'mkfilter'命令在MATLAB中设计bessel类型过滤器

Question

我已经实现了一个简单的脚本，它比较了Butterworth，Chebyshev和Bessel过滤器的一系列过滤顺序。代码运行时会产生预期的结果，但bessel过滤器实现除外。我得到一个错误：

Error in FilterComparison (line 75) 
bes_1 = mkfilter(fc, 1, 'bessel'); 

我试过多个东西，但似乎无法删除此错误。我已经包含以下完整代码：

%Script to compare the responses of various analogue filters 
%including bessel, chebyshev and butterworth. 
%mkfilter command syntax 
%example = mkfilter (cutoff freq, order, 'type'); 

clear all 
close all 

%Cut off frequency 
fc = 2000; 

%Determines whether figures are displayed or not. 
%Silent = 1, no display 
silent = 1; 

%BUTTERWORTH FILTERS 
%1st order butterworth filter 
butter_1 = mkfilter(fc, 1, 'butterw'); 

%2nd order butterworth filter 
butter_2 = mkfilter(fc, 2, 'butterw'); 

%3rd order butterworth filter 
butter_3 = mkfilter(fc, 3, 'butterw'); 

%4th order butterworth filter 
butter_4 = mkfilter(fc, 4, 'butterw'); 

%5th order butterworth filter 
butter_5 = mkfilter(fc, 5, 'butterw'); 

%6th order butterworth filter 
butter_6 = mkfilter(fc, 6, 'butterw'); 

%Bode plot 
if ~silent 
    figure(1) 
    bode(butter_1, 'red',butter_2, 'blue',butter_3, 'green',butter_4, 'cyan',butter_5,  'black',butter_6, 'magenta') 
    legend('n = 1','n = 2','n = 3','n = 4', 'n = 5', 'n = 6') 
end 

%CHEBYSHEV FILTERS 
%1st order chebyshev filter 
cheby_1 = mkfilter(fc, 1, 'Cheby', 2); 

%2nd order chebyshev filter 
cheby_2 = mkfilter(fc, 2, 'Cheby', 2); 

%3rd order chebyshev filter 
cheby_3 = mkfilter(fc, 3, 'Cheby', 2); 

%4th order chebyshev filter 
cheby_4 = mkfilter(fc, 4, 'Cheby', 2); 

%5th order chebyshev filter 
cheby_5 = mkfilter(fc, 5, 'Cheby', 2); 

%6th order chebyshev filter 
cheby_6 = mkfilter(fc, 6, 'Cheby', 2); 

%Bode plot 
if ~silent 
    figure(2) %open figure 2 
    bode(cheby_1, 'red',cheby_2, 'blue',cheby_3, 'green',cheby_4, 'cyan',cheby_5, 'black',cheby_6, 'magenta') 
    legend('n = 1','n = 2','n = 3','n = 4', 'n = 5', 'n = 6') 
end 

%BESSEL FILTERS 
%1st order bessel filter 
bes_1 = mkfilter(fc, 1, 'bessel'); 

%2nd order bessel filter 
bes_2 = mkfilter(fc, 2, 'bessel'); 

%3rd order bessel filter 
bes_3 = mkfilter(fc, 3, 'bessel'); 

%4th order bessel filter 
bes_4 = mkfilter(fc, 4, 'bessel'); 

%5th order bessel filter 
bes_5 = mkfilter(fc, 5, 'bessel'); 

%6th order bessel filter 
bes_6 = mkfilter(fc, 6, 'bessel'); 

%Bode Plot 
figure(3) 
bode(bes_1, 'red',bes_2, 'blue',bes_3, 'green',bes_4, 'cyan',bes_5, 'black',bes_6,   'magenta') 
legend('n = 1','n = 2','n = 3','n = 4', 'n = 5', 'n = 6') 

%Plot 3rd order filters for comparison 
figure (4) 
bode(cheby_3, 'red', bes_3, 'blue', butter_3, 'green') 
legend('Chebyshev', 'Bessel', 'Butterworth') 

在此先感谢。 P.s，我是新来堆栈溢出，所以格式化的道歉。

Answer 1

bessel过滤器的mkfilter中有一个错误，导致第一和第二阶贝赛尔过滤器返回此错误。

在第58行开始：： 您可以通过编辑mkfilter（使用edit mkfilter打开文件）修复

if ord == 1, 
    sys = nd2sys(1,b1); 
elseif ord == 2, 
    sys = nd2sys(1,b2); 
... 

更改到这一点：

if ord == 1, 
    sys = tf(1,b1); 
elseif ord == 2, 
    sys = tf(1,b2); 
...