I obtained actual data from a researcher, consisting of a matrix composed of several received signals from an up-ramp fm-cw radar.

Wouldn't be reasonable to plot the spectrogram of a ramp up and obtain a chirp like this ? (This is from MATLAB spectrogram examples)

enter image description here

Instead what I get is this (I know the plots are rotated):

enter image description here

I have read that the received signal if you send a triangular wave, should be a the same but delayed and shifted in frequency.

What do you think?

  • 1
    $\begingroup$ Add more detail to your problem. How did you obtain the received signal ? Also, the frequencies of 0 to 500 Hz are unlikely, are they excursions around an unspecified carrier frequency ? Otherwise, yes, you should theoretically obtained a time-shifted chirp (time shift represents distance to target) and frequency-shifted (freq. shifted represents speed of target) $\endgroup$ – MaximGi Jul 7 '18 at 9:55
  • $\begingroup$ Well, I obtained them from a dataset given me by a researcher and the ramps were already separated. The first Image is just an example obtained from matlab website to explain what I would expect from the results so I don't know about the frequencies. $\endgroup$ – Francesco Pegoraro Jul 7 '18 at 10:17
  • $\begingroup$ well, ask your researcher what you've actually got; we can only guess. My guess is that you've received the beat frequency signal, not the baseband-converted RF signal, and in that case, everything's fine. $\endgroup$ – Marcus Müller Jul 7 '18 at 11:23
  • $\begingroup$ What's the beat frequency signal? Is it the difference between sent and received spectrogram? $\endgroup$ – Francesco Pegoraro Jul 7 '18 at 12:22
  • $\begingroup$ @FrancescoPegoraro it's the signal after downmixing with the TX LO. You should probably brush up your basic knowledge of how classical FMCW radars work if this is news to you! $\endgroup$ – Marcus Müller Jul 8 '18 at 5:09

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