A calibration unit that separately calibrates real and imaginary parts of a load impedance of a power amplifier , the calibration unit comprising: an adaptive impedance unit operatively connected to an output of the power amplifier , said adaptive impedance unit comprising first and second variable impedance elements configured to independently tune the imaginary and real parts of the load impedance, respectively; a peak voltage detector , operatively connected between the output of the power amplifier and a controller , to measure a plurality of peak voltages produced at the output of the power amplifier ; and the controller operatively connected to the adaptive impedance unit and configured to respectively calibrate the imaginary and real parts of the load impedance by: selecting a first calibration value for the first variable impedance element from a first plurality of impedance values, said first calibration value producing a first calibrated voltage (V out ) at the output of the power amplifier greater than voltages produced at the output of the power amplifier by the remaining first plurality of impedance values; and selecting a second calibration value for the second variable impedance element from a second plurality of impedance values, said second calibration value producing a second calibrated voltage (V out ) at the output of the power amplifier that meets or exceeds a reference voltage. an adaptive impedance unit operatively connected to an output of the power amplifier , said adaptive impedance unit comprising first and second variable impedance elements configured to independently tune the imaginary and real parts of the load impedance, respectively; a peak voltage detector , operatively connected between the output of the power amplifier and a controller , to measure a plurality of peak voltages produced at the output of the power amplifier ; and the controller operatively connected to the adaptive impedance unit and configured to respectively calibrate the imaginary and real parts of the load impedance by: selecting a first calibration value for the first variable impedance element from a first plurality of impedance values, said first calibration value producing a first calibrated voltage (V out ) at the output of the power amplifier greater than voltages produced at the output of the power amplifier by the remaining first plurality of impedance values; and selecting a second calibration value for the second variable impedance element from a second plurality of impedance values, said second calibration value producing a second calibrated voltage (V out ) at the output of the power amplifier that meets or exceeds a reference voltage. selecting a first calibration value for the first variable impedance element from a first plurality of impedance values, said first calibration value producing a first calibrated voltage (V out ) at the output of the power amplifier greater than voltages produced at the output of the power amplifier by the remaining first plurality of impedance values; and selecting a second calibration value for the second variable impedance element from a second plurality of impedance values, said second calibration value producing a second calibrated voltage (V out ) at the output of the power amplifier that meets or exceeds a reference voltage. <EOS>