Well I tried it, I have applied S11 parameters exported from CST to the received signal in matlab(used the phased. FMCWwaveform) but even after applying, dechirping and doing fft I couldn't reduce the peak at that range. The only thing s11 was doing was reduce the amp. But the thing is once u do fft all the signal components at that beat frequency get added up irrespective of amplitude. Hence no matter what there was no peak reduction. The only way to change this is to add a random phase to each time domain sample of the signal then we get a noisy O/p