What is EIRP?

What is EIRP?

• A. The input power to the transmitter.
• B. The power loss in the feedline.
• C. The power actually radiated by the antenna element.
• D. The reflected power from the antenna.

Answer: (C)

EIRP is a way to express how strong the signal is in a specific direction by imagining an ideal isotropic radiator—one that radiates equally in all directions—would have to radiate to produce the same signal strength. It combines the power that actually makes it to the antenna input with how effectively the antenna concentrates that power in a given direction (its gain). In practical terms, this means the radiated power you’re considering in that direction—the power the antenna effectively emits toward that direction—is what EIRP is measuring. That perspective is why this option fits: it describes the power effectively radiated by the antenna element in that direction, which is what EIRP represents. The input power to the transmitter isn’t EIRP on its own, because losses along the feedline and the antenna’s gain determine how much actually makes it out in space. The feedline loss describes how much power is lost before reaching the antenna, not the radiated output. Reflected power from the antenna relates to impedance mismatches and standing waves, not to the radiated power in a direction.

EIRP is a way to express how strong the signal is in a specific direction by imagining an ideal isotropic radiator—one that radiates equally in all directions—would have to radiate to produce the same signal strength. It combines the power that actually makes it to the antenna input with how effectively the antenna concentrates that power in a given direction (its gain). In practical terms, this means the radiated power you’re considering in that direction—the power the antenna effectively emits toward that direction—is what EIRP is measuring. That perspective is why this option fits: it describes the power effectively radiated by the antenna element in that direction, which is what EIRP represents.

The input power to the transmitter isn’t EIRP on its own, because losses along the feedline and the antenna’s gain determine how much actually makes it out in space. The feedline loss describes how much power is lost before reaching the antenna, not the radiated output. Reflected power from the antenna relates to impedance mismatches and standing waves, not to the radiated power in a direction.