To the best of our knowledge, in this paper, a new technique is presented for designing and analyzing inhomogeneous flat lenses. The technique is based on the critical angle theorem. Slab and wedge lenses are presented in this manuscript. The designed lenses are frequency independent, so they operate in the broadband frequency bandwidth. The method presented here can be generalized to all inhomogeneous structures, and the input and output layers of the proposed flat lenses are impedance-matched to the circumference. The proposed lenses are validated with COMSOL multiphysics.