Applicability of Kirchhoff integral to antenna near fields

The physical interpretation and subsequent application of Silver´s formula to aperture fields containing surface waves is questioned. Using the more general Kirchhoff and Weber integrals, it is shown that the choice of the complex radial wavenumber k1 in these formulas must be consistent with the radial field decay; the formulas are therefore not applicable to composite fields having components with different radial decays. An antenna with a composite near field is described and the implications are discussed.