4. (20 points) An antenna at r=0 radiates spherical waves with an electric field,
E=aϕEϕ + aθEθ, which has a radial dependence given by E(r,θ,ϕ)=E₀(θ,ϕ)h₀^(2)(βr), where E₀(θ,ϕ)=E(r,θ,ϕ) at some reference r, and h₀^(2) is the spherical Hankel function of the second kind. Consider the case of large r(βr≫1). Show that wave energy (or power) is conserved as the wave propagates outward.