Load Pull Characterization

Modern active devices in RF/microwave power amplifiers can deliver high output-power levels, at times over broad frequency ranges. But this requires establishing optimum source and load conditions for those active devices at as many operating frequencies as possible. Finding those optimum load conditions is possible by characterizing a device under test (DUT) while changing the impedance presented to the load at different frequencies while measuring to find the maximum output power at each frequency.

This can be done using Load Pull “LP” (or Source Pull, “SP”); this is a test method whereby a potentially nonlinear microwave device (typically a two-port, especially a microwave power transistor) is presented with varying loads while its RF and DC behavior is measured and registered. As in all experiment and measurement, only one external parameter (stimulus) is allowed to change, for being able to extract useful information. All other externally imposed parameters are test conditions and must remain controlled and constant.