How to reference antenna E-Field?

Hello All,

I have a question about incident electric field on an antenna. Suppose an electric field E_inc (for simplicity I am assuming this field to have only one polarization component - say V) is incident on a vertically polarized antenna. The current induced in the antenna will be E_inc x E_ant, where E_ant is the electric field of the antenna in the V polarization. My question is, with respect to what power level should E_ant be computed, since, unlike gain, the electric field strength is a function of the input power.

For e.g., in a ray tracing simulation, specifying the electric field at the transmitter w.r.t an input power level also implicitly specifies the transmit power. However when the incident field at the receiver is computed by the ray tracer, it is not clear to me how to specify the electric field level at the receiver.

Any thoughts on this would be deeply appreciated.

Thanks.