The conditions under which the information inside each subcell of a two-dimensional (2D) object, periodic in orthogonal directions, is replicated throughout all the subcells of the unit cell are obtained. Relative-phase relationship among all the subcells depends only on the number of subdivision but not the length-to-width ratio of the unit cell. From this relationship, the wave amplitude at all the subcells is calculated by superposition of the information from all the subcells in the original object. A 2D object periodic in nonorthogonal directions can be decomposed as a set of laterally shifted 2D objects which are periodic in orthogonal directions. Hence, the image formation problem for nonorthogonally periodic object can be solved directly from the superposition of results for the laterally shifted, orthogonally periodic ones.
