LFM_radar_radar_LFM加窗_lfm_雷达信号仿真、时域加窗、脉冲压缩_

%%demo of LFM pulse radar %================================================================== function LFM_radar(T,B,Rmin,Rmax,R,RCS) if nargin==0 T=66.6e-6; %pulse duration 66.66us B=200e6; %chirp frequency modulation bandwidth 30MHz Rmin=3e8*T/2; Rmax=50000; %range bin R1=10500; R2=15000; R3=20000; R4=25008; R5=39000; end %================================================================== %%Parameter C=3e8; %propagation speed K=B/T; %chirp slope Rwid=Rmax-Rmin; %receive window in meter 接收窗口，AD采样 Twid=2*Rwid/C; %receive window in second 接收窗口时间 Fs=2*B; Ts=1/Fs; %sampling frequency and sampling spacing Nwid=ceil(Twid/Ts); %接收窗口采样次数， 返回大于或者等于指定表达式的最小整数 %================================================================== %%Gnerate the echo t=linspace(2*Rmin/C,2*Rmax/C,Nwid); %10km:66.6us 50km:333us 一个脉冲周期时间,基于发射脉冲0时刻而言，但取值范围为最近目标时间至最远距离目标时间 td1=t-2*R1/C; %距离为R的目标回波时间 td2=t-2*R2/C; %距离为R的目标回波时间 td3=t-2*R3/C; %距离为R的目标回波时间 td4=t-2*R4/C; %距离为R的目标回波时间 td5=t-2*R5/C; %距离为R的目标回波时间 Srt1=exp(j*pi*K*td1.^2).*(abs(td1)<T/2); Srt2=exp(j*pi*K*td2.^2).*(abs(td2)<T/2); Srt3=exp(j*pi*K*td3.^2).*(abs(td3)<T/2); Srt4=exp(j*pi*K*td4.^2).*(abs(td4)<T/2); Srt5=exp(j*pi*K*td5.^2).*(abs(td5)<T/2); Srt=Srt1+Srt2+Srt3+Srt4+Srt5; %=======================加窗处理=========================================== win_hann = hann(length(t)); win_rec= rectwin(length(t)) %矩形窗函数 win_bar = bartlett(length(t))%三角窗 % win_han = hanning(length(t1)) %汉宁窗 win_ham = hamming(length(t)) %汉明窗 win_bm = blackman(length(t))%blackman窗 Srt_hann= Srt.*win_hann'; Srt_rec= Srt.*win_rec'; Srt_bar= Srt.*win_bar'; Srt_ham= Srt.*win_ham'; Srt_bm= Srt.*win_bm'; figure; t1=linspace(0,262143,262144); plot(t,win_hann,'-r',t,win_rec,'-g',t,win_bar,'-b',t,win_ham,'-c',t,win_bm,'-y'); legend('hann','rec','bar','ham','bm'); title('不同窗函数时域波形'); %================================================================== %%匹配滤波器 Nfft=2^nextpow2(Nwid+Nwid-1); %number needed to compute linear Srw_hann=fft(Srt_hann,Nfft); %fft of radar echo 返回 Nfft 点 DFT Srw_rec=fft(Srt_rec,Nfft); Srw_bar=fft(Srt_bar,Nfft); Srw_ham=fft(Srt_ham,Nfft); Srw_bm=fft(Srt_bm,Nfft); Nchirp=ceil(T/Ts); %pulse duration in number t0=linspace(-T/2,T/2,Nchirp); St=exp(j*pi*K*t0.^2); %chirp signal Sw=fft(St,Nfft); %fft of chirp signal figure; subplot(2,1,1) plot(t0*1e6,real(St));axis tight; xlabel('Time in u sec');ylabel('Amplitude') title('发射基带信号'); subplot(2,1,2) freq=linspace(-Fs/1,Fs/1,Nchirp); plot(freq*1e-6,fftshift(abs(fft(St))));%fftshift的操作是将fft结果以fs/2为中心左右互换 title('基带信号幅度频谱'); xlabel('Frequent in Mhz'); grid on;axis tight; % Sot_hann=fftshift(ifft(Srw_hann.*conj(Sw))); %signal after pulse compression conj返回Sw共轭复数 Sot_rec=fftshift(ifft(Srw_rec.*conj(Sw))); %signal after pulse compression conj返回Sw共轭复数 Sot_bar=fftshift(ifft(Srw_bar.*conj(Sw))); %signal after pulse compression conj返回Sw共轭复数 Sot_ham=fftshift(ifft(Srw_ham.*conj(Sw))); %signal after pulse compression conj返回Sw共轭复数 Sot_bm=fftshift(ifft(Srw_bm.*conj(Sw))); %signal after pulse compression conj返回Sw共轭复数 % figure % subplot(211) % t1=linspace(0,262143,262144); % plot(t1,abs(Sot1));axis tight; % title('匹配滤波时域信号'); % subplot(212) % plot(t1,abs(Sot));axis tight; % title('匹配滤波频域信号'); %======================================================== N0=Nfft/2-Nchirp/2; Z_hann=abs(Sot_hann(N0:N0+Nwid-1)); Z_hann=Z_hann/max(Z_hann); Z_hann=20*log10(Z_hann+1e-6); Z_rec=abs(Sot_rec(N0:N0+Nwid-1)); Z_rec=Z_rec/max(Z_rec); Z_rec=20*log10(Z_rec+1e-6); Z_bar=abs(Sot_bar(N0:N0+Nwid-1)); Z_bar=Z_bar/max(Z_bar); Z_bar=20*log10(Z_bar+1e-6); Z_ham=abs(Sot_ham(N0:N0+Nwid-1)); Z_ham=Z_ham/max(Z_ham); Z_ham=20*log10(Z_ham+1e-6); Z_bm=abs(Sot_bm(N0:N0+Nwid-1)); Z_bm=Z_bm/max(Z_bm); Z_bm=20*log10(Z_bm+1e-6); figure subplot(311) plot(t*1e6,Srt_rec);axis tight; xlabel('Time in u sec');ylabel('Amplitude') title('Radar echo with rectangle window but without compression'); subplot(312) plot(t*C/2,Z_rec) axis([0,50000,-80,0]); xlabel('Range in meters');ylabel('Amplitude in dB') title('Radar echo with rectangle window and compression'); subplot(313) plot(t*C/2,Z_bm) axis([0,50000,-80,0]); xlabel('Range in meters');ylabel('Amplitude in dB') title('Radar echo with black window and compression'); %以矩形窗为参考，同一个窗口对比不同窗 figure; plot(t*C/2,Z_hann,'-r',t*C/2,Z_rec,'-g',t*C/2,Z_bar,'-b',t*C/2,Z_ham,'-c',t*C/2,Z_bm,'-y'); axis([14000,16000,-120,0]); xlabel('Range in meters');ylabel('Amplitude in dB') title('同一目标使用不同窗函数截断和脉压波形'); legend('hann','rec','bar','ham','bm'); %==================================================================