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What is active and hybrid load pull?

An active load pull system provides the same functionality of a passive system, but is not comprised of the traditional passive electromechanical tuners found in most systems. A purely active system is simply an active loop which modifies the output signal of the device and re-injects it back to the device at a given phase and amplitude. If the active loop has enough power the system will allow coverage of the entire smith chart, something a passive system cannot do. Below are two examples of simple architectures of two different active injection loops.

Closed-Active-loop-of-load-pull             Open-Active-loop-of-load-pull
Closed Active Loop   Open Active Loop

Key advantages of an active load pull system

  • The tuning range is not limited by the loss of the RF path between the tuner and the DUT
  • Tuning speeds are in the millisecond range as there are no mechanical parts to move
  • The large signal input impedance can be measured


  • Cost of linear amplifier required to compensate for load mismatch
  • Not applicable for input device tuning
  • Stability issues

Hybrid Load Pull

As per its name a hybrid load pull system includes both an active loop as well as the passive tuners. Below are two diagrams of fundamental and harmonics systems. The hybrid system has all the advantages of speed and tuning range of an active system as well as the power handling of a passive system.

Hybrid Active Load Pull Diagram       Harmonic Hybrid Active Load Pull Diagram
Fundamental Hybrid Active Load Pull Diagram   Harmonic Hybrid Active Load Pull Diagram


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