Inverse synthetic aperture radar imaging using a coherent ultrawideband random noise radar system

The University of Nebraska-Lincoln has developed an ultrawideband random noise radar operating over the 1- to 2-GHz frequency range. The system uses the technique of heterodyne correlation, and is thus phase coherent. It has therefore been used in applications such as interferometry, polarimetry, and Doppler estimation. This assesses the performance of this radar as a range-Doppler imaging system, in particular, inverse synthetic aperture radar (ISAR). By performing turntable experiments, we examine a number of issues that arise both from the wideband nature of the radar system and from the randomness of the transmit signal. Although the ultrawideband nature of the signal does yield some ambiguity as to the cross-range resolution of the system, it is seen that one may use the usual equation for cross-range resolution in narrowband systems with reasonable confidence. In addition, the random nature of the transmit waveform gives rise to variations from look to look in the ISAR images. High correlations are obtained for voltage and power amplitudes, while the complex voltage and the phase angle show low correlations from look to look. Finally, we present polarimetric color images of a complex target that captures its polarimetric scattering characteristics, which may be useful in automatic target recognition.