In order to study the impacts of array configuration and channel model parameters including antenna spacing and scattering angle on the channel capacity of a MIMO (Multiple Input Multiple Output) system, a novel method is proposed to explore the channel capacity under flat fading. Fading correlation matrix is constructed based on uniform circular antenna and uniform linear antenna at the receiver side, respectively. And then using the properties of Wishart distribution, closed-form expressions for the upper and lower bounds on the ergodic capacity of N by M MIMO system are presented in detail. The problem of calculating the probability density function of eigenvalues of the fading channel matrix is avoided and the computational complexity is lower in contrast to the previous methods. The novel method also could be generalized to MIMO-OFDM systems with any number of transmit and receive antennas. Computer simulation results show that for small spacing the UCA yields higher channel capacity than ULA. The channel capacity is maximized when the antenna spacing increases to a certain point, and further more, the larger the scattering angle, the quicker the channel capacity converges to its maximum. And at high SNR, the upper and lower bounds on the ergodic capacity are close to its true value.