低通贝塞尔滤波器的频率响应

设计一个五阶模拟低通贝塞尔滤波器，其群延迟在频率达到 $1 0^{4}$ 弧度/秒前大致恒定。使用 freqs 绘制滤波器的幅值和相位响应。

wc = 10000;
[b,a] = besself(5,wc);
freqs(b,a)

Figure contains 2 axes objects. Axes object 1 with xlabel Frequency (rad/s), ylabel Phase (degrees) contains an object of type line. Axes object 2 with xlabel Frequency (rad/s), ylabel Magnitude contains an object of type line.

计算展开相位响应的导数的负值以得到滤波器的群延迟响应。绘制群延迟，以验证它在不超过截止频率前大致恒定。

[h,w] = freqs(b,a);
grpdel = -diff(unwrap(angle(h)))./diff(w);

clf
loglog(w(2:end),grpdel)
xlabel("Frequency (rad/s)")
ylabel("Group delay (s)")
xline(wc)
grid on

Figure contains an axes object. The axes object with xlabel Frequency (rad/s), ylabel Group delay (s) contains 2 objects of type line, constantline.

另请参阅

besself | freqs