现代控制理论
频率特性
系统的频率特性可以用Nyquist 图（极坐标图）或者用其幅值（比）和相角为因变量，输入信号的频率为自变量绘图。在绘图时通常幅值（比）用分贝表示，相角用度表示，输入信号的频率按常用对数取值。以上这两个图称为伯德图（以H. W. Bode命名）。可以用计算机绘出精确的伯德图。在本文中将讨论用手工绘制的技巧简单而快速地绘制直线渐进线图。
系统传递函数的伯德图可以用于确定各种输入（包括阶跃输入）下系统的稳态响应。因为频率响应为稳态响应，所以系统必须是稳定且其稳定性必须在绘制伯德图之前确定。
Modern Control Theory
Frequency transfer function of a system
the frequency transfer function of a system or of its function can be presented either by the single Nyquist diagram( a polar plot) or by plots of the amplitude ratio and the phase angle against the input(forcing) frequency. It is customary to plot the amplitude ratio in decibels and the phase angle in degree against the common logarithm of the input frequency. In this form, the two plots are known as Bode plots(after H.W.Bode). There are exact Bode plots, which are best prepared with a computer, and straight-line asymptotic plots, which can be quickly and easily sketched or plotted by hand using the techniques to be developed and discussed in this article.
3500字
