Antenna effective area
= Antenna effective area
{title2=$P_{\rm av}=A_{\rm eff}S$}
The <antenna effective area> converts incident <energy flux> into available received <power> for a specified direction and matched <polarization of an electromagnetic wave>. In a lossless free-space link, a transmitter of <antenna gain> $G$ at range $r$ and a receiver of effective area $A_{\rm eff}$ have $P_r/P_t=GA_{\rm eff}/(4\pi r^2)$. Impedance or polarization mismatch reduces the delivered power.