ANTENNA DESIGNERS have long been faced with the challenge of miniaturizing their components. Resonant antennas that are typically used in hand-held wireless devices can be made geometrically smaller by inserting the appropriate loading material into the structure. But filling an antenna with material will change its field distribution. Antti O. Karilainen, Constantin R. Simovski, and Sergei A. Tretyakov of the Department of Radio Science and Engineering of Aalto University (Aalto, Finland) and Pekka M.T. Ikonen with TDK-EPC (Espoo, Finland) pondered the issue of identifying whether a dielectric or magnetic material would be the optimal loading material to optimize the bandwidth of a miniaturized design.
The researchers used the analysis of radiation mechanism to identify the fields contributing mostly to the stored energy in different miniaturized antenna designs to determine the more beneficial material type. They explored their approach using a dipole antenna and a patch antenna, as well as a planar inverted-L antenna where the conventional analysis of a circuit or a transmission-line resonator yields incorrect conclusions.
By analyzing the radiating fields for each antenna type, it was possible to select the best filling material for miniature resonant antenna designs. If the radiation mechanism is equivalent to an electric current, dielectric material works better for loading. If the radiation mechanism is equivalent to a magnetic current, magnetic loading material is the proper choice. See "Choosing Dielectric or Magnetic Material to Optimize the Bandwidth of Miniaturized Resonant Antennas," IEEE Transactions on Antennas and Propagation, Vol. 59, No. 11, November 2011, p. 3991.
