信号与系统实验傅里叶变换.docx

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1、信号与系统实验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d（w）。<1>f1(t)=(sin(2*pi*t)/(2*pi*t)2syms t phase im ref=sin(2*pi*t)/(2*pi*t);F=fourier(f);subplot(3,1,1)ezplot(f);title('ԭͼ')axis(-pi pi -0.3 1.1)subplot(3,1,2)ezplot(abs(F)title('·ù

2、¶Èͼ')axis(-3*pi 3*pi 0.3 0.6)im=imag(F); re=real(F); phase=atan(im/re);subplot(3,1,3) ezplot(phase) title('Ïàλͼ') axis(-3*pi 3*pi -0.5 0.5)<2>f2(t)=sin(2*pi*(t-2)/(2*pi*(t-2)syms t phase im ref=sin(2*pi*(t-2)/(2*pi*(t-2);F=fourie

3、r(f);subplot(3,1,1)ezplot(f);title('ԭͼ')axis(-pi 2*pi -0.3 1.1)subplot(3,1,2)ezplot(abs(F)title('·ù¶ÈÆ×')axis(-3*pi 3*pi 0.3 0.6)im=imag(F);re=real(F); phase=atan(im/re);subplot(3,1,3) ezplot(phase) title('ÏàÎ

4、7;Æ×') axis(-3*pi 3*pi -0.5 0.5)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。<1>F(iw)=1/2Sa2(w/4);syms t w F=8*(sin(w/4)2/(w2);f=ifourier(F,t) ezplot(f); axis(-0.8 0.8 -0.2 1.1); title('ʱÓò²¨ÐÎ')输出为：f =-(4*fourier(cos(w/2)/w2, w, -t) + 4*

5、pi*t*(2*heaviside(t) - 1)/(2*pi)报错：Error using inlineeval (line 15)Error in inline expression => -(4.*fourier(cos(w./2)./w.2, w, -t) + 4.*pi.*t.*(2.*heaviside(t) -1)./(2.*pi) Undefined function 'fourier' for input arguments of type 'double'.Error in inline/feval (line 34) INLINE_O

6、UT_ = inlineeval(INLINE_INPUTS_, INLINE_OBJ_.inputExpr, INLINE_OBJ_.expr);Error in ezplotfeval (line 54) z = feval(f,x(1),y(1);Error in ezplot>ezimplicit (line 258) u = ezplotfeval(f, X, Y);Error in ezplot (line 154) hp = ezimplicit(cax, f1, vars, labels, args:);Error in sym/ezplot (line 61) h =

7、ezplot(fhandle(f);Error in Untitled (line 4)ezplot(f);调试过很多次了，仍然出不来图像。10.3 已知信号f（t）的波形如图所示，使用MATLAB傅里叶变换数值算法，解决一以下问题：<1>求f1(t)的傅里叶变换F1(jw)，并绘制出其幅度频谱|F1（jw）|以及相位频谱曲线。<2>求f2(t)=f(t-2)的傅里叶变换F2(jw)|，并绘制出其幅度频谱|F2（jw）|以及相位频谱曲线。观察分析傅里叶变换的时移特性。（1）dt=0.005;t=-2:dt:2;f=(t/2+1/2).*(t>=-1)&(t

8、<=1);N=2000;k=0:N;W=2*pi*k/(N*dt);F=f*exp(-1i*t'*W)*dt;phase=angle(F);F=abs(F);subplot(3,1,1);plot(t,f);xlabel('t');ylabel('f(t)');title('f(t)');subplot(3,1,2);plot(W,F);xlabel('omega');ylabel('omega');title('f(t)µÄ¸µÀï

9、Ò¶±ä»»F(omega)');subplot(3,1,3);plot(W,phase);axis(0,200,-5,5);xlabel('omega');ylabel('omega');title('f(t)µÄ¸µÀïÒ¶±ä»»Ïàλ(omega)');（2）dt=0.005;t=0:dt:4; f=(t-2)/

10、2+1/2).*(t-2)>=-1)&(t-2)<=1);N=2000;k=0:N;W=2*pi*k/(N*dt);F=f*exp(-1i*(t+2)'*W)*dt;phase=angle(F);F=abs(F);subplot(3,1,1);plot(t,f);xlabel('t');ylabel('f(t)');title('f(t)');subplot(3,1,2);plot(W,F);xlabel('omega');ylabel('omega');title('f(t)&

11、#181;ĸµÀïÒ¶±ä»»F(omega)');subplot(3,1,3);plot(W,phase);axis(0,200,-5,5);xlabel('omega');ylabel('omega');title('f(t)µÄ¸µÀïÒ¶±ä»»Ïàλ(omega)&#

12、39;);10.5 如图所示电路为二阶低通滤波器。设R = sqrt（L/2C），L = 0.4H，C = 0.05F，R = 2欧，试用matlab编程绘制该系统频率响应H（jw）的幅频响应及相频响应曲线，并求出H(jw)的截止频率。b=0.1,0;a=0.02,-0.7,0;h,w=freqs(b,a,100);h1=abs(h);h2=angle(h);subplot(2,1,1);plot(w,h1);grid xlabel('½ÇƵÂÊ(omega)');ylabel('·ù&#

13、182;È');title('H(jomega)µÄ·ùƵÌØÐÔ');subplot(2,1,2);plot(w,h2*180/pi);gridxlabel('½ÇƵÂÊ(omega)');ylabel('Ïà루¶È£©');title('H(jomega)µÄÏàƵÌØÐÔ');