Fast, simultaneous optimization of power amplifier input power and load impedance for power-added efficiency and adjacent-channel power ratio using the power smith tube

Reconfigurable adaptive amplifiers are expected to be a critical component of future adaptive and cognitive radar transmitters. This paper details an algorithm to simultaneously optimize input power and load reflection coefficient of a power amplifier device to obtain the largest power-added efficiency (PAE) possible under a predefined constraint on adjacent-channel power ratio (ACPR). The vector-based search relies on estimation of the PAE and ACPR gradients in the three-dimensional power Smith tube. Accurate convergence to the optimum impedance in the Smith chart is demonstrated in simulation and measurement search experiments requiring between 20 and 60 experimental queries. This paper presents a fast search to jointly optimize the input power level and load impedance. This method is feasible for future implementation in real-time reconfigurable power amplifiers.