MATLAB中的‘mkfilter命令设计贝塞尔型滤波器

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。该代码在运行时会产生预期的结果，但bessel过滤器实现除外。我收到了一个错误：

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

我尝试过多种方法，但似乎无法删除此错误。我已将下列全部代码包括在内：

%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')

提前谢谢。P.s，我对堆栈溢出很陌生，所以对格式化表示歉意。

Answer 1

贝塞尔滤波器的mkfilter中有一个错误，这会导致一阶和二阶贝塞尔滤波器返回此错误。您可以通过编辑mkfilter (使用edit mkfilter打开文件)来修复它：

从第58行开始：

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

将其改为：

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