Active load pull tuning is, because of limited tuning range of passive tuners, additionally reduced by fixture and probe insertion loss, the only method allowing test engineers to reach up to |Γload|=1 (RDUT=0Ω) to match any DUT at its reference plane. In closed loop active tuning, part of the extracted RF power from the DUT is amplified and fed back into the DUT output port, creating a virtual load. Since the re-injected power can be higher than the original extracted power, Γ can be >1, meaning that insertion loss can be compensated. Using two (or more) synchronized (coherent) sources allows open-loop active (and harmonic) tuning; in fact the loop here is also closed, but, instead at RF, it is closed at IF synchronizing reference.
Focus offers also active source pulling technology, based on the Gamma Boosting Unit (GBU) and several associated techniques. Active load pull requires high power feedback amplifiers. Combining with pre-matching passive wideband (CCMT) or harmonic (MPT) tuners, in a Hybrid configuration, allows reducing the PA requirements by a factor of 10. The RAPID electronic active tuner technology, developed by MESURO, allows high speed load pull (50 points/second), 100 MHz modulated signal as well as hybrid and harmonic tuning.