A wideband GaN Doherty amplifier with 35 % fractional bandwidth

A wideband Doherty amplifier designed and implemented in GaN HEMT technology using simple circuitry is reported. The usefulness of the conventional quarter-wave impedance transformer at the output of the main amplifier for achieving wideband Doherty performance up to 35 % fractional bandwidth is experimentally verified. This simplifies the bandwidth limitation problem of the Doherty amplifier into the wideband design of the main amplifier, peaking amplifier and the input power divider. Based on this, a wideband Doherty amplifier was designed to cover a bandwidth of 640 MHz, ranging from 1.5 GHz to 2.14 GHz. For instance, the designed Doherty amplifier achieved a 1 dB compression output power of P1dB = 43.8 dBm (24.1 W), with a maximum power-added efficiency of PAE = 69 % (drain efficiency of η = 76 %) at 1.9 GHz. At 6 dB output back-off from P1dB, a PAE of 45 % (η = 47 %) was measured. The designed Doherty amplifier also showed acceptable linearity when characterized with two-tone and single-carrier wideband code-division multiple access (W-CDMA) stimuli. To the best of authors' knowledge, this work introduces the most wideband Doherty amplifier published so far.