Description of Electrically Small Resonant Antennas by Electric and Magnetic Dipoles

A new kind of field representation on the far field sphere is presented. This representation is based upon the polarisation states of the field. Polarisation states can easily be obtained upon determining the peculiar loci in the field. Depending on the polarisation state of the field, it is demonstrated that, either one of the magnetic or the electric dipole moments is dominant. Subsequently, criteria which may be applied to determine which dipole moment is responsible for the main radiation are derived. This characterization scheme which is a good figure of merit for an antenna designer may be useful in mobile communications especially in identifying possible adverse effects of RF fields on human health. The approach is also helpful for EMC engineers seeking to characterize and identify radiation sources of equipment under test.