Wavefront A wavefront is a locus where the field has constant phase e.g: E.0.)-F.(. Therefore the wavefront is defined by: arg(Eos)-Br=- If r is large and arg(E)is limited we have arg(Er)-Br≈-Br=-p→r= Therefore the wavefront is a spherical surface in our case.That's why it's called"spherical wave". Wavefront r Tx Ex (r,θ,ϕ) = E0 x (θ,ϕ) e− jβr r = E0 x r ej(arg(E0 x )−βr) A wavefront is a locus where the field has constant phase Therefore the wavefront is defined by: arg(E0 x ) − βr = −ϕ If r is large and arg(E0x) is limited we have arg(E0 x ) − βr ≈ −βr = −ϕ  ⇒  r = ϕ β Therefore the wavefront is a spherical surface in our case. That’s why it’s called “spherical wave”. e.g: