Variable Velocity Ambiguity Numbers Compensation Method for Near Space Target Detection

Near space target is of high velocity and high acceleration, which will result in the velocity ambiguity, range migration (RM), and Doppler frequency migration (DFM). To achieve good performance of coherent integration, the velocity ambiguity, RM and DFM should be mitigated. Due to the high acceleration of the target, the velocity ambiguity numbers may vary in the coherent integration time, which leads to the decrease of the signal-to-noise ratio (SNR). A variable velocity ambiguity numbers compensation method is proposed in this paper. The signal is divided into two segments according to the position where the velocity ambiguity number changes, which is obtained by searching. To correct the RM and DFM, the second-order Keystone transform (SKT) and the fractional Fourier transform (FRFT) are combined. The initial phases of the two segments are different. Therefore, the initial range and velocity of the second segment are compensated based on the target parameters. The proposed method solves the problem of variable velocity ambiguity numbers in the coherent integration time, which improves the performance of target detection. Finally, the effectiveness of the proposed method is verified through simulation results.