clear;
clc
close all
c=3e8; % 光速
Te=100e-6; % 时间???????????
Be=1e6; %?带宽???
mu=Be/Te;
Ts=1/(2*Be);
Ro=70e3;
fo=c/0.03;
Vr=688;
t=0:Ts:Te-Ts;
W=exp(j*pi*mu*t.^2);
Wf=fft(W,1024);
nnn=fix((Ro-30e3)/75);
R=0:75:15e3-75;
for i=1:200
for k=1 :64
Ri(k,i)=R(i)-Vr*Ts*(k-1);
end
end
taoi=2*Ri/c;
echo=10^0.225*0.707*(randn(64,1024)+j*randn(64,1024));
j=sqrt(-1);
for i=1:64
echo(i,nnn:nnn+199)=echo(i,nnn:nnn+199)+...
exp(-j*2*pi*fo*taoi(i,:)+j*pi*mu*taoi(i,:).^2);
end
for i=1:64
sp2(i,:)=ifft(fft(echo(i,:),1024).*conj(Wf),1024);
end
for k=1:1024
sct(:,k)=abs(fftshift(fft(sp2(:,k),256)));
end
sct=sct./max(max(sct));
sp=sp2./max(max(sp2));
figure(1)
plot(20*log10(abs(sp')))
ylabel('-db')
title('回波信号')
axis([1 1024 -30 0])
figure
plot(20*log10(sct'))
ylabel(' - db')
title('回波信号FFT')
axis([1 1024 -30 0])
r=((1:1024)*75+30e3)./1e3;
dp=(-128:127)*(Be/128)/1e3;
figure
mesh(r,dp,sct)
xlabel('距离/km')
ylabel('多普勒频率/kHz')
title('三维傅里叶变换')
figure
contour(r,dp,sct)
axis([30 100 -200 200])
xlabel('距离/km')
ylabel('多普勒频率/kHz')
title('R-fd关系')
grid on
dp=(-32:31)*(Be/32)/1e3;
figure
mesh(r,dp,abs(echo)/max(max(abs(echo))))
xlabel('距离/km')
ylabel('多普勒频率/kHz')
title('回波信号')
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