maiya.m

说明多普勒频率对脉冲压缩输出的影响

clear all;
close all;
clc;
%产生信号
fc=10e6;
bw=2e6;
fs=40e6;
tao=10e-6;
t=0:1/fs:tao-1/fs;
N=length(t);
f=0:fs/N:fs/2-fs/N;
k=bw/tao;
y=cos(2*pi*fc*t+pi*k*t.^2);
y_fft=fft(y);
figure
subplot(211)
plot(t*1e6,y)
subplot(212)
plot(f*1e-6,abs(y_fft(1:length(y_fft)/2)))
%正交解调
n=0:N-1;
local_i=2*cos(2*pi*fc/fs*n);
local_q=2*sin(2*pi*fc/fs*n);
fbb_i=y.*local_i;
fbb_q=y.*local_q;
window=hamming(67);
b=fir1(66,0.5,window);
fbb_i=[fbb_i,zeros(1,33)];
fbb_q=[fbb_q,zeros(1,33)];
fbb_i=filter(b,1,fbb_i);
fbb_q=filter(b,1,fbb_q);
fbb_i=fbb_i(34:end);
fbb_q=fbb_q(34:end);
figure
subplot(211)
plot(t,fbb_i)
subplot(212)
plot(t,fbb_q)

fbb=fbb_i+j*fbb_q;
fbb_fft=fft(fbb);
figure
plot(f,abs(fbb_fft(1:length(fbb_fft)/2)))
%产生理想线性调频脉冲压缩系数
M=4096;
D=bw*tao;
match_filter=2*sqrt(D)/(fs*tao)*fliplr(conj(fbb));
match_filter_fft=fft(match_filter,M);
%产生理想回波信号
delay=90e-6;
num=round(delay*fs);
tao1=100e-6;
t1=0:1/fs:tao1-1/fs;
signal=[zeros(1,num),y];
signal_fft=fft(signal);
figure
subplot(211)
plot(t1*1e6,signal)
subplot(212)
plot(abs(signal_fft(1:length(signal_fft)/2)))
local_i=2*cos(2*pi*fc*t1);
local_q=2*sin(2*pi*fc*t1);
fbb_i=signal.*local_i;
fbb_q=signal.*local_q;
window=hamming(67);
b=fir1(66,0.5,window);
fbb_i=[fbb_i,zeros(1,33)];
fbb_q=[fbb_q,zeros(1,33)];
fbb_i=filter(b,1,fbb_i);
fbb_q=filter(b,1,fbb_q);
fbb_i=fbb_i(34:end);
fbb_q=fbb_q(34:end);
signal=fbb_i+j*fbb_q;
%脉冲压缩处理
signal_fft=fft(signal,M);
pc_result_fft=signal_fft.*match_filter_fft;
pc_result=ifft(pc_result_fft,M);
figure
subplot(211)
plot(t1,signal)
subplot(212)
plot(t1,abs(pc_result(1:length(signal))))
% plot((0:1/fs:length(pc_result)/fs-1/fs),abs(pc_result))