Abstract: For the sampling bandwidth to be reduced, ISAR echoes are often dechirped at the receiver with the reference ranges varying according to the target position each pulse. Thus, the echoes are non-coherent after dechirping. A remedial method is presented by the following two steps: Firstly we control the dechirp reference ranges approximately by hardware; secondly we compensate the Doppler phase error caused by the reference signals delay error precisely through the comparison between reference signals and benchmark signal. As a result, a group of sampled target echoes can be made coherent without phase autofocusing operation. This method will improve the ISAR imaging speed greatly and be of special value in ISAR imaging when the signal to noise ratio becomes low.

Key words: ISAR imaging, dechirp, coherence, reference range, delay control