设计一个低通数字滤波器，满足如下设计指标：

通带截止频率：0.2pi，通带波动：1dB

阻带截止频率：0.3pi，阻带衰减：15dB

要求：采用切比雪夫Ⅱ型滤波器原型，并分别采用脉冲响应不变变换法和双线性变换法进行设计，比较设计的结果，并进行分析

-Design a low pass digital filters that meet the following design specifications: passband cutoff frequency: 0.2pi, pass-band fluctuations: 1dB stopband cutoff frequency: 0.3pi, stop-band attenuation: 15dB requirements: use of Chebyshev filter prototypes with type Ⅱ and pulse response were the same transformation and bilinear transformation method designed to compare the results of the design and analysis