信号与系统实验四

10.1利用fourier函数求下列信号的傅里叶变换F(jw),并用ezplot函数绘出其幅度频谱|F(jw)|和相位频谱)(。观察比较三个信号的幅频特性和相频特性，并用傅里叶的性质加以解释。symstphaseimref=sin(2*pi*t)/(2*pi*t);F=fourier(f);subplot(3,1,1)ezplot(f);title('原图')axis([-pipi-0.31.1])subplot(3,1,2)ezplot(abs(F))title('幅度谱')axis([-3*pi3*pi0.30.6])im=imag(F);re=real(F);phase=atan(im/re);subplot(3,1,3)ezplot(phase)title('相位谱')axis([-3*pi3*pi-0.50.5])10.2试用ifourier函数求下列傅里叶变换的逆变换，并画出其时域波形。symstwF=2*pi*cos(w/2)/(pi^2-w^2);f=ifourier(F,t)ezplot(f);axis([-0.80.8-0.21.1]);title('时域波形')10.3symstwf1=sym('Heaviside(t+1)-Heaviside(t-1)')subplot(2,2,1)ezplot(f1)holdonaxis([-2201.1]);plot([-1-1],[01])holdonplot([11],[01])holdontitle('f1(t)')Fw=fourier(f1,t,w)FFw=maple('convert',Fw,'piecewise');FFP=abs(FFw)subplot(2,2,2)ezplot(FFP,[-10*pi10*pi]);axis([-10*pi10*pi02.1])title('F(jw)')f=Fw*Fw;subplot(2,2,3)ezplot(f)title('f(t)=f1(t)*f1(t)')subplot(2,2,4)ezplot(abs(f),[-10*pi10*pi])axis([-3*pi3*pi05])title('F(jw)')10.4b=[002];a=[0.040.42];[h,w]=freqs(b,a,100);h1=abs(h);h2=angle(h);subplot(2,1,1);plot(w,h1);holdonplot([7.07117.0711],[00.707],':');plot([07.0711],[0.7070.707],':');axis([05001.5]);grid;title('H(j\omega)d幅频特性');subplot(2,1,2);plot(w,h2*180/pi);axis([0100-2000]);gridtitle('H(j\omega)相频特性');