The recent emergence of personal sound zones applications investigates the development of acoustic solutions that generate spatial sound pressure level (SPL) contrast. While "active" electro-acoustic solutions using multiple sources do exist, another way to do so is to manipulate the acoustic field radiated from a baffled source using an acoustic lens. In this work, we propose a metamaterial based acoustic lens able to focus or steer an acoustic beam, using multiple slits loaded by periodic Helmholtz resonators. We control the acoustic radiation of a baffled duct by a meta-lens located at the output of the waveguide while excited at the other end by a plane-wave. A two-dimensional explicit model is developed, it is based on mode matching and accounts for thermo-viscous losses in the system. The pressure radiated by the meta-lens outside of the baffled duct is also explicitly calculated from integral formulations. The analytical results for near- and far-field radiation show excellent agreement with the solutions obtained by FEM. Finally, an optimal meta-lens is designed, for which the beam steering and focusing are reported experimentally on a 3D-printed prototype. This work paves the way of a complete analytical tool for optimizing the radiation of acoustic lenses using metamaterials.