A Novel Square Antenna Array to Improve the Capacity Stability of 4-Element Compact Mimo Systems

In a compact multiple-input-multiple-output (MIMO) communication systems, the channel capacity of a traditional 4-element uniform linear array (ULA) will decrease rapidly with the increment of the mean angle of arrival (AoA) of the incident waves. We will show first in this paper that this channel capacity decrement is caused by the antenna radiation pattern distortion, which owes to the so-called mutual coupling (MC) effect among the dense array elements. In order to overcome this channel capacity decrement flaw of ULA, a 4-element square antenna array (SAA) with space symmetric structure is proposed by re-arranging the antenna elements layout according to the idea of reducing the final radiation pattern distortion. Three-dimensional capacity matrix eigenvalue distribution and generalized condition number (GCN) are also developed in this paper to analyze the final capacity stability of 4-element compact MIMO systems. Theoretical analysis and numerical simulations show that comparing with the traditional 4-element ULA, the new 4-element SAA with space symmetry is much less sensitive to the AoA of incident waves, and can maintain a more stable channel capacity.