| Within Ultra-wideband (UWB) technology is used for civil purpose in recent years, UWB technology has became one of the most competitive and promising technology in the future for its merits of high data rate, low system cost and multipath immunity. As an important part of the UWB system, design of UWB antenna has sparked much attention. Comparing with the traditional wideband antenna, design of UWB antenna encounters more challenges. Because it asks the antennas not only have wider bandwidth, but also to be compact, low-profile, and easy to integrate with printed circuit board. Meanwhile, within the UWB band, there exist some narrow communication bands, so it is necessary to avoid electromagnetic interference. The ability to integrate with filter in the antenna can significantly relax the requirements imposed upon the filtering electronics within the wireless device. The aim of the thesis is to design different kinds of antennas that meet the requirements of ultra-wideband systems and discuss varied approaches to improve the performance, broaden the bandwidth, decrease the size, and generate stopbands of the antennas.Chapter I briefly introduces the research background and application of the UWB communication technology and the UWB antenna, reviewed the developing history of UWB antenna. This chapter also illustrates the main job of this paper.Chapter II is attached more importance on several parameters to describe the performance of antennas, which include radiation principle, bandwidth, feed style and principle of generating stop-band. In addition, this chapter also introduced the numerical analysis methods of the UWB antenna.Chapter III is the most important part of the paper. First of all, this chapter introduces the planar monopole antenna. Base on studying large numbers of references, developments of the UWB planar slot antennas have been summarized, then, two planar UWB antennas with dual stopbands have been designed. At the peach-like monopole UWB antenna fed by microstrip, elliptical ground plane has been adopted to broaden the bandwidth of the antenna. Also the tapered feed line was used to match the impedance. As a result, the voltage standing wave ratio (VSWR) was evidently improved. At the CPW-fed monopole antenna of the diamond structure, the impedance bandwidth was broadened by using the circular transition structure. According to optimizing the parameters of the antenna, a novel diamond shaped UWB antenna with dual stopband characteristic has been designed.In chapter IV, two novel wide-slot antennas fed by CPW and Microstrip line have been designed. Impedance bandwidths of the antennas were broadened by adopting step-by-step transition feeding structure. Effects of varying the slot size on VSWR have been analyzed. The hybrid structure constituted of the elliptical and rectangular shapes has been adopted in the antenna design. Both of the antennas achieve the miniaturization and satisfy the FCC requirements of ultra-wideband standard. Finally in this chapter, the parasitical strip and the folded slot have been used to implement the dual band-notched characteristic.In Chapter V, a summary of the whole dissertation is given, and future research topics are suggested. |
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