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. V& P3 W' q7 Q周期方波的表达式我就不提炼了，既然你来看文章了，我就不信你周期方波都不知道。0 t9 O( `0 R1 q; }. Q; G
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占空比定义为：L/N，N为周期，下面我们对 L = 5，N = 20； L = 5，N = 40；L = 5，N = 60；L = 7，N = 60分别画出它们的DFS图作比较。
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我觉得有必要先把对应的周期方波给出来（每幅图都只给出一个周期）：
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* e" A& P# B% ?) p- D1 e; ]# ~- clc;clear;close all;
- % Periodic square wave parameters L = 5,N = 20
- L = 5;
- N = 20;
- n = 0:N-1;
- xn = [ones(1,L),zeros(1,N-L)];
- subplot(2,2,1)
- stem(n,xn);
- title('L = 5,N = 20');
- xlabel('n');ylabel('xtilde(n)');
- % Periodic square wave parameters L = 5,N = 40
- L = 5;
- N = 40;
- n = 0:N-1;
- xn = [ones(1,L),zeros(1,N-L)];
- subplot(2,2,2)
- stem(n,xn);
- title('L = 5,N = 20');
- xlabel('n');ylabel('xtilde(n)');
- % Periodic square wave parameters L = 5,N = 60
- L = 5;
- N = 60;
- n = 0:N-1;
- xn = [ones(1,L),zeros(1,N-L)];
- subplot(2,2,3)
- stem(n,xn);
- title('L = 5,N = 20');
- xlabel('n');ylabel('xtilde(n)');
- % Periodic square wave parameters L = 7,N = 60
- L = 7;
- N = 60;
- n = 0:N-1;
- xn = [ones(1,L),zeros(1,N-L)];
- subplot(2,2,4)
- stem(n,xn);
- title('L = 5,N = 20');
- xlabel('n');ylabel('xtilde(n)');
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上面程序中的DFS函数定义在另一篇博文中：【 MATLAB 】离散傅里叶级数（DFS）及 IDFS 的 MATLAB 实现) f8 ^% n9 R% Q! ]) }- c6 w
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直接给出MATLAB脚本：
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- clc;clear;close all;
- % Periodic square wave parameters L = 5,N = 20
- L = 5;
- N = 20;
- k = [-N/2:N/2];
- xn = [ones(1,L),zeros(1,N-L)];
- Xk = dfs(xn,N);
- magXk = abs( [ Xk(N/2+1:N),Xk(1:N/2+1) ] );
- subplot(2,2,1)
- stem(k,magXk);
- title('DFS of Square: L = 5,N = 20');
- xlabel('k');ylabel('Xtilde(k)');
- % Periodic square wave parameters L = 5,N = 40
- L = 5;
- N = 40;
- k = [-N/2:N/2];
- xn = [ones(1,L),zeros(1,N-L)];
- Xk = dfs(xn,N);
- magXk = abs( [ Xk(N/2+1:N),Xk(1:N/2+1) ] );
- subplot(2,2,2)
- stem(k,magXk);
- title('DFS of Square: L = 5,N = 40');
- xlabel('k');ylabel('Xtilde(k)');
- % Periodic square wave parameters L = 5,N = 60
- L = 5;
- N = 60;
- k = [-N/2:N/2];
- xn = [ones(1,L),zeros(1,N-L)];
- Xk = dfs(xn,N);
- magXk = abs( [ Xk(N/2+1:N),Xk(1:N/2+1) ] );
- subplot(2,2,3)
- stem(k,magXk);
- title('DFS of Square: L = 5,N = 60');
- xlabel('k');ylabel('Xtilde(k)');
- % Periodic square wave parameters L = 7,N = 60
- L = 7;
- N = 60;
- k = [-N/2:N/2];
- xn = [ones(1,L),zeros(1,N-L)];
- Xk = dfs(xn,N);
- magXk = abs( [ Xk(N/2+1:N),Xk(1:N/2+1) ] );
- subplot(2,2,4)
- stem(k,magXk);
- title('DFS of Square: L = 7,N = 60');
- xlabel('k');ylabel('Xtilde(k)');
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发表于 2019-10-30 11:22
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反对！