| The Federal Communication Commission (FCC) announced to open the permit of3.1-10.6GHz for commercial UWB application in February,2002. UWB systems haveattracted the academia and industrial attention for its advantages of high data rate, largeinformation capacity, low-power, etc. As is the case in conventional narrow wirelesscommunication systems, antennas in UWB systems also plays a very crucial role.There are some narrow wireless communication systems such as WLAN (WirelessLocal Area Network) operating at5.15to5.35GHz and5.725to5.825GHz andWiMAX (Worldwide Interoperability for Microwave Access) ranging from3.4to3.69GHz existing in the UWB frequency range. In order to avoid interference between thenarrow wireless communication systems and the UWB systems, the designed UWBantennas should have the band-notched characteristic in these frequency bands. Withthe rising and rapid development of the mobile Internet, mobile devices should notonly be able to transmit voice date, but also be able to transfer images and video data,which makes the already limited spectrum resource become more and more strained. Inorder to utilize the spectrum resource more effectively, the antenna that have themultiple-input-multiple-output (MIMO) characteristic is one of the future direction ofthe development.In this thesis, several novel UWB antennas are theoretical analyzed, simulated,optimized and actual tested. The main achievements of this work are as follows:(1) The definition, historical development, and the advantages of ultra-widebandare summarized. The development process and current status of the UWB antennadesign as well as various families of UWB antennas are reviewed. The issues related tothe UWB antenna design are expatiated.(2) The existing band-notched techniques are summarized and two kinds ofband-notched UWB antennas are designed according to them. In band-notched UWBantenna#1, through etching a slot on the right position of the radiation patch, whichnot only makes the basic UWB antenna achieve an extra2.4-2.484GHz Bluetooth butalso produces a notched band from2.52-3.66GHz. It can be applied in the devices which support both the Bluetooth and UWB protocol. The high frequency performanceis improved by cut two triangles away at the bottom of the radiation patch. A trapezoidsection has been etched on the ground plane to match the radiation patch’s resistancewith the microstrip feed line. Additionally, two split rectangular ring resonators (SRRR)are placed close to the microstrip line to reject the5.02-6.05GHz WLAN band. Inband-notched UWB antenna#2, the band-notched characteristic research is based onthe pervious designed inverted U-shaped slot UWB antenna working in the3-12GHz.By inserting a metal stub in the slot on the ground plane, a notched band from3.4-3.69GHz is achieved. The notched band from5-6GHz is obtained through etching aC-shaped slot on the radiation patch.(3) Two dual-polarized planar UWB antennas are designed. On the basis of theprevious studies, an isosceles right-angled triangle slot is used to design dual-polarizedUWB antennas. By introducing the novel structure, the antenna size can be reducedeffectively and the isolation between the two ports is improved while maintaining theantenna’s performance. The details of the design process are presented and thecorrelation coefficient between two ports is discussed. Improves are made based on thefirst designed antenna and the size of the antenna reduced further while the antennaperformance enhanced. |
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