Bistatic coherent MIMO clutter rank analysis

The rank of the clutter covariance matrix in a bistatic coherent multiple-input multiple-output (MIMO) radar system with arbitrary planar arrays in both the transmitter and receiver is examined. The analysis provides further generalization of "Brennan´s rule" results available for linear arrays in monostatic coherent MIMO and bistatic space-time adaptive processing (STAP) systems. We first extend the two-dimensional (2D) monostatic STAP results of Varadarajan and Krolik (VK) to monostatic MIMO systems with planar arrays. We then use the VK bistatic STAP approach and determine conditions under which a four-dimensional (4D) bistatic MIMO system can be modeled as an equivalent 2D monostatic MIMO system, and apply the 2D results. The analytical expressions are validated against the numerically calculated rank of the theoretical clutter covariance matrix.