Bistatic spotlight synthetic aperture radar (SAR) which uses a separated transmitter and receiver has been studied intensively due to its flexibility. To reconstruct the image for the bistatic SAR in the parallel track configuration, where the transmitter and the receiver have equal velocity, we modify the omega-k algorithm. Specifically, using the extended Taylor approximation (ETA), we convert the parallel track configuration into the single track configuration. Then, using the principle of the stationary phase, we propose an analytical method to increase the image quality of bistatic SAR systems.