Rejection of Doppler shifted multipaths in airborne passive radar

In this article, we consider the problem of rejecting multipath ground echoes in airborne passive radar. In such an application, these multipath echoes present some Doppler-shift due to the movement of the airborne platform. Classic rejection methods with rejection mask sampled at the cell resolution in delay and Doppler lead to strong sidelobe residue that tend to mask the target responses. We propose here first to oversample this mask, solving the projection problem induced using the Moore-Penrose pseudo-inverse. This solution however requires the knowledge of the right oversampling factor necessary to get good rejection performance. We thus propose a different approach that permits to perform rejection over a continuous set, thus insuring good rejection. This solution provides some insight on the dimensionality of the subspace spanned by this continuous set, which can in turn be used to properly choose the oversampling factor. Simulations are provided for rejection on a Doppler interval, and in the context of airborne passive radar dealing with range and Doppler.