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

The University of Nebraska-Lincoln has developed an ultrawideband random no ise radar operating over the 1- to 2-GHz frequency range. The system uses t he technique of heterodyne correlation, and is thus phase coherent. It has therefore been used in applications such as interferometry, polarimetry, an d Doppler estimation. This assesses the performance of this radar as a rang e-Doppler imaging system, in particular, inverse synthetic aperture radar ( ISAR). By performing turntable experiments, we examine a number of issues t hat arise both from the wideband nature of the radar system and from the ra ndomness of the transmit signal. Although the ultrawideband nature of the s ignal does yield some ambiguity as to the cross-range resolution of the sys tem, it is seen that one may use the usual equation for cross-range resolut ion in narrowband systems with reasonable confidence. In addition, the rand om nature of the transmit waveform gives rise to variations from look to lo ok in the ISAR images. High correlations are obtained for voltage and power amplitudes, while the complex voltage and the phase angle show low correla tions 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. (C) 2001 Society of Ph oto-Optical Instrumentation Engineers.