Straight-Line Approximations for Phase-Angle Plots

There are several graphical means being used in the frequency domain to predict and adjust control system performance, two of which are the log-magnitude plot and the phase-angle plot. In teaching the former of these in undergraduate curricula, extensive use is made of straight-line approximations to the log magnitude, whereas no correspondingly simple approximation for phase angle has been made available. This paper offers an effective procedure for approximating the phase-angle plot by straight lines in much the same way that the log-magnitude plots are approximated.