This letter presents an automatic power amplifier (PA) design methodology that uses a multi-dimensional search algorithm to find the best compromise between fundamental and harmonic impedance terminations for a specified bandwidth. In conventional design methodologies, PA designers need to pre-select the optimum impedances, which normally follow non-Foster trajectories, and are thus impossible to achieve with passive matching networks for a wide frequency range. Instead, the proposed automatic design method directly synthesizes the matching networks to achieve the desired output power, efficiency, and gain performance, without forcing any impedance profiles. For that, load-pull data is interpolated using artificial neural networks, and an algorithm based on the simplified real frequency technique is used to obtain the matching networks. Finally, the method is validated with a single-ended PA implementation.