Range Doppler Response has a linear bias

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ramesh on 24 Jul 2014
Edited: Honglei Chen on 28 Jul 2014
The range doppler response of matlab's phased array system toolbox seems to have a linear bias for doppler frequency. The system is a moving radar platform (at certain altitude) and a stationary ground target and ground clutter (modeled as phased.ConstantGammaClutter object). In my particular case, 0 velocity will have everything in correct frequency (0 Hz for ground clutter and target), however for 10 m/s velocity, the frequency is 88 Hz more than what it should be (for both ground clutter and ground target), for 20 m/s it is 88*2 Hz more and so on. I am not sure if I'm missing some parameters, my phased.RangeDopplerResponse object is defined as follows
myResponse = phased.RangeDopplerResponse('RangeMethod','Matched Filter', ...
'PropagationSpeed',c, 'DopplerOutput','speed',...
'SampleRate', fs,'OperatingFrequency',fc,...
'DopplerFFTLengthSource','Property', ...
Also, the limit on doppler frequency is supposed to be -PRF/2 to PRF/2 but it is a bit beyond that. This is not of too much concern, but the bias on doppler frequency is an issue. Any help or clarification is greatly appreciated. thanks

Answers (1)

Honglei Chen
Honglei Chen on 25 Jul 2014
Hi Ramesh,
Is it possible for you to provide a little more details? Like what are the fs and fc? What are the position and velocity of the radar and the target? Otherwise it's hard to guess the issue.
ramesh on 28 Jul 2014
Hi Honglei,
I think I figured out what was happening. It is partly my fault. My PRF was 10 KHz which gives me about 15 km of unambiguous range, my targets were at around 9 km so I didn't need to sample beyond a particular index and my code did exactly that. But when I used matlab's RangeDopplerResponse, I think it assumed that my ranges went from 0 to 15 km which caused my limit on doppler frequency to go beyond prf/2 (in negative and positive side) like I mentioned in my original post. I think that is what caused the doppler frequency to be incorrect. Now that I have removed the max-range limit, the problem is rectified.
I greatly appreciate your help. thank you

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