In this paper we propose a nanoscale planar lens structure for generating Bessel beam like fields to achieve large focal lengths and depth of fields. The structure consists of sub wavelength slits of different widths constructed on a thin metallic slab that is surrounded by air on both sides. The proposed structure is simulated using a modal technique that represents the structure as a waveguide and solves for the modes of the waveguide. Although diffraction affects the behavior of the generated beam from that of conventional Bessel beams, the simulation results show that the proposed structure is very promising for obtaining a very compact Bessel beam generator.