Multisubband-GRFT-Based Space Target Imaging Algorithm With Low SNR in Stepped Frequency Carrier LFM Radar

To achieve high-resolution imaging of distant space targets, a stepped frequency carrier linear frequency modulation (SFCLFM) radar can be used for prolonged observation. In such circumstances, the target's motion is intricate, the signal-to-noise ratio (SNR) of the echoes is low, and subband phase errors are present. This complexity renders traditional imaging methods susceptible to failure. Therefore, an imaging algorithm of the space target based on multiple subbands' generalized radon Fourier transform (MS-GRFT) is proposed. Initially, the signal echo from the space target in the SFCLFM radar is modeled, incorporating subband phase errors and noise into the model. Subsequently, motion parameter coarse estimation is achieved using the GRFT of individual subband data, compensating for translational components using peak values in the parameter domain. Simultaneously, the parameter range of the actual target motion is also obtained. Next, utilizing parallel GRFT to obtain parameter estimation results for each subband data, detecting partial motion parameters using constant false alarm ratio (CFAR) technology after noncoherent accumulation across multiple subbands. Sharpness is employed as the objective function to estimate subband phase errors, and analytical solutions are then derived. Subsequently, error compensation is applied to the GRFT results of multiple subbands, and wideband synthesis is performed in the parameter domain. Finally, CFAR is employed for parameter detection, and point-wise motion compensation (MOCO) is applied to achieve high-resolution range-instantaneous-Doppler (RID) images of space targets. Computer simulations and real experimental results validate the effectiveness of the proposed algorithm.