Clutter rank for slow-time MIMO STAP

Multiple-Input Multiple-Output (MIMO) radar has been recently proposed to enhance performance compared to classical phased array. For STAP applications, coherent MIMO allows better angular resolution by using orthogonal waveforms. Several methods have been studied to generate orthogonal waveforms. We focus here on the slow-time waveforms which achieve orthogonality over the entire coherent integration time. We study in this paper the clutter rank using slow-time waveforms. We show that for certain cases the clutter rank cannot exceed a certain value and does not follow the Brennan rule. Some simulations are presented to illustrate this result.