Adaptive load impedance optimization for power amplifiers in reconfigurable radar transmitters.

A fundamental tradeoff exists in radar transmitter design between linearity and efficiency due to the signal amplification. These transmitters are driven into saturation in order to increase efficiency, but may potentially violate regulatory spectral mask limitations. An adaptive method for optimizing linearity and efficiency for power amplifiers in radar transmitters is presented. This approach uses intelligent search techniques with load-pull measurements for power-added efficiency (PAE) and adjacent channel power ratio (ACPR) to dynamically maximize the PAE while meeting spectral requirements. Using load-tuning, an algorithm performs a steepest ascent search for the PAE optimum load reflection coefficient, followed by a steepest descent search for ACPR. The steepest descent search, when begun at the PAE optimum, approximates the Pareto optimal frontier between the two objectives. This trace enables PAE to be maximized for an imposed limit on ACPR, optimizing the performance of adaptive radar transmitters under spectral mask constraints.