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In this paper, the Doherty like load modulation has been implemented in second-harmonic-tuned gallium nitride (GaN) power amplifiers (PAs) to further improve their performance. Both harmonic tuning and load modulation are based on an accurate large-signal model extracted for the GaN devices. Two devices of identical size are used. In previous research works, the use of load modulation on two identical size devices always results in decreases in output power, gain, or even linearity, although improvements in efficiency are shown. Besides that, the influence of the offset line on linearity is not covered. In this experiment, by optimizing the load modulation and properly designing the offset line, a power added efficiency (PAE) of 65%, a linear gain of 16 dB, and an output power of 40.5 dBm have been achieved at 2 GHz. Compared with those of a balanced power amplifier, the load modulated PA shows superior power performance both in efficiency (more than 10% improvement in PAE) and in linearity. Moreover, its output power and gain maintain as high as that of the balanced PA.
Date of Conference: 12-15 Oct. 2008