Traditional load pull was the first system to automatically measure device performances under various source and load impedances. These test benches are using pre-characterized passive tuners for impedance matching and scalar power detectors for measurements.
Based on the pre-characterization of the impedance tuners, the measurements are relying on the set of measured or interpolated s-parameters of the tuners at different impedance conditions. Raw measurements from scalar instruments (Power meters) are de-embedded, in real time, to the DUT reference plane using the loss calculation of tuners and other components in the setup.
The accuracy of the measurements relies entirely on the quality of the calibration and the mechanical repeatability of the tuners. This load pull architecture is cost-effective.