Directivity

Directivity is a measure of the extent to which a radiator throws power more in one direction than others. To find the directivity at a given

azimuth and zenith, the target is placed in this direction, and the quotient dP/dA is constructed, where dP is the power incident on the target

and dA its area. dP/dA is normalized by division with the isotropic power level of the radiator at this range, to eliminate dependance on power level.

dP/dA is approximateley equal to the Poynting vector at the center of dA.

The directivity of the radiator is estimated using both dA and dO.

The range of the target is increased to 10 wavelengths. Estimates of directivity converge.

dA is reduced in sized to secure convergence of dP/dA and dP/dO to theoretical value. 1.64.