NonuniformlyRotating Ship Refocusing in SAR Imagery Based on the Bilinear Extended Fractional Fourier Transform Nonuniformlyrotating ship refocusing is very significant in the marine surveillance of satellite synthetic aperture radar (SAR). The majority of ship imaging algorithms is based on the inverse SAR (ISAR) technique. On the basis of the ISAR technique, several parameter estimation algorithms were proposed for nonuniformly rotating ships. But these algorithms still have problems on crossterms and noise suppression. In this paper, a refocusing algorithm for nonuniformly rotating ships based on the bilinear extended fractional Fourier transform (BEFRFT) is proposed. The ship signal in a range bin can be modeled as a multicomponent cubic phase signal (CPS) after motion compensation. BEFRFT is a bilinear extension of fractional Fourier transform (FRFT), which can estimate the chirp rates and quadratic chirp rates of CPSs. Furthermore, BEFRFT has excellent performances on crossterms and noise suppression. The results of simulated data and Gaofen3 data verify the effectiveness of BEFRFT.

Range and Velocity Estimation for DFRFTOFDMBased Joint Communication and Sensing Systems As being able to share radio frequency (RF) hardwares and spectrum bandwidth, joint communication and radar sensing system has attracted a lot of attention. The integrated waveforms based on orthogonal frequencydivision multiplexing (OFDM) with fast Fourier transform (FFTOFDM) and OFDM with discrete fractional Fourier transform (DFRFTOFDM) have been developed. However, the existing derived ambiguity function does not distinguish the two waveforms clearly. In addition, few range and velocity estimation algorithm for DFRFTOFDMbased integrated waveform has been investigated. Therefore, in this paper we derive the ambiguity function of the DFRFT OFDMbased waveform based on wideband analysis, which shows the superiority of the DFRFTOFDMbased integrated waveform on range resolution. Moreover, range and velocity estimation algorithms based on pulse compression and coherent accumulation are proposed for the DFRFTOFDMbased integrated waveform, respectively. Simulation results validate that the proposed algorithms can accurately estimate the distances and velocities of multiple moving targets.