Causality and waveguide circuit theory

We develop a new causal power-normalized waveguide equivalent-circuit theor y that, unlike its predecessors, results in network parameters usable in bo th the frequency and time domains in a broad class of waveguides, Enforcing simultaneity of the voltages, currents, and fields and a power normalizati on fixes all of the parameters of the new theory within a single normalizat ion factor, including both the magnitude and phase of the characteristic im pedance of the waveguide. Enforcing simultaneity also ensures that the theo ry's voltages and currents do not start before their excitation, and that t he network parameters of passive devices are causal, a necessary condition for stable time-domain simulations.