and linearize the power amplifiers. In particular, system level performance after predistortion, compliant with regulamentation constraints, are reported, highlitghing the benefits and drawbacks of the two different design strategies.