| Ultra-Wideband (UWB) antenna has experienced spark gap period, shortwave and TV times, and more recent period. Since Federal Communications Commission (FCC) authorized UWB for civilian and commercial application in 2002, UWB antenna has been widely studied and used in the area of various wireless communications. Compared with narrowband wireless communications technology, UWB has a lot of advantages such as high transmission rate, high safety, low interception rate and ambition performance of anti-multi-path attenuation. However, the UWB systems suffer from the interference of narrowband systems in indoor region because it overlaps with these narrowband systems. Recently, UWB antennas with band-notched characteristics have been reported by using different notch structures to suppress the potential interfered signals and to improve the performance of UWB antennas,which become a hot topic in both home and abroad. In addition, the Multi-Input Multi-Output(MIMO) systems can increase the capacity of the communication channel and speed up the signal transmission rate. Since MIMO antenna is a part of MIMO systems, the development of MIMO antenna with high isolation between the antenna elements has become one of hot research topics. This thesis mainly researches the band-notched UWB- and high isolation MIMO-UWB- antennas. The details of the research contents and results are as follows:Firstly, three band-notched UWB antennas with mini-sizes have been proposed to filter out the unexpected narrow-band interferences. At the beginning, a U-shaped resonator is used for integrating into a UWB antenna to suppress the interference from RFID frequency band which is operating at 6.8 GHz. Next, dual-band notched UWB antenna with meander lines etched in the radiation patch and ground plane is designed to eliminate the signals of Worldwide Interoperability for Microwave Access (WiMAX, 3.3-3.6 GHz) and Wireless Local Area Networks (WLAN, 5.15-5.825 GHz). Finally, a quad band-notched UWB antenna is proposed by using an arc-shaped slot on the radiation patch and a rotated E-shaped resonator beside the microstrip line. As a result, the designed antenna can coexist with WiMAX? WLAN(5.15-5.35 GHz and 5.725-5.825 GHz) and the uplink of the X-band satellite communications (7.9-8.4 GHz).Secondly, two MIMO-UWB antennas with identical antenna elements are proposed to achieve high isolation on the basis of UWB theory. These high isolation technologies are carried out by using inverted U-shaped branch loaded T-shaped stub and etching defected ground structure(DGS) which is implemented by three slots to reduce the coupling between antenna elements. The simulation results demonstrate that the MIMO-UWB antenna with inverted U-shaped branch loaded T-shaped stub has an isolation of -18dB, while the MIMO-UWB antenna with DGS achieves a low coupling of -20dB.Finally,we propose a MIMO-UWB monopole antenna with tri-band-notch function based on band-notch and decoupling techniques. This MIMO-UWB antenna is realized by using half circular monopole to cover entire UWB band. A protrude-shaped structure is inserted between the two antenna elements to change the current and, hence, it can reduce the coupling at low frequency. The tri-band-notch characteristic is designed by etching slots on the ground plane, adding anchor-shaped resonant on the radiation patch and a resonant ring with a gap. Simulated results show that the proposed MIMO-UWB antenna can not only provide three notch bands, but also achieve high isolation (S21<-20dB) except the low frequency band and 9.5 GHz. |
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