I have to Model a chirp signal that was return from a Distance D from target and then multiply with the reference transmitted signal. Which will give me beat frequency signal and then fft to get the range. For this I was searching around and find a pulse LFM SAR implementation.
Nf=2^10; %number of points for freq. range fc=242.4*1E6; %stopfreq B=133.5*1E6; %bandwidth freq=linspace(fc-B,fc,Nf); function [resp] = my_sinthSISO_planresp( pos,freq,tar,tar_amp ) %MY_SINTHSISO_PLANRESP calculates synthetic SISO at position pos response %in frequency range freq on target tar(target postion), tar_amp: RCS like. %Targets and Array must be in the same (image) plane, which XY-coordinate %are represented as complex values. if nargin < 4, tar_amp=ones(size(tar)); end % tar_amp = 1 if not given %speed of light co=299792458; %redistribution of input data tar_dim=numel(tar); tar=reshape(tar,[1,1,tar_dim]); tar_amp=reshape(tar_amp,[1,1,tar_dim]); freq_dim=numel(freq); freq=reshape(freq,[1,freq_dim,1]); pos_dim=numel(pos); pos=reshape(pos,[pos_dim,1,1]); %% algo %targets-elements radial-distances matrix D=abs(repmat(tar,[pos_dim,1,1])-repmat(pos,[1,1,tar_dim])); D=repmat(D,[1,freq_dim,1]); %wavenumber k=2*pi*repmat(freq,[pos_dim,1,tar_dim])/co; %target amplitude tar_amp=repmat(tar_amp,[pos_dim,freq_dim,1]); %SISO response resp=tar_amp.*exp(-1j*k*2.*D); resp=sum(resp,3); end
Question 1: Is resp in a frequency domain? since its dependent on k and k is frequency related. Question 2: if its freq domain then why the inverse fft does not give the desired chirp signal. while its showing: Question 3: If it doesnot represent chirp in frequency domain. Then what it represents?
Question 4: How can I use this data set to model FMCW. Which means multiplication of the chirp at reference and after shift?
I know its quite alot and very basics but I got confused. Thanks.