Spherical and plane waves spherical wavefront Spherical wave 下=ri (.6,p)=E。(0,p), In far field a spherical wave can be locally approximated with a Plane wave E(,0,p)≈E,e with E E(6,9 k=Bi, ≈plane wavefrontSpherical and plane waves Tx spherical wavefront Spherical wave  E(r,θ,ϕ) ≈  Eo (θ,ϕ) e− jβr r r = rˆ ir with  Eo ' =  Eo (θ,ϕ) r k = βˆ ir In far field a spherical wave can be locally approximated with a Plane wave  E (r,θ,ϕ) ≈  Eo ' e− j ki r ≈ plane wavefront k e