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1、四、实验容1、求出下图中周期方波信号的频谱,并参照例3-1,并画出频谱图。(A=1,τ=0.5,T1=1)是在把周期信号在时域上右移了0.25个单位,频域不变MATLAB实现傅里叶级数计算的程序如下:dt=0.01;T1=1;w1=2*pi/T1;t=-T1:dt:T1;tau=0.5;A=1;f=A*(heaviside(t+0)-heaviside(t-tau));subplot(2,1,1)plot(t,f)axis([-T1,T1,-0.1,1.1])title('f(t)时域波形')N=10;n=-N:N;Fn=f*exp(-j*t'*w1*n)*dt/T1;subplo
2、t(2,1,2)stem(n,Fn)holdondw=0.01;w=-N*w1:dw:N*w1;F=A*tau/T1*sinc(w*tau/pi);plot(w/w1,F,'--')title('傅里叶级数F_n')1)脉冲宽度τ=0.5保持不变,分别取T1=2τ,T0=4τ和T0=8τ,分别绘制相应的频谱图,并讨论周期T1与频谱的关系。T1越大,频谱图的幅度越小,衰减速度增快。T1=2τT1=1dt=0.01;T1=1;w1=2*pi/T1;t=-T1:dt:T1;tau=0.5;A=1;f=A*(heaviside(t+0)-heaviside(t-tau));subplot(
3、2,1,1)plot(t,f)axis([-T1,T1,-0.1,1.1])title('f(t)时域波形')N=10;n=-N:N;Fn=f*exp(-j*t'*w1*n)*dt/T1;subplot(2,1,2)stem(n,Fn)holdondw=0.01;w=-N*w1:dw:N*w1;F=A*tau/T1*sinc(w*tau/pi);plot(w/w1,F,'--')title('傅里叶级数F_n')T0=4τT0=2T1=2τT1=1dt=0.01;T1=2;w1=2*pi/T1;t=-T1:dt:T1;tau=0.5;A=1;f=A*(heaviside(t+0)-
4、heaviside(t-tau));subplot(2,1,1)plot(t,f)axis([-T1,T1,-0.1,1.1])title('f(t)时域波形')N=10;n=-N:N;Fn=f*exp(-j*t'*w1*n)*dt/T1;subplot(2,1,2)stem(n,Fn)holdondw=0.01;w=-N*w1:dw:N*w1;F=A*tau/T1*sinc(w*tau/pi);plot(w/w1,F,'--')title('傅里叶级数F_n')T0=8ττ=0.5t0=4dt=0.01;T1=4;w1=2*pi/T1;t=-T1:dt:T1;tau=0.5;A=
5、1;f=A*(heaviside(t+0)-heaviside(t-tau));subplot(2,1,1)plot(t,f)axis([-T1,T1,-0.1,1.1])title('f(t)时域波形')N=10;n=-N:N;Fn=f*exp(-j*t'*w1*n)*dt/T1;subplot(2,1,2)stem(n,Fn)holdondw=0.01;w=-N*w1:dw:N*w1;F=A*tau/T1*sinc(w*tau/pi);plot(w/w1,F,'--')title('傅里叶级数F_n')2)脉冲周期T1=1保持不变,分别取τ=0.75、τ=0.5和τ=0.25,
6、分别绘制相应的频谱图,并讨论脉冲宽度τ与频谱的关系。Τ越大。幅度越大dt=0.01;T1=1;w1=2*pi/T1;t=-T1:dt:T1;tau=0.75;A=1;f=A*(heaviside(t+0)-heaviside(t-tau));subplot(2,1,1)plot(t,f)axis([-T1,T1,-0.1,1.1])title('f(t)时域波形')N=10;n=-N:N;Fn=f*exp(-j*t'*w1*n)*dt/T1;subplot(2,1,2)stem(n,Fn)holdondw=0.01;w=-N*w1:dw:N*w1;F=A*tau/T1*sinc(w
7、*tau/pi);plot(w/w1,F,'--')title('傅里叶级数F_n')dt=0.01;T1=1;w1=2*pi/T1;t=-T1:dt:T1;tau=0.5;A=1;f=A*(heaviside(t+0)-heaviside(t-tau));subplot(2,1,1)plot(t,f)axis([-T1,T1,-0.1,1.1])title('f(t)时域波形')N=10;n=-N:N;Fn=f*exp(-j*t'*w1*n)*dt/T1;subpl