| Recent evolutions in wireless mobile communications have shown that by employing multiple inputs and multiple outputs(MIMO)technology at both the transmitter and receiver,both the wireless system capacity and reliability can be enhanced without the need for increasing the power transmitted or using more spectrum.Despite a considerable amount of research have been done on the design of MIMO handset antennas,the design of low profile,small footprint and multi-standard(wideband or multiband)MIMO antennas on handset devices remains a challenging issue.Moreover,with the growing popularity of cell phones with full metal rim,the adverse effect brought by the metal rim on antenna design and performance must be carefully treated.In response to these needs and challenges,an in-depth research on MIMO handset antennas with metal rim is conducted in this dissertation.The main contributions are summarized as follows:Firstly,in combination with the evolutions of mobile communication technology and handset antennas,the research status and some difficult issues in the design of MIMO handset antennas with metal rim are introduced.Then,a new method used to analyze the resonant modes of handset antennas is proposed and the effect of metal rim on common types of handset antennas is analyzed.Subsequently,some current research on miniaturization,wideband and multi-band handset antennas are introduced.Some frequently used decoupling techniques and the performance evaluation criteria for MIMO system are also given.Based on the previous investigation,three MIMO antenna schemes are proposed.The first MIMO antenna is a 2×2 MIMO antenna system with reconfigurable elements based on metal rim.The width of the narrow side is only 5.5 mm,which is the highlight of this work and meets the requirement of current cell phones with big screen.By employing reconfigurable elements,the proposed MIMO antenna can cover seven WWAN/LTE operating frequency bands.Meanwhile,the performances of the system satisfy the MIMO standards.The second one is a 2×2 MIMO antenna system composed of two simple and compact parallel slots.By feeding them using an L-shaped coupled feedline and appropriate matching networks,multiple resonant modes of loops can be excited.The proposed antenna is capable of covering seven WWAN/LTE operating frequency bands.It overcomes the shortcomings of metal rim and maintains the integrity of the metal frame successfully.Meanwhile,the metal rim is only 5 mm in height.The compact size and unbroken metal rim are in line with the aesthetic needs of consumers today.The proposed scheme provides a solution for the design of a MIMO antenna with unbroken metal rim which is recognized as a difficult issue.The last one is a 4×4 MIMO antenna system operating in low frequency band.The antenna element is a slot antenna,which is easy to be integrated with metal rim.Slot elements of 2 mm in width are placed along the long sides of the ground board.Additional clearance is not required on the short sides of the ground board,which satisfies the trend of full-screen cell phones.By using an appropriate matching circuit,the system can cover GSM850/GSM900 operating frequency bands. |
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