Mismatched filtering for circulating space-time codes

For long range surveillance radars, space-time coding allows to increase the time on target (for improved Doppler resolution and classification capability), while still keeping a high resolution and accuracy in angle. The key performance for such systems is the sidelobe level of the ambiguity function, for which typical requirements are below 45dB. A new approach for optimizing the sidelobes level of such space-time coded active antenna systems is presented, and shown to allow very low sidelobes (-45dB, with 13 antennas and BT=257) over most of the range-angle domain, and a range profile with 35 dB dynamic range. This is achieved through an original mismatched filtering approach applied to Delft codes, which are space-time codes derived from circulating codes.