Design of a 120 W balanced GaN Doherty power amplifier

In this paper the design of a high power balanced Doherty power amplifier (PAs) will be reported. The Doherty PA was designed to achieve high average efficiency for digitally modulated signals with high peak to average power ratio (PAR) used in third (3G) and fourth (4G) generation systems. To achieve high efficiency up to 6 dB output power back-off (OPBO), a combined design technique of uneven power divider and use of unsymmetrical devices has been considered. At same time in order to improve its linearity and higher power capability a balanced structure, which combines two identical Doherty amplifiers has been proposed. For demonstration, a 120 W Doherty PA has been implemented to operate at 2.5 GHz. A drain efficiency of 57% (48% power added efficiency (PAE)) has been measured at its maximum output power of 50.8 dBm. Efficiency of more than 40% at the 6 dB output power back-off has been also measured. Moreover, the Doherty PA has been characterized using two-tone signal of 10 MHz spacing which resulted in a third order inter modulation ratio of -35 dBc at the 8.5 dB output power back-off level.