Abstract: A new algorithm is proposed for radar echo cancelling based on the group delay of the LFM (Linear Frequency Modulated) signal. Firstly, the received signal is multiplied by the conjugation of its delayed version to get the frequency difference between them. The received signal’s frequency is then shifted using the frequency difference. According to the target’s RCS(Radar Cross Section), phase and amplitude modulation are made in order to get the signal having the same frequency as the echo pulse but with the opposite phase. This signal cancels the radar echo signals. One of the jammer structures which can realize the algorithm is given and the method for reducing nonlinear phase errors is presented. Theoretical analysis and simulation show that the novel algorithm effectively reduces the signal power received by the radar receiver even when the chirp rate is unknown.The algorithm is also workable when the jammer has a large time delay.

Key words: radar countermeasures, jamming, cancelling, linear frequency modulated, active stealth