Research On Broadband MIMO Antennas For Mobile Terminals

With the rapid development of wireless communication systems, the demand for businesstype and high data rate in mobile communication systems is increasing，and Scarce spectrumresources has become a bottleneck in the development of telecommunication. Withoutsacrificing additional spectrum or transmitted power in rich multi-path environments, MIMO(Multiple-Input Multiple-Output) technology has potentiality of increasing channel capacityand improving the quality of mobile communication systems.. As an integral components ofMIMO system for mobile terminal, MIMO antenna face the contradiction of limited spaceand amouts of antenna, the isolation between each antenna and the limited space, thebroadband feature and the size of antenna. Therefore, the design of broadband MIMO antennawith high isolation for mobile terminals has great significance.This thesis first shows the overview of basic antenna theory and the parameters used toevaluate the MIMO antenna performance, which establishes the foundation for further study.Then, a new broadband G-shape MIMO antenna with good isolation and compact size isproposed. This planar antenna has a bandwidth of100%with|S11|≤-10dB, from2.26to6.78GHz. The value of isolation between the two antenna elements is more than20dB in thewhole band. By adjusting two branches of the G-shaped antenna to make resonant modesclose each other which also can generate a new resonant mode, the broadband feature appare.We use the noval idea of combining two inverted L protrude branches and a T slot etched inground to reduce the mutual coupling.Furthermore, a new wideband slot MIMO antenna with multi-stubs loaded is proposed.the antenna has a wideband of1.68-3.83GHz with|S11|≤-10dB,|S21|≤-19dB. Theinnovation of the antenna is the method of expanding the bandwidth. Three pair narrow slotstubs are added under the orginal U antenna. Each loaded slot stub can generate a newresonant mode and then widen the bandwidth. The correlation coefficient of antenna is lowerthan0.1and the antenna is suitable for the application in LTE/WiMAX mobile terminals.Finally, a broadband uniplanar mobilephone antenna is proposed. The antenna has abandwidth of690-2230MHz with|S11|≤-6dB. The low frequency resonance is generatedby the grouded coupling branch and the pentagon monople can be used as a monopoleantenna, at the same time can be used as a driven branch. Through the common role ofmonopole antenna and coupling grounded coupling branch, antenna has a wideband feature.