El área efectiva de cualquier antena ya sea emisora o receptora, se define para la condición en la que la antena se usa para recibir una onda electromagnética plana polarizada linealmente. El área efectiva se define como la relación entre la potencia recibida y la densidad de potencia incidente en una antena.
(Ítem A )(formula 2 y 3)
The effective area of any antenna, whether transmitting or receiving, is defined for the condition in which the antenna is used to receive a linearly polarized, plane electromagnetic wave. The author suggests the adoption of the following definition:
Where Pr is the received power as defined above and Po is the power flow per unit area of the incident field at the antenna. In words, (3) states that the received power is equal to the power flow through an area that is equal to the effective area of the antenna. Note that the definition does not impose the condition of no heat loss in the antenna. Equation (3) shows that the effective area of an antenna is proportional to its power gain. The effective areas of antennas of special interest are given in the following: