MATLAB® and Its Applications in Engineering: [Based on MATLAB 7.5 (R2007b)]

12.18. Polar Plots

The polar plot of a sinusoidal transfer function G(jω) is a plot of the magnitude of G(jω) versus the phase angle of G(jω) on polar co-coordinates as ω is varied from zero to ∞. Thus, the polar plot is the locus of vectors |G(jω)|∠G(jω) as ω is varied from 0 to ∞. If the angle is measured from positive x-axis, it is positive in anti-clockwise direction, otherwise it is negative. The polar plot is very useful in determining the stability of a closed-loop system from its open loop frequency response.

Programming Tip 12.6

The polar plot is for the frequency range 0<w<∞ while the Nyquist plot is in the frequency range −∞<w<∞. In general, the polar plot is often called the Nyquist plot.

MATLAB can be used to obtain a polar plot ...