Miniature dielectric-loaded personal telephone antennas with low SAR

The short history of the cellular telephone have witnessed astonishing advances in the state of the art of personal telephone handset design. However, there is an increase in the public anxiety about possible health risks of using personal telephones, and it is becoming increasingly important to produce handsets which completely meet the international specific energy-absorption rate (SAR) regulations. The most common antenna topologies used on handsets today are basically monopole or monopole derived structures. One significant limitation of monopole and some monopole derived antennas concerns their lack of polarisation diversity. Personal telephone handsets are often used inside buildings and in urban environments where scattering of the signal from vertically and horizontally disposed surfaces promote mixing of polarisations which changes spatially. Moreover the orientation of the handset with respect to the dominant polarisation plane of the base-station antenna can be entirely arbitrary. Efforts have been made to propose “figure of merit” measures for mobile telephone antennas in cluttered urban environments. This article shows that antennas with high diversity have superior communications performance