Analysis And Design Of The Log-Periodic Antenna Applied In UWB System

The Log-Periodic Antenna (LPA) has been widely used for its splendid frequency independent performance since it was invented by the end of 50s of the 20th century. With the development of the material and technique, many forms of LPAs, such as the Log-Periodic Dipole Antenna (LPDA), have been developed and these antennas could match the different requests of different bands. In 2002, a part of UWB (Ultra Wide Band) band was approved to be used in civilian industries by FCC. And the UWB technology became a hotspot of the research of the LAN and other ultra-short wave communications. Now the approved UWB band ranges from 3.1GHz to 10.6GHz and the study of the antennas that could transmit short-pulse in this band without distortion is very important. The LPA is one of the candidates because of its frequency independent performance.In this dissertation, the UWB technology, UWB signals and antennas are introduced briefly at first. Next many forms of LPAs and the applications are presented. And then the LPAs and LPDAs that may be used as UWB antennas were simulated. Next the dissertation discusses the dispersive behavior of the conventional LPDA, which may cause distortion, and the method may solve this problem. Then the radiated and received signals with little distortion were gotten through using FDTD (Finite Difference Time Domain) method. Last, the configuration and parameters of the antenna are changed for better performance and smaller size.From the result, the return loss (S11) and radiation patterns match the request of UWB antennas. And the size could be reduced by many methods though LPDAs is one kind of the antennas which get wide-band at the cost of long structures. And from the result of the analysis with FDTD method, feeding the antenna at the larger, low-frequency end can improve the dispersive behavior of the LPDAs. Thus, this kind of LPDA analyzed in this dissertation may be used in UWB system.