What does EIRP stand for, and how is it expressed for a satellite downlink?

• A. Equivalent Isotropic Radiated Power; EIRP(dBW) = Pt(dBW) + Gr(dBi) toward Earth.
• B. Effective Isotropic Radiated Power; EIRP(dBW) = Pt(dBW) + Gt(dBi) toward Earth.
• C. Environmental Isotropic Radiated Power; EIRP(dBW) = Pt(dBW) + Gt(dBi) + Antenna Efficiency.
• D. Effective Isotropic Received Power; EIRP(dBW) = Pr(dBW) + Gt(dBi) toward Earth.

Answer: (B)

EIRP stands for Effective Isotropic Radiated Power. It expresses the power that would have to be emitted by an ideal isotropic antenna to produce the same power flux in a given direction as the actual antenna does. For a satellite downlink, the relevant quantities are the transmitter power and the antenna gain toward the Earth. The EIRP in dBW is the sum of the transmitter power in dBW and the transmitter antenna gain toward Earth in dBi: EIRP(dBW) = Pt(dBW) + Gt(dBi). This reflects how the antenna concentrates energy in the Earthward direction compared to a perfectly isotropic radiator.

This is a transmitter-side measure, so the receiver’s gain does not enter the EIRP calculation. The term is not Environmental or Received Power, and antenna efficiency is not included in the standard EIRP expression.