Which statement about EIRP is most accurate?

• A. EIRP equals the power that would be radiated by an isotropic antenna to achieve the same field strength as the actual antenna at the same distance.
• B. EIRP equals the received power at the antenna input.
• C. EIRP equals the transmitter power plus antenna gain.
• D. EIRP equals the transmitter power multiplied by the antenna efficiency.

Answer: (A)

Effective isotropic radiated power is the power that would have to be radiated by a perfect isotropic antenna to produce the same field strength at a given distance as the actual antenna in its main direction. It combines how much power you transmit with how well the antenna concentrates that power in a direction. In linear terms, EIRP equals the transmitter power times the antenna gain; in decibels, EIRP in dBW equals transmitter power in dBW plus antenna gain in dBi. This matches the idea of comparing to an isotropic radiator to produce the same field strength.

The other statements miss the key point: EIRP is not the received power at the input, it’s about the transmitted field strength in a direction; adding transmitter power and gain is not the correct linear relationship (though in dB the sum maps to multiplication), and efficiency alone doesn’t capture the directional effect that gain represents.