Power Flux Density

Power flux density (PFD) is a measure of the power from a radio transmitter incident on a surface, expressed as power per unit area, typically in watts per square meter (W m^–2) or in decibel watts per square meter (dBW m^–2). In satellite communications, PFD is used to characterize the strength of a satellite signal at the Earth’s surface or at another receiver location, independent of the receiving antenna characteristics.

PFD is related to the satellite’s effective isotropic radiated power (EIRP) and the propagation path loss between the satellite and the point of interest. It provides a convenient metric for assessing interference potential and regulatory compliance, as it describes the electromagnetic energy density arriving at a given location rather than the power captured by a specific antenna.

PFD is a key parameter in international frequency coordination and spectrum management. Regulatory limits on PFD, defined by the ITU in the Radio Regulations, are used to protect terrestrial services, other satellite networks, and radio astronomy from harmful interference, particularly for non-geostationary satellite systems operating over wide geographic areas.