Passive ISAR part I: framework and considerations

In part I of a two-part passive imaging series, a comprehensive framework for imaging of air targets with passive radar (PR) systems is developed. All operations necessary to convert raw sample data into two-dimensional imagery are touched on. The bistatic geometries, relatively narrow signal bandwidths, and low centre frequencies of most PR illuminators are considered along with their impact on image formation procedures. The core PR processing stages stemming from the illuminators' waveform properties are also examined within this context. The various stages of translational motion compensation are shown to have significant impact on image quality, while target tracking data aids estimation of the apparent target rotation. In turn, this enables cross-range scaling for more advanced methods of image formation to a known image formation plane. Thus, the established framework establishes necessary operations for extension to the multistatic imaging case. The framework is validated in simulation with parameters in accordance with digital television broadcast signals.