Long-baseline 3D interferometric ISAR

In recent years, interferometric inverse synthetic aperture radar (InISAR) systems with three radar receivers have been developed to achieve full three-dimensional reconstructions of targets. One fundamental limitation of such systems is the potential for phase ambiguities to arise from the distance between the receivers, or baselines. This paper presents an extension to 3D InISAR systems that calls for two additional radar receivers, thus forming a slightly larger radar system than previously studied. The additional measurements at the new receivers allow phase ambiguities to be resolved beyond the limits imposed by the traditional setup, thus effectively enlarging the aperture of the radar. This results in two important theoretical advantages: (i) it is more robust against measurement noise and is thus capable of more accurate imaging of targets, and (ii) it is possible to image larger targets. Both of these advantages will benefit the 3D InISAR's role in applications such as automatic target recognition. The problem of phase ambiguity resolution is posed as an equivalent problem in number theory, for which a solution is readily available. The improvements to imaging performance are demonstrated using numerical simulations.