采用二阶Keystone变换的机动目标ISAR成像算法

针对具有复杂运动的机动目标在相干成像时间内产生的一阶距离徙动和二阶距离徙动的问题，本文提出了基于二阶keystone变换的二维ISAR成像算法。文章首先结合去调频接收机技术，建立并分析了机动目标的回波信号模型，并对回波信号使用二阶keystone变换以去除二阶距离徙动。然后，采用分数阶傅里叶变换（FrFT）估计二阶keystone变换后新生成的二次相位项的调频斜率，并依此补偿该二次相位项。对补偿后的回波信号再次使用二阶keystone变换去除一阶距离徙动。最后，对回波信号使用2D FFT获取机动目标的高分辨2D ISAR图像。数值仿真和实测数据成像结果验证了本算法的有效性。 

ISAR Imaging Algorithm of Maneuvering Targets Using the Second-Order Keystone Transform

In response to the problem that a maneuvering target with complex motions could cause the first order range migration and the second range migration within a coherent processing interval, a 2D ISAR imaging algorithm using the second-order keystone transform in this paper. First, the echo signal model of a maneuvering target is build up and analyzed according to the dechirp-on-receive technique, and the second order keystone transform is used to remove the second-order range migration. Then, the FrFT is used to estimate the chirp rate of the newly resulting quadratic phase term, and the estimated chirp rate is utilized to compensate for the quadratic phase term. The second-order keystone transform is again applied to the compensated echo signal to remove the first-order range migration. Finally, applying 2D FFT to the compensated echo signal to obtain a high-resolution 2D ISAR image. The numerical simulation and real data are conducted to verify the validity of the proposed imaging algorithm.