Far-Field Approximation of Electrically Moderate-Sized Structures by Infinitesimal Electric and Magnetic Dipoles

The far field (FF) of electrically moderate-sized structures can be reconstructed by a small number of infinitesimal electric and magnetic dipoles. As an example, the field of a current loop with a perimeter up to 1.5 lambda is approximated with two dipoles, the parameters of which are found analytically and using a genetic algorithm, respectively. The radiation of a rectangular power-ground plane pair is approximated by dipoles for various frequencies. The minimum number of dipoles needed for a good reconstruction depends on the complexity of the FF, and thus, on the electrical size, in terms of wavelength, of the structure. An estimate for the number of dipoles is given in the conclusion.