exa5_12.m

新版Matlab 7辅助信号处理技术与应用

%-----------------------------------------------------------------------------
% exa060304_blackmanbp1.m , for example 6.3.4
% use blackman window to design bandpass digital filter
%-----------------------------------------------------------------------------

Wpl = 0.4*pi;
Wph = 0.6*pi;
Wsl = 0.2*pi;
Wsh = 0.8*pi;
tr_width = min((Wpl-Wsl),(Wsh-Wph));  % 过渡带宽度
N = ceil(11*pi/tr_width)+1 % 滤波器长度
n = 0:1:N-1;
Wcl = (Wsl+Wpl)/2; % 理想低通滤波器的下截止频率
Wch = (Wsh+Wph)/2; % 理想低通滤波器的上截止频率
hd = ideal_bp1(Wcl,Wch,N); % 理想带通滤波器的单位冲激响应
w_bman = (blackman(N))'; % 汉宁窗
h = hd.*w_bman; % 截取得到实际的单位脉冲响应
[db,mag,pha,w] = freqz_m2(h,[1]); % 计算实际滤波器的幅度响应
delta_w = 2*pi/1000;
Ap= -(min(db(Wpl/delta_w+1:1:Wph/delta_w+1))) % 实际通带纹波
As = -round(max(db(Wsh/delta_w+1:1:501))) % 实际通带纹波
subplot(221)
stem(n,hd)
title('理想单位脉冲响应hd(n)')
subplot(222)
stem(n,w_bman)
title('汉宁窗w(n)')
subplot(223)
stem(n,h)
title('实际单位脉冲响应hd(n)')
subplot(224)
plot(w/pi,db)
title('幅度响应(dB)')
axis([0,1,-100,10])