| Since the Federal Communications Commission allowed 3.1GHz–10.6GHz unlicensed band for UWB communication, UWB technology have attracted researchers significant research interest due to their advantages, such as high data rate, low profile, good anti-interface ability. As an indispensable component in UWB system, UWB antennas should have the characteristics of compact size, simple structure, easy integration with monolithic microwave integrated circuits(MMIC), and ease of fabrication. So it provide the most promising solution for future short-range high-data wireless communications and many more applications. The research and design of UWB antennas are mainly focused on three aspects: the miniaturized radiation element, low envelope correlation coefficient(ECC) UWB diversity antenna, compact UWB antenna with band-notched characteristic. This thesis designs three kinds of antennas for UWB mobile communication systems. All simulations in this thesis are carried out by using the electromagnetic software Ansoft HFSS 15.0 and all measurements are carried out by Agilent N5230 20 GHz network analyzer. More details are listed as follows.Considering the integration of microwave circuits, the antenna miniaturization is one of the main metrics in UWB antenna design. Firstly, two methods of antenna miniaturization are proposed in this thesis, one is adding asymmetrical stubs extended from the ground plane, the other method is using an asymmetrical coplanar stripline(ACS)-fed structure which is cut prototype antenna half. And we design two simple and compact UWB antennas named as A1 and A2. The A2 is cut A1 half asymmetrically. The stub structures and microstrip feed line can improve the impedance mismatch caused by cut directly. Using the ACS-fed structure, the overall size of the proposed antenna A2 is reduced to 45% of the coplanar waveguide(CPW)-fed antenna A1. The simulated and measured results show that the overall performance and characteristic of the proposed UWB antennas operated at 3.1GHz-10.6GHz are very good, in which the return loss S11(S22)<-10 d B and VSWR<2.UWB systems suffer a lot from multipath fading. MIMO technology can be introduced into the design of UWB antenna to offer multiplexing gain and diversity gain to improve the channel capacity and link quality of UWB systems. Therefore, the design of UWB-MIMO antenna has great significance. The key point in design of UWB-MIMO antenna is to reduce the correlation between multiple antenna elements in a limited space. In this thesis, three UWB-MIMO antennas named as MA1, MA2 and MA3 with high isolation and low correlation between two UWB radiating elements are proposed. First of all, antenna MA1 radiation pattern is orthogonal by placing the antenna element orthogonal, and lower correlation is obtained. Secondly, antenna MA2 and MA3 also effectively achieve high isolation through adding decoupling structures, such as stubs and slots etched on plane, between two UWB radiating elements. The simulated and measured results show that the overall performance and characteristic of the proposed MIMO antennas operated at 3.1GHz-10.6GHz are very good, in which the return loss is S11(S22)<-10 d B and the high isolation is achieved(S12<-15 d B). The envelope correlation coefficient calculated between two elements shows consistent diversity performance is less than 0.15 across the whole UWB bandwidth. Thus, the proposed UWB-MIMO antennas are very suitable for portable UWB devices.The C- and L-shaped metal strips are added to ACS-fed UWB antenna A2 to plan a dual-narrow-band notched UWB antenna, and the Wi MAX(3.3GHz-3.7GHz) and WLAN(5.15GHz-5.825GHz) are excluded by the notched structures. The simulated results show it has a good dual-band-notched performace. |
