The design of a planar waveguide combiner of light beams, which performs the summation of a set of external light beams, is proposed. Combiner design options are considered and a 3D version with optical decoupling is proposed. The calculations of the operating parameters of the elements of the combiner depending on the values of the refractive indices of the layers of the structure are done. The minimum dimensions of the input/output diffractive elements of the combiner are estimated. Keywords: optical integrated circuits, optical beam combiner, diffraction grating, waveguide.