一、线性相位。
并非所有的FIR滤波器都具有线性相位,只有当FIR滤波器的系数是对称的(包括偶对称和奇对称),才具有线性相位。
![](https://img-blog.csdnimg.cn/20210607213757113.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
根据FIR滤波器的阶数(M=点数N-1)及其对称特性,可以分成以下四种类型。
![](https://img-blog.csdnimg.cn/20210607213926901.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210607214156460.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210607214231476.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
其中,不同类型所适用的滤波器类型也不同。I型可以用于设计高通、低通、带通、带阻滤波器。
![](https://img-blog.csdnimg.cn/2021060721424844.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
FIR滤波器没有极点,只有零点。
其中零点的分布特点如下:
![](https://img-blog.csdnimg.cn/20210607214539285.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
第一种零点为4个;第二、三种为2个零点。第四种为1个零点。FIR滤波器的零点为这四种类型的零点的组合。
二、窗函数设计法。
![](https://img-blog.csdnimg.cn/20210607215116513.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210607215132700.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/2021060721532712.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
function [] = window_func() %四种窗函数
clear;close all;clc;
N = 30;
wk = rectWin(N);
subplot(221)
stem(wk);title('rect');
wk = hammingWin(N);
subplot(222)
stem(wk);title('hamming');
wk = hanningWin(N);
subplot(223)
stem(wk);title('hanning');
wk = blackmanWin(N);
subplot(224)
stem(wk);title('blackman');
function wk = rectWin(N) % 矩形窗
wk = ones(1,N);
function wk = hanningWin(N) % 汉宁窗
wk = ones(1,N);
for k=1:N
wk(k) = 0.5-0.5*cos((2*pi*k)/(N-1));
end
function wk = hammingWin(N) % 海明窗
wk = ones(1,N);
for k=1:N
wk(k) = 0.54-0.46*cos((2*pi*k)/(N-1));
end
function wk = blackmanWin(N) % 布莱克曼窗
wk = ones(1,N);
for k=1:N
wk(k) = 0.42-0.5*cos((2*pi*k)/(N-1)) + 0.08*cos((4*pi*k) / (N-1));
end
![](https://img-blog.csdnimg.cn/20210607220818885.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
三、频率抽样法。
![](https://img-blog.csdnimg.cn/2021060722141862.png)
![](https://img-blog.csdnimg.cn/20210607221539860.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/202106072216253.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
四、优化设计。
![](https://img-blog.csdnimg.cn/20210608214858224.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210608214914819.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210608214934668.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210608214958648.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210608215024507.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210608215046253.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
五、FIR滤波器与IIR滤波器比较。
![](https://img-blog.csdnimg.cn/20210608215210181.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
![](https://img-blog.csdnimg.cn/20210608215233256.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2szMzE5MjIxNjQ=,size_16,color_FFFFFF,t_70)
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