For an infinitesimally small dipole in free space, the electric field Eθ in the far field is proportional to (e⁻jkr/r)sinθ, where k=2π/λ. A vertical infinitesimally small electric dipole (δl≪λ) is placed at a distance h (h>0) above an infinite ideal conducting plane, as shown in the figure. The minimum value of h, for which one of the maxima in the far field radiation pattern occurs at θ=60°, is