  The recently introduced quantum particle swarm optimization (QPSO) algorithm
is employed to find infinitesimal dipole models (IDM) for antennas with known
near-fields (measured or computed). The IDM can predict accurately both the
near-fields and the far- fields of the antenna. A theory is developed to
explain the mechanism behind the IDM using the multipole expansion method. The
IDM obtained from single frequency solutions is extrapolated over a frequency
range around the design frequency. The method is demonstrated by analyzing
conductingand dielectric- type antennas. A calibration procedure is proposed to
systematically implement infinitesimal dipoles within existing MOM codes. The
interaction of the IDM with passive and active objects is studied through
several examples. The IDM proved to predict the interaction efficiently. A
closed-form expression for the mutual admittance between similar or dissimilar
antennas, with arbitrary orientations and/or locations, is derived using the
reaction theorem.
