ABSTRACT
This chapter discusses the operation, setup, and verification of load-pull systems used for characterization of high-power transistors used in wireless applications. In both portable and infrastructure wireless systems the power amplifier often represents the largest single source of power consumption in the radio. Significant effort is devoted toward developing high-performance radio frequency and microwave transistors and circuits to improve power amplifier efficiency. The load signal is sampled at a directional coupler after the high-power pad. Due to the extremely low impedances synthesized in high-power load-pull, the vector network analyser calibration is the single most important element of the characterization process. Load-pull as a design tool is based on measuring the performance of a transistor at various source and/or load impedances and fitting contours, in the gamma-domain, to the resultant data; measurements at various bias and frequency conditions may also be done.
