The frequency response is the system's response to sinusoidal inputs. The output of
a linear time-invariant system to a sinusoidal input is a sinusoid of the same frequency
but with a different magnitude and phase. The magnitude and phase differences between the
input and output sinusoids are functions of frequency.
The most common ways to represent frequency reponse of a system are Bode plot and Nyquist
plot. A Bode plot shows the relationship between the magnitude and phase values of the
open-loop transfer function G(j*w) and input frequency(when the input frequency w goes from zero to infinity). A Nyquist plot is a representation of open-loop transfer function G(j*w) in s plane. The Nyquist plot allows us to predict the stability performance of a
closed-loop system by observing its open-loop behavior.
The functions below can be used to plot the Bode plot, Nyquist plot, and Nichols chart,
to claculate the gain and phase margin of a system or to calculate the value of open-loop
transfer function over a given frequency vector.
| Function | Description | ||
|---|---|---|---|
| Bode diagram | Plot the Bode frequency response of a system. | ||
| Gain and phase margin | Plot the gain and phase margins of a system. | ||
| Nichols chart | Plot the Nichols frequency response of a system. | ||
| Nyquist diagram | Plot the Nyquist frequency response of a system. | ||
| Frequency response | Calculate the system frequency response. |