Characteristics of half-volume DRAs with different permittivities

The development of small antennas for mobile phone handsets has been extensive during the last few years due to miniaturization of the handsets, employment of multisystem phones, and the requirements to reduce the RF power absorbed to the user. Traditionally monopole and helix antennas have been used in the handsets and lately planar antennas like patches or PIFAs have gained increasing interest. The basic problem in the development of handset antennas is to obtain fairly large impedance bandwidth (8-15%) combined with small size and possibly also with directivity. In some proposals this has been solved trivially at the expense of radiation efficiency by adding resistive loading to the antenna. The decrease of efficiency mainly due to conduction losses is also a general problem in the miniaturization of RF resonators used in filters and small antennas. Furthermore, it is known that waveguide resonators like dielectric resonators have typically relatively low conduction losses. Thus the half-volume dielectric resonator antenna (DRA) presented by Tam and Murch (see Electronics Letters, vol.33, no.23, p.1914-16, 1997) is an interesting candidate for a small antenna of mobile handsets. In this paper the properties of half-volume DRAs are studied as a function of permittivity (/spl epsiv//spl acute//sub r/=2-70). In addition to the normal characterization of impedance and radiation properties special emphasis is put also on the behavior of radiation efficiency of the antenna.