# Step 4-C: Computation of the Gain for a Single Direction

The antenna gain GP at point P is the quotient of the actual field strength and the field strength of the isotropic radiator at point P:

(1) $G=\frac{{|{E}_{ant}|}^{2}}{{|{E}_{iso}|}^{2}}=\frac{{S}_{ant}}{{S}_{iso}}$