A power wave theory of antennas

We introduce here a simple theory of antenna radiation and scattering that fully extends into the time domain a number of standard antenna terms, including gain, realized gain, antenna factor, scattering cross section, and radar cross section. The theory applies to antennas of all feed impedances and feed types, including waveguide feeds, and it applies to antennas embedded in any lossless medium. The approach is analogous to that used to describe circuits with generalized scattering parameters, which permits different characteristic impedances at each port. We identify receiving and transmitting impulse responses, and prove that they always have a simple relationship to each other. We also identify a scattering impulse response that can be applied to either an antenna or an arbitrary scatterer. From these functions, we build a Generalized Antenna Scattering Matrix (GASM). This establishes a formalism that allows one to calculate antenna response under a variety of conditions, including, for example, a mismatched source or load. The approach simplifies and clarifies terminology for characterizing antenna performance in the both the time and frequency domains.