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The efficiency-bandwidth product (EB) is used in the evaluation of small dielectric loaded monopole antennas (DLMAs). The EBs of the DLMAs have been precisely measured on the basis of the Wheeler cap method. As a result, an improvement in the EB of electrically small cylindrical DLMAs has been confirmed experimentally in comparison with that in a bare monopole antenna. In addition, within the category of electrically small antennas considered here, it seems that there exists an optimum value of permittivity for the dielectric loading for which the best EB value is obtained.
Introduction: Dielectric loaded antennas (DLAs) [1 - 4] have been studied analytically and experimentally for many years. Currently, there are many applications for such small communication devices in cellular telephones. The use of a dielectric in antennas mainly contributes to a size reduction while the operating frequency is maintained. Moreover, an enhancement of the antenna performance is expected if the appropriate permittivity and shape of the dielectric loading are chosen.
In general, the performance of antennas has been evaluated by such a conventional criterion as gain, efficiency or bandwidth. For electrically small antennas, the use of Wheeler's PF (radiation power factor) [1, 2] and the efficiency-bandwidth product (EB) [3] has been suggested. Enhancement of the PF by dielectric loading was analytically predicted in [2] where an investigation into the use of a small dipole antenna loaded with a dielectric sphere is presented. The PF in [2] can be regarded as equivalent to the EB. Experimental studies have, however, rarely been reported for the EB of such electrically small DLAs.
In this Letter, we present an experimental investigation into the possibility of obtaining an improvement in the EB of the DLAs, by changing the value of permittivity of the dielectric loading. In particular, cylindrical dielectric loaded monopole antennas (DLMAs) with the same physical volume are used as the DLAs.
Formulation of EB: Smith [3] showed that, in a capacitative antenna, the EB is equal to the radiation resistance of the antenna divided by its input reactance:
(ProQuest: ... denotes formula omitted.)
where Rr, Rloss and X are the radiation resistance,...