The time-domain paradigm in microwave nonlinear simulation

Microwave and RF engineers have historically preferred a frequency-domain description of devices, components, circuits and systems, and almost always do so when linear operation can be assumed. Even when there are parts of a subsystem that unavoidably require a nonlinear description in terms of the time-domain, the strategy for simulation usually attempts to blend the frequency-domain and time-domain perspectives, such as in Harmonic Balance and its many variations. Nevertheless, because of its power and generality, there are situations when a purely time-domain approach may be preferable, recognising at the same time the challenges involved in converting what may be a naturally a frequency-domain representation of a circuit block into a convenient and useful form for time-domain usage. This paper will review the challenges involved and tackle some of the perhaps unwarranted and negative myths about adopting a time-domain approach in high frequency non-linear simulation. Examples will be provided to illustrate the potential of adopting a time-domain paradigm.