A Glance at Device Stability in Load-Pull Measurement Setups

Source-pull and load-pull techniques are widely used to characterize and test RF transistors. The measurement system varies source and load impedances to evaluate the performance of DUT. However, RF transistors are not unconditionally stable due to their physical structures. Therefore, they tend to oscillate during source-pull and load-pull measurements. A load-pull setup usually consists of couplers, tuners, bias-tees, circulators, and driver amplifiers. These components might cause resonances and trigger oscillations during measurements. In this study, the frequency response of a passive load-pull setup is analyzed in a wide range to understand the effect of measurement setup equipment on DUT's stability. The measured results show a considerable impedance variation outside of the operation band. Some solutions are recommended, and the necessity of new equipment is discussed.