function [] = Orthogonal_sampling()%%%%%%%%%%%%  正交采樣程序  %%%%%%%%%%%%%%%%%%%%%%%% 2007-11-29 %%%%%%%%%%%%close allclear allf0=4200;  %載波頻率fs=4*f0; T= 0.5;    t=-T/2:1/fs:T/2; A  = t+1;     K = 400;             theta =K*pi*t.^2;   xr = A.*cos(2*pi*f0*t+theta);xc = A.*exp(j*theta); figure(1)subplot(2,1,1);plot(t,abs(xc));xlabel('時(shí)間(s)');ylabel('幅度');title('原始實(shí)信號理論復(fù)包絡(luò)幅度')subplot(2,1,2);plot(t,mod(angle(xc)*180/pi,360));xlabel('時(shí)間(s)');ylabel('幅度');title('原始實(shí)信號理論復(fù)包絡(luò)相位')figure(2);F = -fs*floor(length(xr)/2)/length(xr):fs/(length(xr)):fs*floor(length(xr)/2)/length(xr);fft_xr = 20*log10(abs(fft(xr)));fft_xr = fft_xr(2:length(xr)/2+1);fft_xr = [fliplr(fft_xr) fft_xr(1) fft_xr];subplot(2,1,1);plot(t,xr);xlabel('時(shí)間(s)');ylabel('幅度');title('原始信號Xr時(shí)域波形')subplot(2,1,2);plot(F,fft_xr);xlabel('頻率(Hz)');ylabel('幅度(dB)');title('原始信號xr頻譜');%%%%%%%%%  30階FIR濾波器  %%%%%%%%%%%%n=30; f1=1/fs/fs; f2=f0/3;Wn=[f1 f2]/(fs/2);[fir1_b,fir1_a]=fir1(n,Wn);figure(3);freqz(fir1_b,fir1_a);xc_a = 2*xr.*cos(2*pi*f0*t);  xc_a = filter(fir1_b,fir1_a,xc_a);xc_b = 2*xr.*sin(2*pi*f0*t);  xc_b = filter(fir1_b,fir1_a,xc_b);Fs =2*K;   xc_a = xc_a(1:fs/Fs:length(xc_a));  %  同相分量采樣xc_b = xc_b(1:fs/Fs:length(xc_b));  %  正交分量采樣xc_out = xc_a+j*xc_b;A_out = abs(xc_out);      theta_out = mod(angle(xc_out)*180/pi,360);t_out = -length(A_out)/Fs/2+1/Fs:1/Fs:length(A_out)/Fs/2;figure(4)subplot(2,1,1);plot(t_out,A_out);xlabel('時(shí)間(s)');ylabel('幅度');title('解調(diào)得到的信號復(fù)包絡(luò)幅度');axis([-0.25,0.25,0,1.5]);subplot(2,1,2);plot(t_out,theta_out);xlabel('時(shí)間(s)');ylabel('幅度');title(' 解調(diào)得到的信號復(fù)包絡(luò)相位');axis([-0.25,0.25,0,400]);