Large-signal stability analysis of microwave amplifiers under complex modulated signals with time-varying envelope

A methodology is proposed to analyze and predict the variation of the stability margins of microwave amplifiers when time-varying envelope signals are considered. The methodology starts from well-established harmonic-balance techniques for the detection of parametric oscillations under continuous-wave excitation. These techniques are then completed with an envelope-transient analysis, requiring appropriate initialization of the autonomously-generated frequencies. The methodology is developed on a 4GHz amplifier specifically designed and built as a test bench for parametric oscillation analysis. Bifurcation diagrams for two-tone and filtered x/4-DQPSK signals evidence the shift of the stability margins due to the time-varying envelopes.