How does this time domain plot refer to the frequency plot in the automotive adapting cruise control example?

Hello, I am studying the example " Automotive Adaptive Cruise Control Using FMCW Technology ", and there is something that does not make too much sense for me. Please help me to clarify it.

In my opinion, the time domain plot presented below does not correspond to the frequency plot stated.

The time domain plot seems to have an increment in the frequency only until the middle of the plot (3,7 micro seconds), which then starts to decrease in frequency again until the end of the sweep. On the other hand, the frequency domain plot shows a sawtooth updown signal, and not a triangular. For this reason, I believe they don't correspond.

Thanks in advance for helping me to clarify it.

Answer 1

[Honglei Chen]

This is because the signal is critically sampled (bandwidth 150 MHz and sampling rate 150 MHz) so visually it looks as if the signal's frequency is decreasing. However what gets plotted is only the real part of the complex signal. Once we put real and imaginary parts of the signal together, then the frequency information can be properly retrieved.

HTH

[Hector Andres Gonzalez Diaz]

Hello, you are correct, I just plotted it for two sweeps with a higher sampling rate and the pattern is evident now. Thank you very much.