Abstract: The present Chapter is concerned with modelling of excitation in real life microwave ovens. This is in extension to Chapter 18, where the computational model is truncated within the waveguide connecting the oven to the source, and the actual source is represented by the fundamental waveguide mode, assumed to have a well-defined frequency (or frequency range) and amplitude. In the first major part of this Chapter we summarise the uncertainties associated with the frequency spectrum of signals generated by magnetrons in domestic ovens. We further show how those uncertainties can be taken into account in deterministic modelling of the oven scenarios. Specifically, we propose an efficient time-domain approach, which allows one to generate load heating patterns and to calculate the overall oven efficiency in a single simulation performed in response to a Gaussian pulse whose spectrum mimics that of the magnetron. In the final part, we refer to new oven design perspectives associated with solid state sources and discuss several modelling regimes that make such design work easier and faster.