| has gloss | eng: In electromagnetics, directivity is a figure of merit for an antenna. It measures the power density an actual antenna radiates in the direction of its strongest emission, relative to the power density radiated by an ideal isotropic radiator antenna radiating the same amount of total power. Mathematically, the directivity is defined as the maximum of the directive gain: :D = \max\left(\frac\mboxRadiated power density}\left(\theta,\phi\right)}\mboxTotal radiated power}/\left(4\pi\right)}\right) where *\theta and \phi are the standard spherical coordinates angles *Radiated power density is the power per unit solid angle such that \mboxTotal radiated power}=\int_\phi=0}^\phi=2\pi}\left(\int_\theta=0}^\theta=\pi}\mboxRadiated power density}\left(\theta,\phi\right)\sin\theta\,d\theta\right)d\phi *4\pi is the total solid angle for a sphere (also the surface area of a unit sphere, similar to 2\pi being the total angle for a circle and the perimeter of a unit circle). |
