Design and characterisation of an outphasing power amplifier with balun combiner

This paper presents an outphasing power amplifier using a planar balun as power combiner. The balun with bandwidth extending to and over octave was fabricated using thin film technology on alumina substrate. The design adopts a hybrid approach, utilising a pair of bare die devices with bond-wire connections to the alumina passive networks, to minimise the extra parasitic effects introduced by packaging. The characterised prototype, that uses the TGF2023-01-2 12 W GaN HEMT from Qorvo, operates at centre frequency of 1.9 GHz and demonstrates a 15% bandwidth, where the maximum output power is maintained within 0.5 dB deviation from 41.2 dBm. On the same bandwidth, the PAE is above 55% and 44% when operating at its peak and 6 dB output back-off (OBO) output power, respectively. The Power back-off is realised by both amplitude and relative phase modulation.