Analysis and Focusing for Bistatic Forward-looking Sar in Spaceborne/stationary Configuration

The conventional monostatic SAR shows a limitation of achieving a high azimuth (angular) resolution if a forward-looking geometry is used [1]-[2]. One problem of the forward-looking configuration is that the differences in the Doppler frequencies of adjacent terrain points in the along-track direction are much smaller than the differences in the Doppler frequencies of adjacent terrain points in the across-track direction [2]-[4]. Another one is the left/right ambiguity which is introduced by the fact that the targets located at symmetrically about the flight path of the receiver have the same range history. Therefore, the monostatic SAR reaches its limits if a twodimensional resolution is desired for the forward-looking case [5]. However, in some applications, a forwardlooking imaging radar is highly desirable, e.g. military and aircraft landing systems. Fortunately, the bistatic configuration in principle offers the possibility of the forward-looking image [6]-[8]. In this paper, a Bistatic Forward-Looking SAR (BFLSAR) model will be considered, and the imaging geometry is shown in Fig. 1 (The platform with the forward-looking beam can be stationary.). In this model, the transmitter works in the conventional side-looking case, while the separated receiver operates in the forward-looking mode. In this configuration, the differences in the Doppler frequencies of adjacent terrain points in the along-track direction are enlarged by the contribution of the transmitter. Therefore, the high azimuth resolution can be achieved. However, the forward-looking configuration of the receiver will also introduce two problems. One is the significant range-azimuth coupling. Another is still the left/right ambiguity of the slant range of receiver (i.e. range cell migration ambiguity).