0
$\begingroup$

I'm starting research in radar and compressed sensing, but I’m still building my background in these areas. I’m currently diving into radar, following the book Fundamentals of Radar and Signal Processing by Mark A. Richards.

I don’t have anyone to ask for clarification on some topics, so I have a few questions I’m hoping someone can help with. Any guidance would be greatly appreciated!

Q1. Are unchirping and range compression independent operations, or do they depend on each other? For example, is unchirping used for continuous wave radar, while range compression is specific to pulsed FMCW radar?

Q2. In unchirping, do we transmit a signal, listen for a period of time, record the received samples, and then mix them with the transmitted signal? In this case, should the pulse duration be long enough to ensure some overlap with the maximum designed range?

Q3. I understand that the Doppler effect is typically measured with pulse-to-pulse sampling. However, doesn’t pulse compression disrupt the phase history needed to analyze Doppler shifts?

Q4. If unchirping and range compression are used independently, what are the advantages of using both techniques? Where can I find more detailed resources or papers discussing this?

Apologies for the long post, and thank you in advance for your help! I’m still trying to get my head around some of these concepts, and I really appreciate any insight.

Many thanks!

Improve this question
$\endgroup$
4
  • 1
    $\begingroup$ Envidia gave a good answer. Dechirping is not just an FMCW operation, though. It is quite common SAR systems which are typically pulsed. $\endgroup$
    – Baddioes
    Commented Nov 15 at 19:29
  • $\begingroup$ Interesting. In this case, being the mixing operation equivalent to point wise multiplication, what happens if the reference signal does not overlap with a pulse in the received data ? (sorry i know this is too basic) $\endgroup$
    – confused_echo
    Commented Nov 17 at 17:41
  • $\begingroup$ The reference chirp is relative to scene center at that pulse, so that shouldn’t be an issue if your system parameters are appropriately designed. $\endgroup$
    – Baddioes
    Commented Nov 18 at 0:46
  • $\begingroup$ Thank you very much :) $\endgroup$
    – confused_echo
    Commented Nov 18 at 14:48

1 Answer 1

Reset to default
1
$\begingroup$

I'm going to give some brief answers since you have multiple questions. If you want to dive into either one in detail, you can ask a separate question if an answer doesn't exist on the site already.

Q1. Are unchirping and range compression independent operations, or do they depend on each other? For example, is unchirping used for continuous wave radar, while range compression is specific to pulsed FMCW radar?

De-chirping and range compression are indeed related but they are separate operations. In FMCW, you must de-chirp to yield the beat frequencies, which are then taken through the DFT (range compression) to yield the range profile. You don't de-chirp or range compress in classical CW, but perform a similar mixing process to get beat frequencies for Doppler.

Q2. In unchirping, do we transmit a signal, listen for a period of time, record the received samples, and then mix them with the transmitted signal? In this case, should the pulse duration be long enough to ensure some overlap with the maximum designed range?

Ideally, CW/FMCW allows you to start mixing your transmit signal with the return signal immediately. There is no need to wait for a listen period to start the mixing and sampling process, otherwise you would lose some of the benefits of FMCW in particular. The intention should be to simultaneously transmit the signal, mixing a copy of it with the returns for a period of time (de-chirping), which then go through sampling, and eventually the DFT. Remember that part of the magic of FMCW is the analog mixing process, which reduces the requirements on the ADC.

Regarding the maximum range: yes there is a relationship between what your maximum telemetered range can be and comes from basic radar theory, albeit FMCW has another layer on how to determine that.

Q3. I understand that the Doppler effect is typically measured with pulse-to-pulse sampling. However, doesn’t pulse compression disrupt the phase history needed to analyze Doppler shifts?

It does not. The pulse-to-pulse Doppler phase-shift is maintained through pulse compression.

Q4. If unchirping and range compression are used independently, what are the advantages of using both techniques? Where can I find more detailed resources or papers discussing this?

Again, they can be done independently but unless you're doing some special type of processing, you don't get anything useful unless you do both.

If you're already reading what I think you meant to be the Mark A. Richards book, then all of these questions can be answered there with some study, specifically the first five chapters.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Thank you for taking the time to reply to these questions. I did put the name of the author wrong for some reason.. This helped me alot ! $\endgroup$
    – confused_echo
    Commented Nov 15 at 16:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.