Abstract: A rear feed assembly for a microwave aerial, comprising a dielectric support member having an energy reflecting surface positioned against one face thereof. Waveguide means is connected with the support, the center of the waveguide aperture being the phase center of the assembly and the said face of the support being located in the far field region with respect to that center. The support is so shaped that energy emitted from the waveguide means is reflected from the reflecting surface and emerges through a second face of the support with a spherical wavefront centered on the image phase center.