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The design of a compact planar antenna featuring ultra wideband performance and simultaneous signal rejection in the 4-6 GHz band, assigned for IEEE802.11a and HIPERLAN/2, is presented. The design is demonstrated assuming RT6010LM substrate with a relative dielectric constant of 10.2 and thickness of 0.64 mm. The presented results show that the designed antenna of 27 mm 20 mm dimensions has a bandwidth from 2.7 GHz to more than 10 GHz excluding the rejection band. The antenna features near omnidirectional characteristics and good radiation efficiency. Index Terms-Planar antenna, slot antenna, ultra wideband (UWB) antenna.

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In the current quest for HTS films with negligible power effects at high RF power levels for wireless communications, accurate calculations of a maximum RF magnetic field H max and of a maximum RF current density J max flowing on the surface of superconducting films is necessary to allow for any sensible conclusions and comparisons. As the dielectric resonator method is used most frequently for investigation of HTS losses, the authors discuss in this paper a dependence of the circulating power and of a maximum RF magnetic field H max on dielectric resonators' geometry as well as of the maximum RF current density J max flowing on the surface of superconducting films on the films' thickness, for a general case of a resonator shielded in a metallic cavity. The authors' results demonstrate that under the same input power levels the same HTS films may be exposed to differing RF power level conditions, depending on the cavity to dielectric radius ratio and thickness of superconducting films. This means that there may be a significant discrepancy between calculated and real power handling capabilities of HTS films tested in different dielectric resonators unless correct formulas are used.

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