  We address the question of the optimal choice of loading material for antenna
miniaturization. A new approach to identify the optimal loading material,
dielectric or magnetic, is presented for resonant antennas. Instead of
equivalent resonance circuits or transmission-line models, we use the analysis
of radiation to identify the fields contributing mostly to the stored energy.
This helps to determine the beneficial material type. The formulated principle
is qualitatively illustrated using three antenna types. Guidelines for
different antenna types are presented.
