Optimal beamforming for range-doppler ambiguity suppression in squinted SAR systems

This paper proposes a method to optimize the beamforming of a planar array in order to maximize the signal to ambiguity ratio, for a general squinted SAR observation geometry. The presence of the receiver thermal noise has been taken into account in the optimization procedure in order to maximize the signal to the overall disturbance ratio. The method works in the joint range-Doppler domain and it provides considerable performance advantages with respect to the uniform weighting case. Most important, the optimization widens the range of Pulse Repetition Frequency (PRF) values that give rise to signal to disturbance ratio values above a desired threshold. This relaxes the choice of the PRF and enables the possibility to widen the swath. The solution is shown to be the generalized eigenvector associated to a pair of matrices depending on the observation geometry, on the Earth reflectivity model and on the PRF. This characteristic allows the fast and reliable computation of the optimal weighting vector and makes the method suitable to be tailored with respect to the specific scope of the mission, i.e. for land, sea or ice exploration, just incorporating the desired predicted (or inferred from previous observation) reflectivity model within the optimization procedure.