Abstract: Considering that the channel capacity of a uniformly linear array (ULA) will decrease rapidly with the increasing of mean angle of arrival (AoA), this paper provides a squared antenna array (SAA) with symmetric structure. Based on the precisely derived expression of array element mutual impedance (MC), the influence of MC on the spatial correlation and multiple input and multiple output(MIMO) channel capacity of SAA are first analyzed; then the stability of the channel capacity of ULA and SAA are also compared in the case of uniformly distribution of power azimuth spectrum (PAS). Theoretical analysis and numerical simulations show that this symmetric SAA can provide more stable channel capacity than the traditional linear array ULA due to its complementary properties among the antenna array elements, suggesting that it is more suitable for the actual communication environments.