%this function is to produce LFM signal
%fs is the sampling frequency,fi is the intermediate frequency,b is bandwidth,T is pulse width.
%tn1 is the cutpoint of T by 1/fs,tn2 is the total length of tn1(the total numbers of cutpoints).
%tn3 is a sequence from 1 to tn2,tn4 is the observing point.
%signal is the LFM signal that we get.
function [signal,tn1,tn2,tn3,tn4]=produce(fs,fi,b,T)
k=b/T;
N=1024;
tn1=-T/2:1/fs:(T/2-1/fs);
tn2=length(tn1);
tn3=1:tn2;
tn4=(tn3/tn2)*T*1e+6;
signal=cos(2*pi*(fi*tn1+k*tn1.*tn1/2));