Abstract: A hybrid load pull tuner system uses a combination of a passive and active tuner system. A closed loop system means that the system is independent of the available power of the device under test (DUT). The proposed hybrid system is formed around a closed loop Gamma Boosting Unit (GBU) consisting of two back to back broadband directional couplers, broadband variable time-delay, broadband variable phase-shifter and a broadband microwave amplifier, all inserted in the coupled path of the couplers; the GBU is connected in cascade with a passive tuner and boosts its reflection factor; for this the amplifier must have enough linear power and gain to match the difference between the power reflected back to the DUT by the passive tuner and the desired total reflected power to reach the expected Gamma, considering coupling loss and insertion loss of the test fixture.