%用fwind2函數設計近似圓對稱二維帶通濾波器
%通帶頻率為[0.1  0.5]
%期望帶通頻率響應創建矩陣Hd
%用freqspace函數創建頻率范圍向量f1和f2. 
[f1,f2] = freqspace(21,'meshgrid');
Hd = ones(21); 
r = sqrt(f1.^2 + f2.^2);
Hd((r<0.1)|(r>0.5)) = 0;
colormap(jet(64))
mesh(f1,f2,Hd)

%由fspecial函數創建二維高斯窗函數
win = fspecial('gaussian',21,2);
win = win ./ max(win(:));  
% 窗函數的最大值為1
mesh(win)

%用上面生成的窗函數設計濾波器
h = fwind2(Hd,win);
freqz2(h)