The multiple-input and multiple-output (MIMO) principle is a well-established method to improve the angular resolution of radars. Due to hardware limitations the maximum number of transmit and receive channels is often limited. In order to further increase the angular resolution with a given number of hardware channels, sparse arrays can be employed. However, the optimal placement of the antenna positions is a critical design parameter and it is difficult to consider non-idealities and mutual coupling within the design process. This paper addresses the non-idealities and the influence of coupling on the virtual array positions of a MIMO radar. An efficient calibration method to determine the real antenna positions is proposed. The discrete Fourier transform (DFT) based direction-of-arrival (DoA) estimation is shown with measurements of a 77 GHz and a 160 GHz MIMO radar for a uniform linear array (ULA) and two sparse arrays in comparison.