clear, hold off format compact J = sqrt(-1); close all% Get root file name for saving resultsfile=input('Enter root file name for data and listing files: ','s');

% form radar chirp pulseT = 10e-6; % pulse length, seconds W = 10e6; % chirp bandwidth, Hz fs = 12e6; % chirp sampling rate, Hz; oversample by a littlefprintf('\nPulse length = %g microseconds\n',T/1e-6) fprintf('Chirp bandwidth = %g Mhz\n',W/1e6) fprintf('Sampling rate = %g Msamples/sec\n',fs/1e6) s = git_chirp(T,W,fs/W); % 120-by-1 array plot((1e6/fs)*(0:length(s)-1),[real(s) imag(s)]) title('Real and Imaginary Parts of Chirp Pulse') xlabel('time (usec)') ylabel('amplitude') gridNp = 20; % 20 pulses jkl = 0:(Np-1); % pulse index array, 慢时间采样的序列，注意第一个PRI标记为0是为了慢时间起始时刻从零开始 PRF = 10.0e3; % PRF in Hz PRI = (1/PRF); % PRI in sec T_0 = PRI*jkl; % relative start times of pulses, in sec g = ones(1,Np); % gains of pulses T_out = [12 40]*1e-6; % start and end times of range window in sec， 这个就是接收窗的时间宽度Trec T_ref = 0; % system reference time in usec， T_ref = 0指T_0=0时，r_at_T_0 = ri ；当T_0 ~= 0时，r_at_T_0 = ri - vi*T_0(j)fc = 10e9; % RF frequency in Hz; 10 GHz is X-bandfprintf('\nWe are simulating %g pulses at an RF of %g GHz',Np,fc/1e9) fprintf('\nand a PRF of %g kHz, giving a PRI of %g usec.',PRF/1e3,PRI/1e-6) fprintf('\nThe range window limits are %g to %g usec.\n', ... T_out(1)/1e-6,T_out(2)/1e-6)% Compute unambiguous Doppler interval in m/sec % Compute unambiguous range interval in metersvua = 3e8*PRF/(2*fc); %第一盲速 rmin = 3e8*T_out(1)/2; rmax = 3e8*T_out(2)/2; rua = 3e8/2/PRF;fprintf('\nThe unambiguous velocity interval is %g m/s.',vua) fprintf('\nThe range window starts at %g km.',rmin/1e3) fprintf('\nThe range window ends at %g km.',rmax/1e3) fprintf('\nThe unambiguous range interval is %g km.\n\n',rua/1e3)% Define number of targets, then range, SNR, and % radial velocity of each. The SNR will be the actual SNR of the target in % the final data; it will not be altered by relative range.Ntargets = 4; del_R = (3e8/2)*( 1/fs )/1e3; % in km ranges = [2 3.8 4.4 4.4]*1e3; % in km SNR = [-3 5 10 7]; % dB vels = [-0.4 -0.2 0.2 0.4]*vua; % in m/sec% From SNR, we compute relative RCS using the idea that SNR is proportional % to RCS/R^4. Students will be asked to deduce relative RCS. rel_RCS = (10.^(SNR/10)).*(ranges.^4); rel_RCS = db(rel_RCS/max(rel_RCS),'power')

fprintf('\nThere are %g targets with the following parameters:',Ntargets) for i = 1:Ntargets fprintf('\n range=%5.2g km, SNR=%7.3g dB, rel_RCS=%7.3g dB, vel=%9.4g m/s', ... ranges(i)/1e3,SNR(i),rel_RCS(i),vels(i) ) end% Now form the range bin - pulse number data mapdisp(' ') disp(' ') disp('... forming signal component') y = radar(s,fs,T_0,g,T_out,T_ref,fc,ranges,SNR,vels); % y是337-by-20的矩阵% add thermal noise with unit powerdisp('... adding noise') %randn('seed',77348911); [My,Ny] = size(y); nzz = (1/sqrt(2))*(randn(My,Ny) + J*randn(My,Ny)); % 产生方差为1的复高斯白噪声 y = y + nzz;% create log-normal (ground) "clutter" with specified C/N and 具体原理不清楚，需要时套用此格式即可！ % log-normal standard deviation for amplitude, uniform phase % Clutter is uncorrelated in range, fully correlated in pulse #disp('... creating clutter') CN = 20; % clutter-to-noise ratio in first bin (dB) SDxdB = 3; % in dB (this is NOT the sigma of the complete clutter) ncc=10 .^((SDxdB*randn(My,Ny))/10); ncc = ncc.*exp( J*2*pi*rand(My,Ny) );% Force the power spectrum shape to be Gaussiandisp('... correlating and adding clutter') G = exp(-(0:4)'.^2/1.0); G = [G;zeros(Ny-2*length(G)+1,1);G(length(G):-1:2)];for i=1:My ncc(i,:)=ifft(G'.*fft(ncc(i,:))); end

% rescale clutter to have desired C/N ratio pcc = var(ncc(:)); ncc = sqrt((10^(CN/10))/pcc)*ncc; % 10*log10(var(ncc(:))/var(nzz(:))) % check actual C/N% Now weight the clutter power in range for assume R^2 (beam-limited) loss cweight = T_out(1)*((T_out(1) + (0:My-1)'*(1/fs)).^(-1)); cweight = cweight*ones(1,Np); ncc = ncc.*cweight; % var(ncc)可以看出20列clutter的方差均在30左右y = y + ncc;[My,Ny]=size(y); d=(3e8/2)*((0:My-1)*(1/fs) + T_out(1))/1e3; % T_out(1))/1e3是接收窗的起始时刻 plot(d,db(y,'voltage')) xlabel('distance (km)') ylabel('amplitude (dB)') grid% Save the data matrix in specified file. % Save the student version in the mystery file. % Also save all parameter value displays in corresponding filedata_file=[file,'.mat']; mystery_file=[file,'_mys.mat']; listing_file=[file,'.lis'];eval(['save ',data_file,' J T W fs s Np PRF PRI T_out fc vua', ... ' rmin rmax rua Ntargets ranges vels SNR rel_RCS y']);eval(['save -v6 ',mystery_file,' J T W fs s Np PRF T_out fc y']);fid=fopen(listing_file,'w');fprintf(fid,['\rDESCRIPTION OF DATA IN FILE ',file,'.mat AND ',file,'_mys.mat\r\r']); fprintf(fid,'\rPulse length = %g microseconds\r',T/1e-6); fprintf(fid,'Chirp bandwidth = %g Mhz\r',W/1e6); fprintf(fid,'Sampling rate = %g Msamples/sec\r',fs/1e6); fprintf(fid,'\rWe are simulating %g pulses at an RF of %g GHz',Np,fc/1e9); fprintf(fid,'\rand a PRF of %g kHz, giving a PRI of %g usec.',PRF/1e3,PRI/1e-6); fprintf(fid,'\rThe range window limits are %g to %g usec.\r', ... T_out(1)/1e-6,T_out(2)/1e-6); fprintf(fid,'\rThe unambiguous velocity interval is %g m/s.',vua); fprintf(fid,'\rThe range window starts at %g km.',rmin/1e3); fprintf(fid,'\rThe range window ends at %g km.',rmax/1e3); fprintf(fid,'\rThe unambiguous range interval is %g km.\r\r',rua/1e3); fprintf(fid,'\rThere are %g targets with the following parameters:', ... Ntargets); for i = 1:Ntargets fprintf(fid,'\r range=%5.2g km, SNR=%7.3g dB, rel_RCS=%7.3g dB, vel=%9.4g m/s', ... ranges(i)/1e3,SNR(i),rel_RCS(i),vels(i) ); endfclose(fid);fprintf(['\n\nData is in file ',data_file]) fprintf(['\nStudent data is in file ',mystery_file]) fprintf(['\nListing is in file ',listing_file,'\n\n']) _________________________________________________________________________用到的函数function y = radar( x, fs, T_0, g, T_out, T_ref, fc, r, snr, v ) % RADAR simulate radar returns from a single pulse or burst % of identical pulses % usage: % R = radar( X, Fs, T_0, G, T_out, T_ref, Fc, R, SNR, V ) % X: baseband single pulse waveform (complex vector) % Fs: sampling frequency of input pulse [in Hz] % T_0: start time(s) of input pulse(s) [sec]