An apparatus comprises a dielectric material having a first surface and a second surface with a varying thickness between the first surface and the second surface. The first surface has a substantially hyperbolic curved shape with a single vertex, and the second surface has a substantially planar shape. The combination of the substantially hyperbolic curved shape and the dielectric material is chosen to compensate for different delays in electromagnetic waves impinging the first surface and traveling through the dielectric material such that the electromagnetic waves exiting the dielectric material through the second surface after traversing the dielectric material have a phase profile either constant or varying smoothly from the center to the edge.