Design and Realization of Doherty Power Amplifier Based on Active Load- Pull Measurements

Energy-efficient power amplifiers capable of supporting advanced communication standards are essential for the expanding wireless infrastructure. The Doherty power amplifier (DPA) is one of the most common high efficiency power amplifier (PA) architectures. However, the DPA is significantly sensitive to model accuracy due to its complex design, leading to sub-optimal performance. A proposed solution to overcome this barrier of inaccuracy is to use measurement data from an experimental active load-pull setup. In this work, an active load-pull system was developed, tested and used in the characterization of a 10W GaN HEMT. The characterization data were used in combination with a new DPA design approach, intended to provide an improved efficiency and linearity tradeoff, to design and fabricate a DPA. The developed active load-pull system was used for fast acquisition of load-pull data in a wide range of input and output power levels. The system was developed using modular components, allowing an easy adjustment to the specific needs of any future project. The characterization of the GaN device was conducted by using a precursor development board (DB). The DB contained the device along with its stability network and second harmonic and baseband terminations. The DB was characterized at different power levels of interest and was used as is in the final DPA design. The designed and fabricated DPA presented excellent performance with good agreement with the theoretical predictions, verifying the robustness of the implemented designed method. The DPA was designed to operate at 2.14 GHz and reached an output power level of 40.8 dBm which was 1.5 dB less than the expected, and with a gain of 11.4 dB at back-off (BO) and 10.9 dB at full power (FP). The power added efficiency at -6.2 dB BO was 42.3 % and 50.1 % at FP. The phase response of the DPA presented a distortion of 8.8 degrees at BO and 17.6 degrees at FP. The developed active load-pull system proved to be a powerful tool for characterizing transistors for PA design. However, the final results indicate that the system needs further improvements in the accuracy of the measurements. That being said, this thesis is as an important milestone for the quest of making better PAs required for future wireless communication systems