Frequency-Domain Analysis of Electrically and Thermally Nonlinear Microwave Circuits

The simulation of temperature-dependent microwave circuits under large-signal multitone excitation is reduced to the simultaneous solution of two coupled nonlinear circuits. One of these represents the conventional electric circuit, while the other is the equivalent circuit of the heat flow from the active devices. Under steady-state conditions the two networks are analysed by a novel implementation of the piecewise harmonic-balance technique. This provides a robust and efficient analysis tool for microwave power circuits operating in pulsed-RF conditions, including the effects of the thermal resistance nonlinearity and of a non-ideal multilayer heat sink. The thermal circuit parameters are found directly from geometrical information.