Design And Research Of Compact MIMO Antennas

As the mobile communication had a rapid development in recent years, the radiofrequency spectrum resources and transmit power, which can help to improve the data rates,have appeared to reach saturation. Therefore, Multiple-Input Multiple-Output (MIMO)technology, which significantly enhance the channel capacity and data rate without sacrificingadditional spectrum or transmitted power in rich scattering environments, has been proposedand has gradually become one of the core technologies of the fourth generation mobilecommunication system (4G).In MIMO system, MIMO antennas play an important role, since antenna can inherentlyinfluence the communication channel between transmitter and the receiver. At present,compact size, wideband operation and high isolation are open issues of the design of MIMOantenna. Especially, the design of a compact MIMO antenna for mobile communication,which includes all the difficulties, is important to not only MIMO system but also4G system.In this thesis, the design of a compact multiple-band and wideband MIMO antenna formobile communication has been studied. Three MIMO antennas with good performance areproposed, based on the research of MIMO antenna’s fundamental mechanism:1. A MIMO antenna with slitted ground. It is found that slitted ground is able tosuppress surface wave propagation, and thus reduce strong mutual coupling. Based on thestudy of slitted ground, this technique is extended to the design of a compact MIMO antenna.The antenna can provide two operating bands centered at2.70GHz and3.95GHz, coveringWLAN and WiMAX band respectively. The high isolation between antenna elements isachieved in both operation bands.2. A wideband slot MIMO antenna with stub-loaded dual-mode radiator. It is studiedthat stub-loaded radiator can create a second resonate mode, and thus along with thefundamental mode give dual-band even wideband operation. In order to explain themechanism well, an equivalent circuit is also given in the thesis. As examples, a dual-elementMIMO antenna with stub-loaded dual-mode radiator and a four-element MIMO antenna withstub-loaded dual-mode radiator are proposed. Moreover, these two MIMO antennas achieve low mutual coupling without adding any decoupling elements, since their antenna elementslocation and angular orientation are reasonable.3. A half-cut circular slot UWB MIMO antenna. It is found a miniaturization design ofa novel printed circular slot UWB antenna can be achieved by half-cutting method. By thisdesign of antenna element, a half-cut circular slot UWB MIMO antenna was proposed. Toimprove the input impendance matching and increase the isolation, a series of slits was etchedin the middle of ground.The simulated and measured results show the operation bandwidthcovers from3.10GHz to10.60GHz, and all the measure and calculated results show theproposed UWB MIMO antenna is a good cadiated for UWB MIMO system.