The modal properties of a laser resonator consisting of an array of sources and a diffractive mode-selecting mirror are presented. The modal discrimination is optimized by selection of cavity parameters, and can be enhanced by additional diffractive elements. We find that the modal properties differ significantly from a conventional Talbot cavity. Because of the diffractive mode-selecting mirror, these are virtually no edge effects and the fundamental mode loss is very small. The modal discrimination is maximized at a round-trip cavity length of both one-half and one Talbot distance. There is an optimum array fill factor that depends on the cavity length and the array size. Finally, if the cavity length and fill factor are optimized, there is no loss of discrimination with increasing numbers of elements in the array.