About Doppler FFT of FMCW radar

[shoko_s]

Hello, 

I have some question about Doppler FFT(2D FFT) of FMCW radar. 

I understand that Doppler FFT of FMCW radar is achieved by the following steps. 

Step 1) Do FFT on ADC data in each chirp. (RangeFFT) → Get range 

Step 2) Do FFT on the RangeFFT result for each frame. (DopplerFFT) → Get velocity 

https://par.nsf.gov/servlets/purl/10074169 

If the target is always moving equidistant from the radar, can FMCW radar detect velocity? 

I think that Doppler radar cannot detect velocity in this case, because there is no frequency shift due to the Doppler effect. 

Please advise. 

Regards, Shoko 

[Deepa_V · Accepted solution]

Hi @shoko_s ,

FMCW radar uses a Multi-chirp configuration for Doppler Estimation which in-turn uses the dependency on phase (not essentially on the frequency shift) to evaluate the velocity of moving object. 

In essence, the phase change of the targets moving equidistant from Radar be distinguished provided they are moving with different velocities. 

For further information, you can also refer the sections:  'How can we measure speed with multi chirp FMCW?', 'How is the data processed in a multi chirp FMCW?' and 'How can the angle be estimated?' in the document : https://www.infineon.com/dgdl/Infineon-Radar%20FAQ-PI-v02_00-EN.pdf?fileId=5546d46266f85d6301671c76d... .

Hope this helps !

Best regards,

Deepa

[shoko_s]

Hello Deepa, 

Thank you for the detailed response. 

I understand your explanation. 

Thank you, Shoko