the radiation patterns considered were at distances from the aperture sufficiently large that all ray paths from the aperture to the field point are essentially parallel, i.e. r>a,b in Fig. 3.1 Here this assumption is removed and the radiation field in what is known in optics as the Fresnel zone of the aperture is examined. With the condition r > λ maintained, the reactive near fields of the aper ture are excluded from consideration.