3.5 GHz WiMAX GaN doherty power amplifier with second harmonic tuning

The article presents the design, realization, and experimental validation of a GaN-based hybrid Doherty power amplifier for WiMAX base-stations at 3.5 GHz. The amplifier exploits, for the first time as far as authors' knowledge goes, a second harmonic tuning scheme designed to further improve the efficiency in the Doherty region. The amplifier is based on a packaged GaN HEMT from Cree, and shows a saturated output power exceeding 43.2 dBm (21.5 W), a Doherty high-efficiency region in excess of 6 dB output back-off, with a first peak and maximum drain efficiency at saturation of 55 and 61%, respectively. The amplifier, with baseband digital predistortion, is compliant with the standard emission mask in the presence of a 9 dB peak to average power ratio WiMAX input and exhibits a weighted efficiency as high as 40%. The performances of the designed amplifier favorably compare with the state of the art for the same application.

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