problems with chirp LFM impulse in radar

Hi to everyone,:
how can I extract Doppler information from a chirp impulse LFM like
cos(2*pigreco*f0*t+k*pigreco*t^2) ?;
At receiver I have cos(2*pigreco*f0*(t-2R/c)+k*pigreco*(t-2R/c)^2),
multipling by cos(2pigrecof0t) and low pass filtering I obtain
cos(-2*pigreco*f0*2R/c+k*pigreco*(t-2R/c)^2).
I would like to get this term apart from others: cos(-2*pigreco*f0*2R/c) to
work it on.
Thank you very much to everyone who want to help me


davide

Hi David
May be I don't understand your question properly

I think you are trying to get the doppler from a single chirp pulse ?

from my limited knowledge i don't think you can get the doppler info
from a single pulse.

 radar usally transmit a number of pulses, on the returned pulses we
take the FFT on range wise.

from which we can easily measure the doppler of the target.


regards
bijoy

"Davide" <dgramugTIDIMEZZO@tin.it> wrote in message news:<Vi9Lc.23550$OR2.1182651@news3.tin.it>...
> Hi to everyone,:
> how can I extract Doppler information from a chirp impulse LFM like
> cos(2*pigreco*f0*t+k*pigreco*t^2) ?;
> At receiver I have cos(2*pigreco*f0*(t-2R/c)+k*pigreco*(t-2R/c)^2),
> multipling by cos(2pigrecof0t) and low pass filtering I obtain
> cos(-2*pigreco*f0*2R/c+k*pigreco*(t-2R/c)^2).
> I would like to get this term apart from others: cos(-2*pigreco*f0*2R/c) to
> work it on.
> Thank you very much to everyone who want to help me
> 
> 
> davide

pbijoy@rediffmail.com (bijoy) wrote in message news:<261d3065.0407290444.72663df8@posting.google.com>...
> Hi David
> May be I don't understand your question properly
> 
> I think you are trying to get the doppler from a single chirp pulse ?
> 
> from my limited knowledge i don't think you can get the doppler info
> from a single pulse.
> 
>  radar usally transmit a number of pulses, on the returned pulses we
> take the FFT on range wise.
> 
> from which we can easily measure the doppler of the target.
> 
> 
> regards
> bijoy
> 
> "Davide" <dgramugTIDIMEZZO@tin.it> wrote in message news:<Vi9Lc.23550$OR2.1182651@news3.tin.it>...
> > Hi to everyone,:
> > how can I extract Doppler information from a chirp impulse LFM like
> > cos(2*pigreco*f0*t+k*pigreco*t^2) ?;
> > At receiver I have cos(2*pigreco*f0*(t-2R/c)+k*pigreco*(t-2R/c)^2),
> > multipling by cos(2pigrecof0t) and low pass filtering I obtain
> > cos(-2*pigreco*f0*2R/c+k*pigreco*(t-2R/c)^2).
> > I would like to get this term apart from others: cos(-2*pigreco*f0*2R/c) to
> > work it on.
> > Thank you very much to everyone who want to help me
> > 
> > 
> > davide

The problem isn't the single pulse, it's the pulse type. The chirp
pulse is doppler insensitive. To extract doppler information you could
use a bank of matched filters, each replica corresponding to a
different doppler value. Unfortunately these will be pretty widely
spaced apart because of the doppler insensitivity. You should look at
an ambiguity diagram for you pulse. Normally replicas are placed at
the 3dB points.

If you used a CW pulse the doppler information is detected by the
frequency shift, and the bank of matched filters conveniently turns
into a FFT filter bank.

Cheers,
David