SAR image formation for forward-looking radar receivers in bistatic geometry by airborne illumination

The capabilities in imaging for forward-looking radar receivers are severely limited so far. This application gap is especially valid for monostatic radars due to their problem producing a significant Doppler shift orthogonal to the direction of illumination. So a two-dimensional resolution of an area of investigation is nearly unattainable. Here bistatic configurations with separated receiver and transmitter offer a new potential to circumvent this difficulty. In this paper selected results of a performed airborne field campaign from November 2006 are presented in which a forward-looking radar receiver was brought into action. Thereby a SAR system operated as a moving illuminator emitting chirped millimeter wave signals. After introducing the bistatic geometry and the used radar parameters the capability of the approach is shown in detail by the evaluation of one processed SAR image. Herein occurring reflections can be associated clearly to the illuminated scenery due to the achieved resolution in azimuth. Finally the effect of shadowing and the related geometrical behavior are outlined.