Study Of Compact Planar Ultra-wideband Antennas

Since the Federal Communications Commission (FCC)'s allocation of the frequency band of 3.1-10.6 GHz for commercial use, ultra-wideband (UWB) system has attracted significant research power in the wireless communication field. As one of main issue of UWB system, the characteristics of the antenna will influence the performance of the whole system. Therefore, the researches on UWB antennas are meaningful and valuable.The UWB antennas are employed to transmit/receive time-domain pulse signals, so the time-domain characteristics of the UWB antennas are very important. In this paper, a simplified modeling is proposed and demonstrated for UWB antenna time-domain analyses, so the time for simulation can be greatly reduced. Moreover, correlation factor and pulse width stretch ratio (SR) are resorted to estimate the time-domain characteristics of the UWB antennas.By analyzing the current distribution of the UWB antenna, the portions with little current distributed can be cut off and the rest portions can be curved to decrease the dimensions. To lower the first resonant frequency, the current path at low frequency should be extended, the antenna can be miniaturized as a result. Depending up the thinking, two UWB antennas with compact sizes have been designed.Over the whole UWB band, there are some other wireless communication systems (WLAN and WiMAX), so it is necessary to minimized the interference between them. It can be achieved by introducing notched band in UWB antennas. In this paper, one and dual notched bands have been implemented by etching slots in the radiator and ground plane of coplanar waveguide fed (CPW-Fed) UWB antennas and UWB slot antennas. The effects of varying the length, width and location of the slots have been analyzed fully. To optimize the band-notched function, two ways have been proposed. One is by integrating a bandstop filter with an UWB antenna, the other is by adding the resonant frequencies in the required notched band. Both can be used to achieve controllable notched-band with high rectangle factor.