% function LFM_disp
close all;clear; clc
c = 3*1e8; %%光速 m/s
Bw = 5*1e6; %%雷达波形 信号带宽
Tau = 50*1e-6; %%雷达波形 脉冲宽度
f0 = 10*1e9; %%载波频率
deta_t = 1/(Bw*16); %%保证采样率
time = 0:deta_t:Tau;
N_t = length(time);
time = (0:1:(N_t -1))*deta_t ;%%重新调整一下时间采样序列
range = c*time/2; %%距离采样序列
range_cell = mean(diff(range));
f0 = -Bw/2;gamma = Bw/Tau
%%原始信号
x = exp(i*2*pi*(f0*time+1/2*gamma*time.^2));
x_fft = ifftshift( fft(x)) ;f = linspace(-1/2*1/deta_t, 1/2*1/deta_t,N_t);
x_fft_amp = 20*log10(abs(x_fft));x_fft_amp_max = max(x_fft_amp ); x_fft_amp = x_fft_amp - x_fft_amp_max ;
figure; subplot(2,1,1);plot(range , real(x),'k');hold on; plot(range, imag(x),'r-.');xlabel('range / m')
legend('I', 'Q');xlabel('range /m');title('before range compress');
subplot(2,1,2);plot(f/1e6,x_fft_amp );xlabel('freq / MHz');ylim([-15,5]);title('bandwidth disp')
%%脉冲压缩 (FFT 实现)
P = nextpow2(2*N_t);
x_append = [x, zeros(1,2^P - N_t)]; fft_x_append = fft(x_append);
x_match_append = [conj(fliplr(x)),zeros(1,2^P-N_t)]; fft_x_match_append = fft(x_match_append );
fft_x_pc = fft_x_append .*fft_x_match_append;
x_pc = ifft(fft_x_pc);
range_pc = (0:1:2^P-1) *range_cell;
figure;plot(range_pc,abs(x_pc));xlabel('range /m');title('after range compress')
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