Asymmetrical Doherty amplifier using GaN HEMTs for high-power applications

In this paper, we present an asymmetrical Doherty amplifier (DA) that can enhance the efficiency at a 9.5 dB backoff from its saturated output power (P
_SAT
). The asymmetrical DA consists of a peak amplifier and a carrier amplifier with two and one 210 W gallium nitride (GaN) high-electron-mobility transistors (HEMTs), respectively. A Wilkinson combiner at the output of the peak amplifier enables the stable operation of the GaN HEMTs for high-power applications. The asymmetrical DA is designed and fabricated for the ultrahigh-frequency (UHF) band. Measurement results using a continuous wave (CW) signal indicate a drain efficiency (η
_d
) of 60% at a P
_SAT
of 57.5 dBm and a η
_d
of 56% at a 9.5 dB backoff from P
_SAT
. For a 6 MHz orthogonal frequency-division multiplexing (OFDM) signal with a high peak-to-average power ratio (PAPR), the measurement results indicate a η
_d
of 52% and an adjacent-channel leakage power ratio (ACLR) of -41 dBc at an average output power (P
_AVE
) of 48 dBm using a digital predistorter. To the best of our knowledge, this is the highest η
_d
and output power for an OFDM signal.