clear all;
clc;
close all;
f0=20e6;%模拟信号中频
f1=10e6;%数字本振频率
fs=40e6;%采样频率
Ts=1/fs;%采样周期
Treceive=200e-6;%脉冲重复频率
Tp=40e-6;%脉冲宽度
BW=2e6;%中频信号带宽
K=BW/Tp;%带宽时宽比5.11E10
N=fs*Treceive;%脉冲重复频率内的采样次数8000次
N1=fs*Tp;%脉冲宽度内的采样次数1600次
%-------generate input lfm signal---------%
t=-Tp/2:Tp/N1:Tp/2-Tp/N1;
%length(t)=1600
xs=cos(2*pi*(f0*t+0.5*K*t.^2)); %LFM信号表达式
fid = fopen('G:\project\xs.txt','w');
if (fid==-1)
disp('Couldn''t open file filsim.vec for writing');
end
x=round(xs*(2^13-1)); %length(x)=1600
fprintf(fid,'%d \n',x);
f=0:fs/N1:fs-fs/N1;
%length(f)=1600
%f5=0:fs/N1:fs
%length(f5)=1601
figure(1);
fly=fft(x); % length(fly)=1600
lfm_f=20*log10(abs(fly));%length(lfm_f)=1600
%lfm_f=real(fly);
plot(f,lfm_f);
hold;
f2=-fs:fs/N1:-fs/N1; % length(f2)=1600
plot(f2,lfm_f);
grid;
title ('输入LFM信号频谱图');
xlabel('Frequency(Hz)');
ylabel('Magnitude(dB)');
%------------generate NCO cos---------%
t1=0:Ts:(N1-1)*Ts;
nco1=cos(2*pi*f1*t1);
%------------generate NCO sin---------%
nco2=-sin(2*pi*f1*t1);
% nco1=round(nco1*(2^17-1));
% nco2=round(nco2*(2^17-1));
%数字本振的频谱图
nco=nco1+j*nco2;
nco_fft=fft(nco);
f=0:fs/N1:fs-fs/N1;
figure(2);
plot(f,20*log10(abs(nco_fft)));