Equivalent isotropic response as a surrogate for incident field strength

The strength of an electromagnetic plane wave incident in the free field can be characterized in terms of power output by an idealized isotropic antenna probe. We refer to the parameter as equivalent isotropic incident power (EIIP), though it lacks an accepted name. This parameter has begun to enter use in various industry standards, technical reports, and peer-reviewed papers. To our knowledge, however, it has not been defined or studied in detail by prior work. We start to address this gap here with a proposed a definition, physical interpretation, and comparison to field strength.