Antenna directivity
= Antenna directivity
{title2=$D(\Omega)=4\pi U(\Omega)/P_{\rm rad}$}
The <antenna directivity> compares angular radiated power $U=dP_{\rm rad}/d\Omega$ with its average over directions. Its integral is $4\pi$. Unlike <antenna gain>, it uses radiated power rather than accepted input power, so it omits dissipative losses. A narrow beam can have high directivity without a larger total radiated power.