| With the rapid development of UWB systems in radar, navigation, electronic counter measures, secure communication and civilian field, it makes great requests in UWB antenna design as antenna is the critical component in UWB transmitting and receiving systems. Such as small size, low profile, broadband, high fidelity in time domain. In this paper, the author study and comprehensively analyze several kinds of UWB antennas both in frequency domain and time domain including some experimental results.The first and second chapters introduce the research background and significance, as well as the historical development and current situation of UWB antenna and UWB signal. The author also gives the definition and different forms of UWB signal, as well as the time domain characteristic and common different types of UWB antennas to enhance better understanding of UWB antenna design in time domain.The third chapter studies the design of small planar UWB antenna. In this chapter, the author designs three novel planar UWB antenna with small size and wide impedance bandwidth. The first type is a CPW fed ultra-wideband antenna. It uses semi-elliptic transformation of the ground plane and radiation patch to improve the impedance matching, which broadens the bandwidth of the antenna. In addition, the CPW fed antenna has symmetrical structure, which improves the antenna radiation pattern characteristics. The second type is a microstrip fed ultra-wideband antenna. It uses the method of rounding the keen vertexes on the radiation patch and defected ground structure with slot to change the current distribution and significantly improve the antenna impedance bandwidth. The third type is a planar bowtie antenna with resonant ring. The resonant ring outside of bowtie antenna can improve the low frequency impedance matching. The rounding of the keen vertexes can improve impedance bandwidth.The fourth chapter describes the design of UWB band-notched antenna. The author firstly introduces the research background of band-notched UWB antenna, then summarize the design methods of UWB band-notched antenna after reading majorities of literatures. Two innovative UWB band-notched antennas which designed by the author are discussed in details at last. The first band-notched antenna uses a tapered microstrip feeder line to improve the input impedance matching, by using a radiation patch which has an arc-shaped edge and a partially modified ground plane to make the current distribution more smoothly so as to enhance impedance bandwidth. By etching two nested U-shaped slots in the radiation patch, band-rejected filtering properties in the 3.5GHz WiMAX and 5.5GHz WLAN bands are achieved, so as to avoid the other communication bands interference to UWB system. The second band-notched antenna uses the technics of rounding the keen vertexes on the radiation patch and defected ground structure with slot to change the current distribution and significantly improve the antenna impedance matching. The impedance bandwidth is from 3.05GHz to 11.2GHz covering the UWB bandwidth of 3.1-10.6GHz. The total size of the antenna is only 24×30mm2, much smaller than other UWB antennas in many literatures. By using a vertical coupling strip, band-notched characteristic is acquired.The last chapter summarizes the main work and innovation of this paper, as well as the intending work. |
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