| The thesis deals with the medium gain broadband omnidirectional antenna through those used as base or relay stations in WLAN system or mobile communications. Firstly, the research actuals of omnidirectional is outlined, the Method of Moments(MOM) and Finite Element Method(FEM) used in the analysis of antenna is introduced. Secondly, the technica of widening impedance bandwidth is discussed in detail, and several types of omnidirectional antenna structures are analyzed simultaneously using MOM and HFSS9.0. Thirdly, based on the theoretic analysis, a novel wideband omnidirectioanl planar antenna is presented, which can be easily fabricated on substrate and constructed with a lower cost. Finally, prototypes of the proposed antenna were constructed and studied. The presented x-band antenna shows a wide impedance bandwidth about 50%(VSWR<2), and a stable antenna gain level of about 6.5dBi, with small variations(δ<2.0dBi) for omnidirectional radiation, is obtained across the used bandwidth. Antenna design details and experimental results are proposed, which compared with excellent agreement. A constructed prototype performs well in actual project item. |
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