Signal-Flow-Graph Analysis of Weakly Nonlinear Microwave Circuits Around a Large-Signal Operating Point

A signal flow graph (SFG) representation of small-signal responses nonlinear microwave circuits around a large-signal operating point is developed using the X-parameters. It shown that, unlike SFGs for linear circuits, negative-frequency nodes need to be included explicitly. The development elucidates circuit-operational meaning elusive T-type X-parameters, which represent interaction between positive-and components. As an example, such SFG used derive closed-form expression output power amplifier as function load reflection coefficient. then plot approximate load-pull contours. result consistent with expressions optimum coefficient derived by Root et al. (EuMIC 2017) and contours Peláez-Pérez (TMTT 2013). provide alternative systematic means in terms X-parameters gain illuminating insights into workings weakly circuits.