| With the rising and rapid development of the wireless communication, the increasing demands are moving towards large channel capacity and stable mobile radio link. Ultra wideband(UWB) technologies have enormous potential for many wireless applications, due to their advantages of large information capacity, high speed rate, anti-jamming, etc. In February, 2002, the Federal Communication Commission(FCC) announced to open the permit of 3.1-10.6 GHz for commercial UWB application. Multiple-input multiple-output(MIMO) technology is very applicable due to their advantages of decreasing channel fading which can effectually improve the transmission quality of the mobile terminals. By combining MIMO technology and UWB technology, and using multiple directional beams to obtain independent signals, it is available to obtain diversity gains and achieve remote transmission. As the absolutely necessarily element in wireless communication systems, antennas always play a very crucial role. There are some narrow wireless communication systems such as Wi MAX(Worldwide Interoperability for Microwave Access) and WLAN(Wireless Local Area Network) in the UWB frequency range. In order to avoid interference between the narrow wireless communication systems and the UWB systems, the UWB-MIMO antennas that have band-notched characteristics is one of the future directions of the development.In this thesis, several UWB-MIMO antennas are theoretical analyzed, simulated, optimized and actual tested. The main works are as follows:(1) The historical development and the advantages of ultra-wideband and MIMO technologies are summarized. The development process and current status of MIMO antenna design are reviewed. The issues related to the UWB-MIMO antenna design are expatiated.(2) The existing miniaturization techniques are summarized. A compact pattern diversity slot antenna for ultra-wideband(UWB) and Bluetooth applications is discussed. The ground plane is a 1/4 circular ring and two fork-like stubs are extended from the ground plane, which can be efficiently enhance the wideband isolation more than 15 d B. This proposed antenna operates from 2.3 to 12.5 GHz, which covers many different standards(Bluetooth, WLAN, Wi MAX, and UWB).And the two ports can radiate a vertical polarization wave and a horizontal polarization wave respectively. The other antenna is based on pattern diversity techniques and fed on the back of the antenna which can easily match with 50? load impedance. The presented antenna operates from 3.1 to 10.6 GHz and the isolation is more than 15 d B.(3) The existing band-notched techniques are summarized. Two UWB-MIMO antennas with band-notched characteristics are designed. The first one is etched a rectangular ring slot on the radiator to obtain WLAN band-notched. The antenna operates from 2.5 to 12 GHz, with a notched band from 5.1 to 6 GHz. The isolation is more than 15 d B. The other one is etched two circle rings on the radiator to achieve Wi MAX and WLAN band-notched characteristics respectively. This antenna operates from 2.2-12 GHz, with notched bands from 3.2-3.65 GHz and 5.2-6 GHz. The isolation is more than 15 d B. |
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