Subband STAP processing, the fifth generation

Adaptive array processing has moved through several stages of evolution. First there was spatial only adaptation, using gradient based algorithms. Second was true space-time adaptivity using time-taps on multiple channels. Third came more rapid convergence, using sample matrix inversion strategies. Fourth came dimensionally large system solutions, which focused on the need for reduced DOF such as beamspace, eigenspace, MUSIC, ESPRIT, BASS-ALE, etc. This paper argues that we are on the threshold of the fifth generation of STAP; mainly STAB in the subband domain. Subband STAP, is an elegant and computationally efficient solution to the need for increasing bandwidth in radar and sonar processing as well as mobile communications. We begin by motivating the need for wider bandwidths, from a SAR imaging perspective. Next, we show that the computational burden of wideband STAP is untenable for existing and emerging military requirements. Having motivated a compelling need we then propose subband STAP as a solution, motivated from an active sensor perspective. We describe subband STAP as an extension of the familiar STAP 3D datacube (range, angle, Doppler) to a 40 hypercube (subband range, angle, subband Doppler, subband frequency). Subbanding allows us to overcome challenging wideband effects such as Doppler-frequency coupling, high-resolution range migration, target self-nulling, channel decorrelation, and dispersion. We describe the challenges of subband STAP interference rejection and subband recombination with artifacts