Load pull

Load pull and Source pull are the processes of altering (pulling) the impedances at the output and input, respectively, of an RF device or component whilst measuring the device behaviour. This can be necessary when the device under test has a non-linear response. Harmonic load pull is load pull where the impedances at the harmonic frequencies are changed individually.

Load pull measurements are particularly useful for characterisation of amplifiers under large signal conditions, far from 50 Ω or the nominal line impedance.

Load pull: the process of varying the impedance seen by the output of an active device to other than 50 ohms in order to measure performance parameters, in the simplest case, gain. In the case of a power device, a load pull power bench is used to evaluate large signal parameters such as compression characteristics, saturated power, efficiency and linearity as the output load is varied across the Smith chart.

Harmonic load pull: the process of varying the impedance at the output of a device, with separate control of the impedances at F0, 2F0, 3F0, etc. A very tricky measurement!

-from www.microwaves101.com