Design of LFM cancelling system based on group delay

This paper presents an active stealth system for the linear frequency modulation (LFM) signal which based on the group delay of it. The cancelling system structure is given and the conditions that can be generated for cancelling the radar echo are presented. By making the LFM signal and its delayed signal multiplication to obtained the frequency difference between them. And then frequency shift the LFM signal using the difference. Finally, according to the target's RCS database by amplitude and phase modulation to get the cancelling signal which having the same frequency as the echo pulse but with the opposite phase. Theoretical analysis and simulation show that the system can workable when the phase error and the time delay is relatively large.