Preprocessing by eigenbeams and Doppler filters to improve performance of detection of signal number

In this paper, a preprocessing by spatial eigenbeamforming and coherent Doppler filtering for improving detection performance of signal number for highly-correlated signals in low SNR condition is proposed for radar system with digital beamformer. The proposed method utilizes that all of highly-correlated target signals exist in one specific Doppler bin with different Doppler frequency. In this method, eigenbeams from target covariance matrix are formed followed by coherent Doppler filtering with DFT for SNR improvement prior to signal number detection such as MDL. Evaluation of proposed preprocessing with MDL by computer simulation showed higher performance compared with conventional MDL. Quantitatively required SNR is reduced by approximately 7 dB compared with conventional MDL when 50% of probability of correct signal number detection is specified for two closely-spaced targets scenario.