Fast Optimization of RF Power Transistors with mmWave Active Load-Pull Techniques

The paper presents a peak-search method for active continuous wave (CW) load-pull measurements for implementation in an autonomous characterization system aimed at optimizing mmWave RF power transistors. The approach utilizes a downhill simplex algorithm to find a target impedance or to determine the optimal output impedances to achieve maximum output power or power added efficiency (PAE) in a load-pull system based on open-loop active injection. An 8-term error model with power calibration, based on large signal vector network analyzer (LSNA) equations is implemented, to ensure highly accurate measurements for the wave correction. The downhill simplex algorithm demonstrates excellent repeatability and robustness with a std of 0.08 dB in the output power over ten measurements and Γload std of 0.02 in magnitude and 1.78° in phase. It is shown to accurately identify the target load impedances while maintaining a fast convergence.