Range-dependence compensation for bistatic STAP using focusing matrices

We consider the problem of developing a linear transformation process to compensate for range-dependent bistatic clutter spectral dispersion. Clutter non-homogeneity is problematic in space-time adaptive processing (STAP) for airborne bistatic radar systems. The non-homogeneity is due to variation in angle-Doppler response at different bistatic ranges. In typical STAP applications this leads to poor clutter covariance matrix estimates and therefore reduced clutter cancellation. Previous approaches to compensating for this effect seek to modify the secondary data in order to align the clutter statistics for each bistatic range cell. Linear transformation approaches such as Doppler warping and angle-Doppler compensation determine the necessary shift in angle and Doppler between range cells at the spectral center of the clutter ridge but result in incomplete registration of the data. The registration-based compensation approach matches multiple points along the clutter ridge but is a nonlinear method that forms an estimate covariance matrix without an explicit linear transformation of the data. We propose instead a registration-based compensation method which aligns multiple registration points using focusing matrices to accomplish the linear transformation of the data.