What Is a Bode Plot?

The Bode plot is named for its inventor, Hendrick Bode, an American engineer who worked at Bell Labs. It graphs the frequency response of a linear time-invariant (LTI) system. Both the amplitude and phase of the LTI system are plotted against the frequency. A logarithmic scale is used for frequency, as well as amplitude, which is measured in decibels (dB).

The Bode plot is a popular tool with control system engineers because it lets them achieve desired closed loop system performance by graphically shaping the open loop frequency response using clear and easy-to-understand rules. In addition, engineers can easily see the gain margin and phase margin of the control system.

Another use is for gaining insight into behavior of dynamic systems. For example, the plot clearly shows if the system is stable, how fast it will respond to commands, and if there are one or more frequencies where the system will have a resonance.