power flux density (satellite comm.) (PFD)
Power Flux Density (PFD) is a measure of the electromagnetic radiation passing through a surface perpendicular to the direction of propagation.
It is specified in watts per unit area (W/m2), depends on the transmitting power and decreases with the distance of the measuring point to the antenna, namely quadratically to the distance. Thus, at twice the distance, the power flux density is only a quarter of the previous value.