Range Doppler and image autofocusing for FMCW Inverse Synthetic Aperture Radar

Inverse Synthetic Aperture Radar (ISAR) is a well known technique for obtaining high resolution radar images. ISAR techniques have been succesfully applied in the recent past in combination with pulsed coherent radar. In order to be more appealing to both civilian and military fields, imaging sensors are required to be low-cost, low-powered and compact. Coherent pulsed radars do not account for these requirements as much as FMCW radars. However, FMCW radars transmit a LMF sweep in a relatively long time interval. During such an interval the assumption of stop&go is no longer valid, that is the target cannot be considered stationary during the acquisition of the entire sweep echo. Therefore, the target motion within the sweep must be taken into account. Such a problem, which has been considered and solved for SAR systems, is reformulated and solved for ISAR systems, where the target cooperation is removed and additional unknowns are added to the signal model. Specifically, in the present work, the authors define a complete FMCW-ISAR received signal model, propose an ISAR image formation technique suitable for FMCW radar and derive the Point Spread Function (PSF) of the imaging system.