| Multiple-input-multiple-output (MIMO) systems are those that have multiple antenna elements at both the transmitter and receiver. MIMO system can provide radio channels capable of transferring parallel information within the same bandwidth, and greatly increase the attainable capacity. Currently,antenna design is still one of the important factors that make MIMO technology difficult to apply in mobile communications and 3G/B3G system. Along with the development of MIMO technology,the development of high-performance antennas for MIMO system is very urgent and will be also of theoretical significance and practical value.In this paper, the criteria for the diversity in MIMO system are generalized systematically. The application scenario of spatial diveristy, pattern diveristy and polarization diveristy are invesitgated. Then according to the requirement and characteristic of MIMO antenna design and also combined with the representative,novel and the latest MIMO antenna element and array used in communication system, we point out the development direction of the design and also bring forward the design principle and technology solutionLater,polarization diveristy MIMO antenna is deeply researched and designed. The author has designed and simulated the following MIMO diversity antenna which have excellent performance: dual polarization antenna, tri-polarization antenna, also pattern reconfigurable antenna with vertical polarization. Pattern reconfigurable antenna is a new idea for MIMO antenna design.Finally, the effect of antenna directivity on both spatial fading correlation and signal-to-noise ratio based on Kronecker channel model is investigated in three dimensional scattering environments. The channel capacity of multiple-in multiple-out system for uniform circular array, line array, and rectangle array is studied. The contribution of antenna directivity to channel capacity is concluded that, when the main lobe of directive antenna points at the coming wave, the improved signal to noise ratio resulting from the antenna directivity will exceed the negative impact caused by increased spatial fading correlation, leading to a better channel capacity than that of isotropic antenna. The stronger antenna directivity is, the greater the channel capacity. The results have both theoretical and practical value in analyzing and designing MIMO system transmit and receive antenna unit and array. |
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