A dielectric cone radiator sub-reflector assembly for a reflector antenna with a waveguide supported sub-reflector is provided as a unitary dielectric block with a sub-reflector at a distal end. A waveguide transition portion of the dielectric block is dimensioned for insertion coupling into an end of the waveguide. A dielectric radiator portion is provided between the waveguide transition portion and a sub-reflector support portion. An outer diameter of the dielectric radiator portion is provided with a plurality of radially inward grooves extending radially inward to a diameter less than an inner diameter of the end of the waveguide and a lens bore extends from a proximal end of the dielectric block towards the distal end of the dielectric block at least to the sub-reflector support portion. The unitary dielectric block may be manufactured as a single contiguous monolithic portion of dielectric material via injection molding.