Spherical-wave characterization of interior and exterior sources

This paper presents the theoretical basis for spherical, near-field scanning in the general case where radiating sources exist both inside and outside the measurement region. The fields are expanded in terms of outgoing spherical waves (due to interior sources) and standing spherical waves (due to exterior sources). Additional information is required to solve for the increased number of unknowns, and results for the spherical-wave coefficients are derived in terms of the tangential electric and magnetic fields on the surface of a sphere. The special case of an electrically small emitter is examined in detail, and several formulations are presented for the equivalent electric and magnetic dipole moments.