| In recent decades, with the rapid development of science and technology, radio equipment requires the development of high quality, high rate of transmission of information, broadband and source sharing. Wide band antenna as an important component has become an important branch in the field of antenna engineering. This thesis is devoted to improving the bandwidth of the antenna and reducing the size in VHF/UHF frequency band, and includes the following contents:1. Give an introduction to the VHF and UHF frequency band antennas.2. Through the research of whip antennas, conical antennas and microstrip antennas, and the help of wideband technology, this paper designs and produces a planar monopole antenna with an ultra-wide bandwidth for VHF and UHF bands applications. The dimensions of the antenna are 120cm×100cm×0.5cm. The measured and simulated results show that the antenna has a-lOdB return loss bandwidth from 65MHz to 1000MHz. The antenna is mainly omni-directional and has reasonable gain values over the operational band. Meanwhile, the antenna has vertical polarization. On the basis of the simulation and measurement results, the antenna has oo patterns in the elevation plane and omnidirectional patterns in the azimuth plane and a highest gain over the frequency band of 5.3dBi.3. Based on the antenna designed, the paper broadens the bandwidth to 30MHz and below by the use of optimizing the ground plane and the load resistance. The return loss of the antenna over across the band is less than-10dBi, except the band 52MHz-68MHz which is only under-8.5 dBi.4. Through further study of inverted cone antennas, by adding short columns and using load resistance at the end of them, the size of the inverted cone antenna can effectively be reduced, and the antenna is fabricated and measured. |
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