Abstract: A diverging shall antenna fed by a waveguide supplying TE.sub.11 mode is described. A dielectric rod partially contained within the waveguide converts the TE.sub.11 mode to a dominant or HE.sub.11 mode. The HE.sub.11 mode is controllably converted to second and third order modes in the diverging shell by discontinuities placed in predetermined locations in the diverging shell. The discontinuities generating the second mode are incorporated into the dielectric rod structure. Turning of the relative amplitude and phase of the second and third order modes relative to the HE.sub.11 mode is achieved by slideably positioning the dielectric rod. An alternative embodiment of the inventive device includes a reactive surface of the diverging shell.

Abstract: A dielectric inset mountable within a conical horn antenna for focusing an impinging electromagnetic wave front as a planar wave front at an attached wave guide. In one construction a homogeneous inset having an ellipsoidal forward surface and conical aft surface is fitted into a double flared conical antenna including a cylindrical, hybrid mode matching section. In various alternative compound constructions, materials of differing dielectric constants and geometrical shapes are arranged to facilitate a size and weight reduction of the inset and focus the incident wave front relative to the wave guide. In other embodiments, still lower density materials, including suspended metallic particulates are used.