Optimal Antenna Matching and Mutual Coupling Effect of Antenna Array in MIMO Receiver

Hiroki IURA  Hiroyoshi YAMADA  Yasutaka OGAWA  Yoshio YAMAGUCHI  

IEICE TRANSACTIONS on Communications   Vol.E90-B   No.4   pp.960-967
Publication Date: 2007/04/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.4.960
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Antennas and Propagation
MIMO,  mutual coupling,  antenna matching,  channel capacity,  correlation,  

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Antenna array is essential factor for multiple- input multiple-output (MIMO) wireless systems. Since the antenna array is composed of closely spaced elements, the mutual coupling among the elements cannot be ignored for the best performance of the array. Mutual coupling affects the MIMO channel, so the performance of a MIMO system, including channel capacity and diversity, varies with the degree of mutual coupling. The effect of mutual coupling is a function of the antenna load impedance. Therefore, designing an optimal element-matched array for a MIMO system requires consideration of the optimal matching condition for the array elements, the one that maximizes the channel capacity. We evaluated the effects of mutual coupling with various matching conditions in dipole arrays, and investigated their effects on the path correlation and channel capacity of MIMO systems. Simulation showed that the conventional conjugate matching of each element is still suitable for closely spaced elements except when the separation is about less than 0.1λ. Theoretical consideration of the received power of a closely-spaced-element array is also provided to show the effects of mutual coupling.