New inverse algorithm for focused radar image reconstruction of a rotating object

A new inverse algorithm using the proposed method to obtain two‐dimensional (2‐D) high‐resolution inverse synthetic aperture radar (ISAR) images of rotating targets is described. Generally, to obtain images using ISAR, the reflected signals of an object are measured at a uniform frequency interval and rotation angle interval. If a 2‐D fast Fourier transform (FFT) is performed using the measured data, an unfocused image might be obtained. To obtain a focused image using a 2‐D FFT, the measured signal is resampled by interpolating the known samples disposed on a polar raster to obtain new samples disposed on a rectangular raster. To improve resolution and reduce computation time, an alternative to the resampling process is proposed in this paper. This proposed sampling method directly measures samples on a rectangular raster, thus avoiding the interpolation process at the cost of increased complexity in the sampling scheme. In this case it is assumed that rotation angle of object and step frequency can be controlled. In this paper, three types of image reconstruction methods are presented, and images obtained through simulation and experiment are compared. The methods are the unfocused imaging method, the focused imaging method with interpolation, and the focused imaging method with proposed scheme.