周期信号频谱分析
4/(w2 + 4)
10.9
0.80.70.60.50.40.30.20.10-6
-4
-2
0w
2
4
6
f(t)=e^-2|t|的fourier 变换
matlab 程序 syms t;
f=fourier(exp(-2*abs(t))); ezplot(f)
(2 exp(-3 t) heaviside(t))/3
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
t
2/(3 abs(w i + 3))
0.20.150.1
-6
-4
-2
0w
2
4
6
f(t)=(2/3)e^-3tU(t)的波形及其幅频特性曲线
matlab 程序: syms t v w f
f=2/3*exp(-3*t)*sym('heaviside(t)'); F=fourier(f); subplot(2,1,1); ezplot(f);
subplot(2,1,2); ezplot(abs(F));
F (jw )=1/(1+w^2) 的傅里叶逆变换
>> syms t w
>> ifourier(1/(1+w^2),t) ans =
(pi*exp(-t)*heaviside(t) + pi*heaviside(-t)*exp(t))/(2*pi)
0.5f (t )
-50.4F (j w )
-4-3-2-1
0t
12345
0.2
0-81000
-100
-8
-6-4-2
0w
2468
-6-4-202468
f(t)=(1/2)*e^-2tU(t)的频谱 matlab 程序
r=0.02;t=-5:r:5;N=200;Y=2*pi;k=-N:N;w=k*Y/N; f1=1/2*exp(-2*t).*stepfun(t,0); F=r*f1*exp(-j*t'*w);
F1=abs(F);P1=angle(F);subplot(3,1,1);plot(t,f1);grid xlabel('t');ylabel('f(t)');title('f(t)');subplot(3,1,2)
plot(w,F1);xlabel('w');grid;ylabel('F(jw)');subplot(3,1,3) plot(w,P1*180/pi);grid;xlable('w');ylabel('相位(度)');
0.5f (t )
-50.4F (j w )
-4-3-2-1
0t
12345
0.2
0-82000
-200
-8
-6-4-2
0w
2468
-6-4-202468
f(t-1)的频谱 matlab 程序如下
>> r=0.02;t=-5:r:5;N=200;Y=2*pi;k=-N:N;w=k*Y/N; f1=1/2*exp(-2*(t-1)).*stepfun(t,1); F=r*f1*exp(-j*t'*w);
F1=abs(F);P1=angle(F);subplot(3,1,1);plot(t,f1);grid xlabel('t');ylabel('f(t)');title('f(t-1)');subplot(3,1,2)
plot(w,F1);xlabel('w');grid on;ylabel('F(jw)');subplot(3,1,3) plot(w,P1*180/pi);grid;xlable('w');ylabel('相位(度)');
(cos(w) i + sin(w))/w - (cos(w) i - sin(w))/w
2
1.5
1
0.5
-0.5
-6
-4
-2
0w
2
4
6
f(t)=U(t+1)-U(t-1)的fourier 变换表达式: F(jw)=(1/w)*(icosw+sinw)-(1/w)*(icosw-sinw )
Matlab 程序 >> syms t;
f=heaviside(t+1)-heaviside(t-1); F=fourier(f); ezplot(F);
1f (t )
0.5
0-100.4
-8-6-4-2
0t
246810
F (j w )
0.2
0-81000
-100
-8
-6-4-2
0w
2468
-6-4-202468
f(t)=e^-3tU(t)的频谱图
matlab 程序
r=0.02;t=-10:r:10;N=200;Y=2*pi;k=-N:N;w=k*Y/N; f1=exp(-3*t).*stepfun(t,0); F=r*f1*exp(-j*t'*w);
F1=abs(F);P1=angle(F);subplot(3,1,1);plot(t,f1);grid xlabel('t');ylabel('f(t)');title('f(t)');subplot(3,1,2)
plot(w,F1);xlabel('w');grid;ylabel('F(jw)');subplot(3,1,3) plot(w,P1*180/pi);grid;xlable('w');ylabel('相位(度)');
1f (t )
0.5
0-100.4
-8-6-4-2
0t
246810
F (j w )
0.2
0-82000
-200
-8
-6-4-2
0w
2468
-6-4-202468
f(t-4)的频谱图
matlab 程序
r=0.02;t=-10:r:10;N=200;Y=2*pi;k=-N:N;w=k*Y/N; f1=exp(-3*(t-4)).*stepfun(t,4); F=r*f1*exp(-j*t'*w);
F1=abs(F);P1=angle(F);subplot(3,1,1);plot(t,f1);grid xlabel('t');ylabel('f(t)');title('f(t)');subplot(3,1,2)
plot(w,F1);xlabel('w');grid;ylabel('F(jw)');subplot(3,1,3) plot(w,P1*180/pi);grid;xlable('w');ylabel('相位(度)');
1f 1(t )
-1-100.4
-8-6-4-2
0t
246810
F (j w )
0.2
0-81000
-100
-8
-6-4-2
0w
2468
-6-4-202468
f1(t)=f(t)*e^-j4t的频谱图
matlab 程序
r=0.02;t=-10:r:10;N=200;Y=2*pi;k=-N:N;w=k*Y/N; f1=exp(-3*t).*stepfun(t,0).*exp(-j*4*t); F=r*f1*exp(-j*t'*w);
F1=abs(F);P1=angle(F);subplot(3,1,1);plot(t,f1);grid xlabel('t');ylabel('f1(t)');title('f1(t)');subplot(3,1,2)
plot(w,F1);xlabel('w');grid;ylabel('F(jw)');subplot(3,1,3) plot(w,P1*180/pi);grid;xlable('w');ylabel('相位(度)');