Multi-platform ISAR for flying formation

In this paper we exploit a formation of two radar sensors carried by two air platforms to increase the cross-range resolution of ISAR imaging. This is particularly challenging when the motion of the target is limited, as for ISAR images of ship targets from helicopters when the sea state is low. A distributed ISAR technique is devised to process coherently the echoes received by the two radar systems appropriately separated in angle; if both of them are active sensors, one is assumed able to receive and separate the echoes both from its own transmission and from the transmission of the other sensor (MIMO distributed ISAR), otherwise a configuration with one active radar system and one receiving only device is considered (bistatic distributed ISAR). The distributed ISAR technique is tested on simulated data to evaluate its effectiveness in achieving an improvement of the cross-range resolution; for a given number of flying platforms better values of cross-range resolution are obtained when more than one receiving channel per sensor is considered. Specifically, with two platforms, an increase in resolution up to three times the single sensor ISAR case is demonstrated in the MIMO configuration, as opposed to the enhancement of a factor up to two achieved in the bistatic case. Moreover, results obtained by processing the experimental data collected by a ground based radar operating together with a rotating platform are shown to prove the effectiveness of the proposed technique.