| Based on the development and application of the wideband omnidirectional antenna, this paper studies the methods of broadening the bandwidth and miniaturing the antenna’s size, and introduces the theory and application of the sleeve antenna in detail. Finally, three kinds of wideband sleeve antenna, a miniaturized sleeve antenna and a low profile wideband antenna are designed and discussed.First, this paper introduces the theory and development of omnidirectional antenna and the methods of broadening its bandwidth and miniaturing its size, and focuses on the theory and application of the sleeve antenna. Wideband, miniature and low-profile are the designing points. A ridged-sleeve antenna is presented first and adding symmetrical ridges can broaden its bandwidth. The second antenna is a capacitive circular patch sleeve antenna, loading a capacitance patch at the main radiator can broaden the bandwidth in the upper band. The third one is the capacitive annulus sleeve antenna, and loading a capacitive annulus can improve the bandwidth especially in the upper band. Then a miniaturized sleeve antenna is designed and discussed. The four antennas mentioned above have good radiation patterns and wideband characters. In chapter 5, a low profile antenna is designed and this antenna is based on the sleeve antenna, and some skills are used to lower its height and miniaturize its size. The low profile antenna, which has a small electrical size with wideband and omnidirectional characters are suitable for the airborne system.The third sleeve antenna is picked to be fabricated and measured, and the measured results match better with the simulated ones. |
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