Active harmonic load-pull system for characterizing highly mismatched high power transistors

High-power devices (>30W) require low load impedances (<5Ω) for optimum power performance. In presenting the necessary fundamental and harmonic impedances, traditional passive load-pull systems are restricted by inherent system losses. Active load-pull can compensate for this problem, but unfortunately does not scale well with high power applications. This paper presents a novel solution allowing harmonic load-pull characterization of high-power devices. Broadband impedance transformers allow the necessary load-pull power to be dramatically reduced whilst maintaining the accuracy and integrity of measured waveforms. This approach has been successfully demonstrated through the measurement of a 30W LDMOS device, where the required active load-pull power required to present the optimum load has been reduced from 270W to 50W.