The surface equivalence principle is heavily used in the analysis of antenna problems to simplify the problem: in many of the applications, the close surface is chosen as so to encompass the conductive elements to alleviate the limits of integration. Selected uses in antenna theory include the analysis of aperture antennas and the cavity model approach for microstrip patch antennas. It has also been used as a domain decomposition method for method of moments analysis of complex antenna structures. Schelkunoff's formulation is employed particularly for scattering problems.