The directive gain Gd(θ, 0) depends on antenna pattern. For the Hertzian dipole, Pavg is maximum at θ = \(\frac{π}{2}\) and minimum at θ = 0 or π. For an isotropic antenna, Gd(θ, ϕ) = 1. The directive gain Gd(θ, ϕ) can be defined as

Directive gain(G₀(\(\theta,\)\(\phi\))): An antenna measure how effectively it concentrates its radiated power in a specific direction.

(G0(\(\theta,\)\(\phi\))) = \(\frac{Radition intensity in the direction (\theta,\phi)}{Average radiation intensity over all directions}\)

• The directive gain is determined by comparing the strength of the radiation in the direction of maximum intensity to the average intensity over all directions.

Here, option 3 is correct.