IMage formation algorithm for bistatic forward-looking SAR

The conventional monostatic SAR shows a limitation of achieving a high azimuth (angular) resolution if a forward-looking geometry is used. Bistatic SAR offers a possibility of the forward-looking formation image, e.g. one platform operates as a separated illuminator while another works in a forward-looking mode. In this special bistatic configuration, the forward-looking beam will introduce two problems. The first one is the significant Doppler shift, which will produce the range-azimuth coupling. The second one is that the targets located at symmetrically about the flight path of the forward-looking platform have the same antenna-to-target range which would cause the range migration ambiguity of the receiver. This paper will develop a mathematical model to describe the Doppler characteristic of bistatic forward-looking SAR (BFLSAR). Based on this model, the previous bistatic point reference spectrum (BPTRS) can be applied. Using the BPTRS, a modified range-Doppler algorithm is proposed to handle the two problems and focus BFLSAR data in the azimuth-invariant configuration. Finally, simulation experiment is used to validate the proposed model and processing approach.