Optimal space-time transmit signals for multi-mode radar

A structure is presented for constructing non-separable space-time transmit functions for multi-mode radar applications. By writing a space-time transmit signal as an expansion of space-time basis functions, transmit signal optimization can be reduced to simply finding an optimal set of complex weights. These weights form a data vector that can be determined for different optimization criteria, using linear algebraic techniques. Unfortunately, the optimality criteria where solutions are most easily found do not provide useful results for radar applications. Instead, mini-max or maxi-min criteria are often more applicable. An iterative solution for maximizing the minimum individual target-to-clutter-ratio is described, and results are presented. Moreover, the form of the resulting space-transmit signal is investigated, both at the transmitter and when incident on the illuminated targets. It is shown that the time-frequency spectrum incident on different targets can be dissimilar if true space-time transmit signals are applied. Different targets will then appear to be illuminated by different radar transmitters.