Bias Smith Tube Optimization of Drain Voltage and Load Reflection Coefficient to Maximize Power-Added Efficiency Under ACPR Constraints for Radar Power Amplifiers

Reconfigurable transmitter power amplifiers will be necessary in future cognitive radar systems to allow adjustment in operating frequency, spectral output, and other desired operating characteristics while maintaining performance. Circuit optimization algorithms for tuning the amplifier load impedance and bias voltage in real time should maximize power-added efficiency while limiting the adjacent-channel power ratio (ACPR) in order to obtain spectral compliance. This paper presents a fast vector-based three-dimensional optimization for simultaneous bias adjustment and impedance matching for these goals using the bias Smith tube as the optimization space. Simulation and measurement results are presented for this optimization algorithm, and correspondence between the results is examined for several different starting locations in the bias Smith tube. This algorithm will allow simultaneous optimization of bias voltage and load impedance in real time in order to meet changing requirements.