DUT input impedance measurement in an automated load-pull system

Using a Load pull system to find the input matching needed for a device has become a standard practice in the industry. However, this information can be misleading if care is not taken to reduce the measurement uncertainties. The largest contributor to the uncertainties of the return loss measurement comes from the directional coupler, its directivity and the losses between the coupler and the DUT. These uncertainties are systematic and therefore can be mathematically calibrated out. One of the limitations is the lack of phase information needed measure the impedance of the DUT. With the correction method being used the phase information is now available and the DUT impedance can now be measured. I will show some of the theory behind correction techniques, the measurement used and the test results.