线性调频脉压仿真

Posted 2021-07-07 fpga&matlab

       雷达是Radar（RAdio Detection And Ranging）的音译词，意为“无线电检测和测距”，即利用无线电波来检测目标并测定目标的位置，这也是雷达设备在最初阶段的功能。典型的雷达系统如图1.1，它主要由发射机，天线，接收机，数据处理，定时控制，显示等设备组成。利用雷达可以获知目标的有无，目标斜距，目标角位置，目标相对速度等。现代高分辨雷达扩展了原始雷达概念，使它具有对运动目标(飞机，导弹等)和区域目标(地面等)成像和识别的能力。雷达的应用越来越广泛。

  

雷达发射机的任务是产生符合要求的雷达波形（Radar Waveform），然后经馈线和收发开关由发射天线辐射出去，遇到目标后，电磁波一部分反射，经接收天线和收发开关由接收机接收，对雷达回波信号做适当的处理就可以获知目标的相关信息。

%%demo of chirp signal

T=10e-6;                          %pulse duration10us

B=30e6;                           %chirp frequency modulation bandwidth 30MHz

K=B/T;                            %chirp slope

Fs=2*B;Ts=1/Fs;                   %sampling frequency and sample spacing

N=T/Ts;

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

St=exp(j*pi*K*t.^2);                 %generate chirp signal

subplot(211)

plot(t*1e6,real(St));

xlabel('Time in u sec');

title('Real part of chirp signal');

grid on;axis tight;

subplot(212)

freq=linspace(-Fs/2,Fs/2,N);

plot(freq*1e-6,fftshift(abs(fft(St))));

xlabel('Frequency in MHz');

title('Magnitude spectrum of chirp signal');

grid on;axis tight;

%%demo of chirp signal after matched filter

T=10e-6;                            %pulse duration10us

B=30e6;                             %chirp frequency modulation bandwidth 30MHz

K=B/T;                              %chirp slope

Fs=10*B;Ts=1/Fs;                    %sampling frequency and sample spacing

N=T/Ts;

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

St=exp(j*pi*K*t.^2);                   %chirp signal

Ht=exp(-j*pi*K*t.^2);                  %matched filter

Sot=conv(St,Ht);                      %chirp signal after matched filter

subplot(211)

L=2*N-1;

t1=linspace(-T,T,L);

Z=abs(Sot);Z=Z/max(Z);                %normalize

Z=20*log10(Z+1e-6);

Z1=abs(sinc(B.*t1));                   %sinc function

Z1=20*log10(Z1+1e-6);

t1=t1*B;                                        

plot(t1,Z,t1,Z1,'r.');

axis([-15,15,-50,inf]);grid on;

legend('emulational','sinc');

xlabel('Time in sec \\times\\itB');

ylabel('Amplitude,dB');

title('Chirp signal after matched filter');

subplot(212)                          %zoom

N0=3*Fs/B;

t2=-N0*Ts:Ts:N0*Ts;

t2=B*t2;

plot(t2,Z(N-N0:N+N0),t2,Z1(N-N0:N+N0),'r.');

axis([-inf,inf,-50,inf]);grid on;

set(gca,'Ytick',[-13.4,-4,0],'Xtick',[-3,-2,-1,-0.5,0,0.5,1,2,3]);

xlabel('Time in sec \\times\\itB');

ylabel('Amplitude,dB');

title('Chirp signal after matched filter (Zoom)');

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