Phase Error Calculation Caused by Start-Stop Approximation in Processing FMCW Radar Signals for SAR Imaging

The current synthetic aperture radar (SAR) image formation algorithms have been developed for pulse radar systems, and they are desired for use in for frequency-modulated continuous wave (FMCW) radar systems. Since there is a difference between the outputs of pulse radar and FMCW radar, it is necessary to adapt these algorithms to the output of the pulse radar. In addition, the start-stop approximation, which can be used for the signal processing of pulse radar systems, should be taken into account for FMCW radar systems because the pulse duration of the pulse radar is relatively small in comparison to the modulation time of the FMCW radar. In this study, the phase error caused by the start-stop approximation in processing the data measured by an FMCW radar system for synthetic aperture imaging is investigated. The important results of this study indicate that the start-stop approximation is valid for processing FMCW SAR data in many cases. If the following circumstances occur simultaneously, such as a high radar signal frequency, long modulation time, high platform speed, and short propagation range, then the approximation may become invalid. The simulations and experiments performed with a wideband 154 GHz FMCW radar support this statement.