On the Cylindrical and Spherical Waves Spectral Contents of Radiated Electromagnetic Fields

General expressions for the cylindrical and spherical wave expansion coefficients of the field of an arbitrary antenna are determined, using the dyadic Green's function, expanded in the appropriate vector waves. The upper limit on the amplitudes of these coefficients yield simple expressions for determining the largest number of significant harmonics expected in the field. This number is found to be potentially large very close to the source and decreases with distance from it. The evaluated amplitude of the harmonics in the fields of practical antenna models validates the establish criterion and demonstrates the inadequacy of existing guidelines.