Space-Time Adaptive Processing (STAP)

Space-Time Adaptive Processing (STAP) is a signal processing technique that enhances the ability of radars to detect targets that might otherwise be obscured by clutter or by jamming. To implement STAP requires sampling the radar returns at each element of an antenna array, over a dwell encompassing several pulse repetition intervals. The output of STAP is a linear combination or weighted sum of the input signal samples. The "Adaptive" in STAP refers to the fact that STAP weights are computed to reflect the actual noise, clutter and jamming environment in which the radar finds itself. The "Space" in STAP refers to the fact that the STAP weights (applied to the signal samples at each of the elements of the antenna array) at one instant of time define an antenna pattern in space. If there are jammers in the field of view, STAP will adapt the radar antenna pattern by placing nulls in the directions of those jammers thus rejecting jammer power. The "Time" in STAP refers to the fact that the STAP weights applied to the signal samples at one antenna array element over the entire dwell define a system impulse response and, hence, a system frequency response. The clutter spectrum seen by ground based radars typically has a ridge at zero Doppler while the clutter spectrum seen by airborne radars is typically more complicated due to the combination of platform motion and antenna pattern. STAP processing adapts the radar frequency response to the actual clutter spectrum in which the radar finds itself so that the radar will preferentially admit signal power while simultaneously rejecting clutter power.

The Radar Division has an active and ongoing STAP applied research program. Previous work has included the modeling and simulation of shipboard and airborne STAP applications. Areas of current research include using STAP to enhance the detectability of slow moving ground targets, using STAP to improve target location accuracy, and modifying STAP to take into account non-Gaussian interference. The figure above illustrates how STAP is able to pick out a weak target signal obscured by clutter. The left hand panel shows simulated input data, prior to STAP processing, consisting of a ftarget signal at 150 Hz plus clutter. The right hand panel shows those same data after STAP processing.

For further information, email: contact@radar.nrl.navy.mil.