Bistatic forward-looking SAR (BF.SAR) has many potential applications, such as self-landing in bad weather and military detection. Therefore, BFSAR receives considerable attention recently. The imaging algorithms for BFSAR are the difficulties of the study. The original Loffeld's Bistatic Formula (LBF) can handle most general bistatic SAR configurations well. But in some complex bistatic geometries, such as high squint or forward-looking cases, the performance of LBF is degenerated. Some extended LBF (ELBF) methods have been developed, which improve the performance of LBF in some special geometries, but still not the forward-looking configuration. In this paper, we modify the LBF method and try to solve the instantaneous azimuth frequencies of transmitter and receiver directly. Then, we can obtain a bistatic point target reference spectrum (BPTRS), which is accurate enough for forward-looking configuration. A range Doppler algorithm (RDA) based on this BPTRS is derived. Finally, simulations validate the accuracy of the modified Loffeld's Bistatic Formula (MLBF) and effectiveness of imaging algorithm.
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