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 (112, 114) 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 (112, 114) 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.