Broadband group delay waveguide lens

Abstract

A broadband group delay waveguide lens utilizing an array of half wave plates is disclosed. The lens is comprised of an array of uniformly spaced sections of waveguide having various lengths. The waveguide lengths are selected so as to provide an equal time delay to all rays from the focal point to the aperture plane of the lens. Since equal time delay does not ensure equality of phase at the aperture plane, half wave plates are inserted in the waveguide elements for adjusting the phase of each ray to obtain a constant phase plane over the aperture plane at the design frequency. The inner surface of the lens is spherical with the radius of the sphere equalling the focal length of the lens. The outer surface may be ellipsoidal having a semi-minor axis equal to the focal length and the semi-major axis is dependent upon the waveguide cross section dimensions and the design frequency. Such a lens has a low aperture phase error over a relatively large frequency range.