% dm10401
% 傅里葉變換的對稱性
dt = 0.1;                                  %采樣間隔
t = -20:dt:20;
f1 = sinc(t/pi);                           %計(jì)算抽樣函數(shù)f1(t)=Sa(t)的離散采樣點(diǎn)
f2 = pi*(Heaviside(t+1)-Heaviside(t-1)); %計(jì)算門函數(shù)f2(t) 的離散采樣點(diǎn)
N = 500;  %角頻率采樣點(diǎn)數(shù)
k = -N:N;
W = 2*pi*k/(N*dt);
F1 = dt*f1*exp(-j*t'*W);  %計(jì)算抽樣函數(shù)的頻譜
F2 = dt*f2*exp(-j*t'*W);  %計(jì)算門函數(shù)的頻譜
subplot(221);
plot(t,f1);
xlabel('t');
ylabel('f1(t)');
axis([-20 20 -0.5 1.1]);
subplot(222);
plot(W,F1);
axis([-2 2 -1 4]);
xlabel('w');
ylabel('F1(w)');
subplot(223);
plot(t,f2);
axis([-2 2 -1 4]);
xlabel('t');
ylabel('f2(t)');
subplot(224);
plot(W,F2);
axis([-20 20 -3 7]);
xlabel('w');
ylabel('F2(w)');
%End