| Summary: | 碩士 === 國立中山大學 === 通訊工程研究所 === 103 === n recent years, the development of wireless communication system has grown rapidly. Long Term Evolution (LTE) can support wireless network to fast-moving mobile terminals. In this thesis, for stable and high data rate transmission in the railway wireless communication, vertically/horizontally dual-polarization omnidirectional multiple-input and multiple-output (MIMO) train antennas, which are mounted on the roof of high-speed rail trains, with dual-band 1.7~1.9 GHz and 2.5~2.7 GHz are presented.
First, an omnidirectional dual-band monopole antenna is designed for vertical polarization. In addition to co-designing antenna matching and antenna fixing mechanism, we also study the impact of ground plane on monopole radiation pattern. Secondary, to achieve omnidirectional radiation pattern in horizontal polarization similar to a magnetic dipole antenna, a loop antenna with a uniform and in-phase current distribution is required, but is difficult to design. Derived from Alford antenna design and multi-mode resonance, an omnidirectional broadband horizontally polarized antenna is designed. Furthermore, a dual-band horizontally polarized antenna is achieved by the self-supporting feed architecture and dual-band feed circuit design. Thirdly, we present omnidirectional dual-polarization dual-band MIMO antennas with an elliptical column size of π×91mm×51mm×61mm. The isolation for the proposed antennas is higher than 25dB at a small separation distance between antennas (~0.19λ_1.8GHz and ~0.26λ_2.6GHz, where λ_1.8GHz and λ_2.6GHz are the free space wavelength at 1.8 GHz and 2.6 GHz, respectively). Experimental and simulated results of the proposed antennas are presented and discussed. Finally, some omnidirectional horizontally polarized antenna applications are presented. Compared with the metal reflector, an omnidirectional horizontally polarized antenna on the top of electromagnetic band-gap structure (EBG) reflector has good return loss and radiation patterns. Moreover, an omnidirectional horizontally polarized antenna array is developed for base station applications.
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