Abstract: Compared with the processing complexity of unit level co-located multiple input multiple output (MIMO) array, subarray level co-located MIMO array have more promising engineering applications. In view of the shortcomings of existing literature analysis based on cell level co-located MIMO array, the normalized antenna pattern function of co-located MIMO radar at subarray level is derived theoretically. Then, the essential differences in virtual aperture formation between subarray level co-located MIMO array and unit level co-located MIMO array is researched. The performance such as signal-to-noise ratio, angle measurement accuracy and angular resolution is compared between subarray level co-located MIMO array, cell level co-located MIMO array and phased array (PA) too. Finally, an experimental platform was built to verify the correctness of the theoretical analysis.