雷达成像的RD算法

clear all;
%%%(I) parameters' definition
c=3e+8; % speed of light
pi=3.1415926; % pi
j00=sqrt(-1); % square root of -1
res_a=1; % required azimuth resolution
res_r=1; % required range resolution
k_a=1.2; % azimuth factor
k_r=1.2; % range factor
Ra=4000.; % radar working distance 雷达工作距离
va=70.; % radar/platform forward velocity
Tp=1.e-6; % transmitted pulse width
fc=1.e+9; % carrier frequency
FsFactor = 1.0;
lamda=c/fc; % wavelength
B=k_r*c/2./res_r; % required transmitted bandwidth
Fs=B*FsFactor; % A/D sampling rate
bin_r=c/2./Fs % range bin
gama=B/Tp; % range chirp rate
delta_theta=k_a*lamda/2/res_a; % required azimuth opening angle
% corresponding to processed bandwith
% (should be less than azimuth 3dB opening angle)
La=Ra*delta_theta; % required synthetic aperture
Ta=La/va; % required synthetic aperture time
thetas_c=pi/2; % zero squint
fdc=2*va*cos(thetas_c)/lamda; % doppler centriod
fdr=-2*va*va*sin(thetas_c)^2/lamda/Ra; % doppler rate
Bd=abs(fdr)*Ta; % doppler bandwidth
prf=100.; % PRF
%%%(II) echo return modelling(point target)
na=fix(Ta*prf/2); % azimuth sampling number
ta=-na:na;
ta=ta/prf; % slow time along azimuth
xa=va*ta; % azimuth location along flight track
na=2*fix(na);
%x0=[0 0 0 0 0 0 -60 -30 30 60];
%R0=[-10 0 10 20 30 40 0 0 0 0];
x0=[0 ];
R0=[0 ];
Npt_num = length(x0);
% single point target's azimuth location
% positive towards forward velocity
% single point target's slant range location
ra=zeros(Npt_num, length(xa)); % positive towards far range
for i=1:Npt_num
ra(i,:)=sqrt((Ra+R0(i)).^2+(xa+x0(i)).^2); % single point target's slant range history
end
rmax=max(max(ra)); % max. slant range
rmin=min(min(ra)); % min. slant range
rmc=fix((rmax-rmin)/bin_r); % range migration
rg=0*ra;
rg=fix((ra-rmin)/bin_r+1); % range gate beause of range migration
rgmax=max(max(rg));
rgmin=min(min(rg));
nr=round(Tp*Fs); % min range samples
tr=1:fix(nr)+1;
tr=tr/Fs-Tp/2; % fast time along range

[m,Na]=size(ta);
Nr=nr+rgmax;
Na
Nr
sig=zeros(Na,Nr);
for i=1:Na
for k=1:Npt_num
sig(i,rg(k,i):rg(k,i)+nr)=sig(i,rg(k,i):rg(k,i)+nr)+exp(-j00*4*pi/lamda*ra(k,i))*exp(-j00*pi*gama*(tr).^2);
end
end
disp('end of echo return modelling')
%figure
%contour(abs(sig))

%%%===============================================================================
for i=1:Na
sig(i,:)=fftshift(fft(sig(i,:)));
end
disp('end of range fft')
dfr=Fs/Nr;
fr=((0:Nr-1)-Nr/2)*dfr;
phase1=exp(-j00*pi*(fr).^2/gama);
for i=1:Na
sig(i,:)=ifft(fftshift( s

ig(i,:).*phase1) );
end
disp('end of range compression')
figure
contour(abs(sig))
figure
imshow(abs(sig))
for i=1:Nr
sig(:,i)=fftshift(fft(sig(:,i)));
end
disp('end of azimuth fft')
fdr=-2*va*va/lamda/Ra;
dfa=prf/Na;
fa=((0:Na-1)-Na/2)*dfa;
figure
%contour(abs(sig(Na,:)))
plot(abs(sig(Na,:)))
R=4;
Up00=zeros(size(1:Nr*R+2000));
kkk=1:Nr;
for i=1:Na
Up00=0*Up00;
Up00(1:Nr*R)=interp(sig(i,:),R);
dRa=Ra/sqrt(1-(lamda*fa(i)/2/va)^2)-Ra;
kpos(i)=round(R*dRa/bin_r);
sig(i,:)=Up00((kkk-1)*R+kpos(i)+1);
end
%figure
%contour(abs(sig))
figure
%contour(abs(sig(Na,:)))
plot(abs(Up00))

disp('Range motion correction')
rr=rmin+((1:Nr)-1)*bin_r;
delt_beta = sqrt(1-(lamda/2/va*fa).^2)-1;
phase2 = exp((j00*4*pi/lamda)*(delt_beta'*rr));
sig = sig.*phase2;
for i=1:Nr
sig(:,i)=ifft(sig(:,i));
end
figure
contour(abs(sig));