Source:FERMAT, Articles, 2016-Vol15-May_Jun-002
Abstract:Conducting antennas are often coated with insulating materials to minimize the environmental effects, or prevent electrical shorting in conducting media. In most cases the coating material is too thin, with respect to the wavelength, to cause appreciable changes in the antenna performance. However, in electrically large antennas, or at high frequencies, the coating thickness can be sufficient to cause resonances that can influence the antenna performance. Previous studies have shown enhanced power radiations due to such resonances. This article is aimed at reviewing such cases and providing proper explanation of the resonance phenomena and the resolution of anomalous power radiations. To make the problem more realistic, yet analytically solvable to prevent computational errors, spherical dipole antennas are selected and solutions are developed for both single and double coating configurations. In the former case, only material coating is considered, and a parametric study in performed to investigate the resonance effects on the antenna performance and radiated power, as well as, the directivity. However, in the latter case the material and metamaterial pairs can cause additional resonances, and their combination is used for a comprehensive study of the coating effects. It is shown that the cause of the anomalous power radiation is the use of idealized sources that leads to incorrect interpretation of the results, rather than the enhanced power radiation due to the coatings. It is also shown that the phenomenon is the same for both natural materials and metamaterials, providing identical results.
Index Terms:Spherical antennas, Coated antennas, Resonant modes, Metamaterials, Power enhancements, Anomalous power radiation.
View PDFResonance Effects in Material and Metamaterial Coated Antennas and Resolution of Anomalous Power Radiations