COMPLEX-SPACE MULTIPOLE EXPANSION THEORY WITH APPLICATION TO SCATTERING FROM DIELECTRIC BODIES

Classical multipole theory, valid for radiation from sources with small dimensions, is extended to complex space. It is shown that by locating the multipole in complex space, the first terms in multipole series can be made more dominating than when restricting to real space. An expression for the complex location is derived to minimize the effect of the second-order multipole term. Using radiation from a phased cubic source as an example, it is seen that the radiating characteristic is an order of magnitude better for the dipole approximation when the dipole is in complex space instead of being at the center of the cube. Simultaneously, it is demonstrated that the validity of the dipole approximation is extended from L VM LS TH lambda to about L VM LS TH lambda /2, L being the measure of a side of the source. and lambda the radiation wavelength. Complex location for the electric dipole approximating a dielectric spherical scatterer is found through integral equation analysis corresponding to a linear approximation of the inner field of the scatterer.