The fundamental importance of dynamic modeling of electromagnetic fields in space and time

Frequency domain or time-harmonic models are ubiquitous in microwave engineering because they are elegant, familiar to microwave engineers, and appropriate for many practical applications. However, they break down in highly nonlinear scenarios or in situations where the steady state can never be reached. In this paper, three examples illustrate the importance of using time domain approaches in such cases to preserve causality and to avoid drawing conclusions that conflict with the laws of Physics.