The Role of Nonlinear Microwave CAD in RF Power Amplifier and Active Antennas Design

RF power amplifier design constituted one of the major driving forces for the development of nonlinear microwave circuit simulation tools, and, today, it still heavily relies on it. When nonlinear circuit simulation is invoked, the name of Prof. Vittorio Rizzoli, one of its key contributors, immediately comes to mind. Hence this work is aimed at describing how nonlinear microwave CAD became a game changer in the design of RF PAs, going all the way from the basic efficiency and output power prediction under CW excitation, passing through Rizzoli´s multidimensional Fourier transform-based multi-tone distortion analysis, to the envelope-driven harmonic-balance simulation of RF PAs subject to real modulated signals. Finally, a new CAD strategy, developed for combining nonlinear analysis with electromagnetic simulation, is discussed as a fundamental add-on to specify nonlinear (circuital) and radiative figures of merit simultaneously, which is a breakthrough for this class of RF systems.