MIMO Antennas For Mobile Phones

In recent years, with the rapid development of wireless communication systems, thedemand for high data rate and high quality mobile communication systems is increasing andthe conventional technologies of communication are difficult to solve this problem. Withoutsacrificing additional spectrum or transmitted power in rich multi-path environments, MIMO(Multiple-Input Multiple-Output) technology, which has potentiality of increasing channelcapacity and improving the quality of mobile communication systems, draws increasingattentions form scholars of mobile communication. MIMO technology has been extensivelyconsidered as one of the core technologies of LTE (Long Term Evolution) and4G (The fourthgeneration mobile communication system) systems. In LTE and4G systems, the MIMOphone antenna is vital and attentional. In the dissertation, the compact wideband/multi-bandMIMO antennas, which are suitable to apply in mobile phone, are studied, and several kindsof compact wideband/multi-band MIMO phone antennas with good characteristics arepresented. The dissertation was supported by the National Natural Science Foundation ofChina (61171029)“MIMO Antennas for Mobile Phones” and Guangzhou Science andTechnology Project (12C42081659)“MIMO Antennas for Mobile Phones”, and the maincontributions of the dissertation can be summarized as follows.(I) Based on the working mechanisms of monopole antenna and loop antenna, amonopole antenna is designed into a loop path through coupling, and stability or goodrobustness of phone antenna can be realized. Thus, with compact size, wide operation bandand good robustness, the monopole antenna is suitable as an antenna element for MIMOantenna. In the dissertation, the design proposal is applied in the design of a compactdual-band phone antenna, and the simulated and measured results proved the feasibility of thedesign proposal.(II) Based on the working mechanism of the two-strip, the dual-side two-strip are usedto compact the antenna size and improve the impedance matching of antenna, and antennassuitable for MIMO phone antenna are desinged. Based on the mechanism of mutual couplingbetween the antenna elements, methods to decreases the mutual caused by the ground surfacecurrents and space wave are analyzed in detail. Proposal and decoupling methods that mutualcoupling caused by the ground surface currents and space wave both can be reduced by onedecopling structure are presented, and the proposa and decoupling methods are applied in thedesigns of dual-band MIMO phone antenna with two antenna elements and Tri-band MIMOphone antenna with four antenna elements. The simulated and measured results show the two MIMO phone antennas have good properties, therefore, the proposal and decoupling methodsare feasible.(III) Based on the working mechanisms of decoupling and impedance mathing,structures, which can reduce the mutual coupling and improve the impedance matching ofantenna elements too, are investigated, and a kind of novel bent slits etched into the groundplane are presented. For the lower frequencies of the operation band, the function of the novelbent silts is the same as the conventional slits etched into the ground plane, the couplingcurrents flowing to the no excited port are blocked by the bent silts, and the isolation of theMIMO antenna elements can be improved. For the higher frequencies of the operation band,the novel bent silts can be considered as slit antennas, and they can produce resonant to widenthe impedance bandwidth. Moreover, the simulated and measured results show the effect ofthe bent slits on the impedance matching is slight.(IV) Based on the decouping mechanism of introdcution of additional coupling path,the neutralization lines are investigated to decrease the mutual coupling of MIMO phoneantenna with wide operation band, and a wideband T-shape neutralization line is proposed.The working mechanism of the wideband T-shape neutralization line is analyzed in detail, andthe simulated and measured results prove its feasibility. In order to cover the conventionaloperation bands of phone antenna and take advantages of the MIMO technology, a compactconventional phone antenna with operation band covering GSM900DCS PCS and UMTSis integrated with a wideband MIMO antenna, which operation band cover WLAN2.4WiMAX2.5and WiMAX3.5, and different decoupling methods are applied to improve theisolation for the different kinds of antenna elements.(V) Based on the adventanges of UWB (Ultra-Wideband) antenna technique and MIMOantenna technique, the combine of the two kinds of antenna techniques is proposed. Theinteractions of decoupling structure and band-notched structure are studied in detial, and acompact dual band-notched UWB MIMO antenna with high isolation is designed successfully.In the design, a special layout of the two antenna elements is realized by the application oftwo protruded ground parts, which can improve the impedance matching, reduce the size ofantenna element, increase the distance (along the ground plane) between the two feed ports,and lower the mutual coupling. A metal strip is placed behind the antenna element. Bycoupling beweent the metal strip and the antenna element, a coupling loop path is producedfor the band-notched frequency. Without increasing the sizes of antenna elements, thisband-notched structure does not increase the mutual coupling between the two antenna elements.