Design and baseband predistortion of a 43.5 dBm GaN Doherty amplifier for 3.5 GHz WiMAX applications

This paper presents the design concept and experimental evaluation of a Doherty Power Amplifier for WiMAX applications at 3.5 GHz. The amplifier, exploiting a packaged GaN HEMT from Cree Inc., shows a saturated output power exceeding 43.5 dBm (22 W), a Doherty high efficiency region of 7 dB, with a first peak efficiency of 57% and maximum drain efficiency of 65 % at the amplifier saturation. The amplifier has been characterized first at RF in continuous wave, and then with a WiMAX modulated input signal with 7dB PAPR, therefore allowing for a digital predistortion scheme to be extracted. The linearized amplifier shows more than 10dB ACPR reduction with respect to the unpredistorted case, while maintaining the same output power of 37.2 dBm (5W), and the same average efficiency of 51%.