设计一个模拟巴特沃特低通滤波器，它在30rad/s处具有1dB或更好的波动，在50rad/s处具有至少30dB的衰减。求出级联形式的系统函数，画出滤波器的幅度响应、对数幅度响应、相位响应和脉冲响应图。-Design an analog low-pass filter of Bart Walter, it 30rad/s, at 1dB or better fluctuations in 50rad/s, at least 30dB of attenuation. Calculate the system function of the cascade form, draw the filter s amplitude response, logarithmic amplitude response, phase response and impulse response diagram.