Multistatic and MIMO ISAR techniques

The exploitation of ISAR data simultaneously acquired by multiple radar systems is considered in this chapter in order to enhance the quality of ISAR images of moving targets with respect to the conventional single-sensor case, thus making ISAR images more effective when used for target classification and recognition. In particular, multi-sensor data are exploited in order to increase the cross-range resolution of ISAR images of rotating targets and to improve the accuracy in the estimation of the target motion. The distributed (multi-sensor) ISAR technique is devised for two different cases: (i) MIMO case with each platform carrying an active radar, that transmits and receives RF waveforms, (ii) multistatic case with a single platform carrying an active radar (transmitting and receiving) and the remaining platforms equipped with passive sensors (namely receiving only). For such distributed imaging system: (a) the PSF is derived showing the capability at providing an increase of the crossrange resolution up to the number of platforms in the multistatic case and even higher in the MIMO case; (b) the required focusing technique is also presented and discussed following a decentralized approach; (c) multi-sensor based target motion estimation techniques are considered showing the performance improvement with respect to the conventional single-sensor case. This distributed ISAR system could be of great benefit in applications where the target rotation angle is insufficient to guarantee the desired resolution. A typical case is the imaging of ship targets with rotation induced by the sea swell structure under low sea state conditions. Results obtained against synthetic ISAR data are presented; moreover, experimental data collected in an anechoic chamber against different targets on a rotating platform are processed by following the presented distributed ISAR technique to validate the approach.