线性调频信号脉冲压缩-数字下变频程序 DDC

线性调频信号脉冲压缩-数字下变频程序DDC

clc;

clear all;

close all;

B=5e6; %%信号带宽

f0=30e6; %中频

fs=40e6; %采样频率

fs1=(20/3)*1e6; %%抽取后频率

T=24.9e-6; %%时宽

k=B/T;

fk=127; %%做DDC时的低通滤波器的阶数

fid=fopen('20090724fc1yindao4-0.dat','r');

sss=fread(fid,32*4096,'int16');

fclose(fid);

figure(100);plot(sss);grid on;xlabel('点数');ylabel('幅度');title('32个周期信号时域波形');grid on;

L=length(sss);

N=4096;

R=fix(L/N);

for r=1:R

ss(r,:)=sss((r-1)*N+1:1:r*N);

end

figure(1);plot(ss(R,:));xlabel('点数');ylabel('幅度');title('信号时域波形');grid on;

%%%%%%%%%%%%%%% 低通滤波器%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

ff=[0 1/8 1/4 1];

aa=[1 1 0 0];

b=firpm(fk,ff,aa);

[h,w]=freqz(b,1,1024);

% figure(2);

% f=linspace(0,fs/2,1024);

% plot(f/1e6,20*log10(abs(h)));xlabel('f/Mhz');ylabel('dB');title('低通滤波器的幅频响应');grid on;

%%%%%%%%%%%%%%%

DDC %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

ddcs=zeros(R,N+fk);

for r=1:1:R

n=-N/2:1:N/2-1;

si=ss(r,:).*cos(2*pi*f0*n/fs);

sq=-ss(r,:).*sin(2*pi*f0*n/fs);

I=conv(si,b);

Q=conv(sq,b);

ddcs(r,:)=I+j*Q;

end

m=1:N+fk;

figure(3);

subplot(211);plot(m,I);xlabel('点数');ylabel('幅度');title('DDC后I路信号波形');

subplot(212);plot(m,Q);xlabel('点数');ylabel('幅度');title('DDC后Q路信号波形');

% figure(4);

% subplot(211);plot(m,abs(ddcs(R,:)));xlabel('点数');ylabel('幅度');title('DDC后信号时域波形');grid on;

% sf=fftshift(fft(ddcs(R,:),2048));

% f=linspace(0,fs,2048);

% subplot(212);plot(f/1e6,abs(sf));xlabel('MHz');ylabel('幅度');title('DDC后信号频谱');grid on;

%%%%%%%%%%%%%%%%%%% 6倍抽取%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%

PD=fix((N+fk)/6);

cddcs=zeros(R,PD);

for r=1:R

dd=ddcs(r,:);

for pd=1:PD

dd1(pd)=dd(6*pd);

end

cddcs(r,:)=dd1;

end

%%%抽取之后信号的加窗脉压%%%%%%%%%%%%%%%%%%%%%%%

N1=T*fs;

t=linspace(-T/2,T/2,N1);

hs=exp(j*k*pi*t.^2);%%%用于未抽取信号

ha=conj(fliplr(hs));

P=fix(N1/6);

for p=1:P

hb(p)=ha(6*p); %%%%%%%%%%对匹配滤波器进行抽取

end

window=hamming(P); %%%%%%%加hamming窗

chmyw=zeros(R,PD+P-1);

h=hb.*window.';

for r=1:R

chmyw(r,:)=conv(cddcs(r,:),h);

end

figure(6);

plot(20*log10(abs(chmyw(R,:))/max(abs(chmyw(R,:)))));xlabel('点数');ylabel('dB');title('抽取之后信号加窗脉压');grid on;

figure(7);

plot((abs(chmyw(R,:))));xlabel('点数');ylabel('幅度');title('抽取之后信号加窗脉压');grid on;