Antenna efficiency is defined as the ratio of the aperture effective area, A e to its actual physical area, A . It describes the percentage of the physical aperture area which actually captures radio frequency ( RF ) energy.
12.
A station whose maximum coverage would otherwise be available at 4500 watts ( given a specific directional pattern and antenna system efficiency ) had a choice of either living with 2500 watts, or reducing the antenna efficiency to a level which would allow for 5 kW . Newly-constructed stations could fairly easily design an antenna system to meet the requirements, but stations on or moving to a shared tower with higher efficiency had a problem.
13.
Antenna gain \ scriptstyle G, which is equal to the antenna's directivity multiplied by the antenna efficiency, is defined as the ratio of the intensity \ scriptstyle I ( power per unit area ) of the radio power received at a given distance from the antenna ( in the direction of maximum radiation ) to the intensity \ scriptstyle I _ \ text { iso } received from an isotropic antenna at the same distance.
