A polar diagram where the amplitude of the open-loop transfer function h0 is on a logarithmic scale, is presented. This gives a one-size-fits-all diagram with less need for zooming in and out, and no need for additional reasoning about infinite-radius encirclements when there are poles on the imaginary axis -- as opposed to what is often necessary with the standard polar (Nyquist-) diagram.
All properties needed for stability considerations are upheld, such as encirclements, gain and phase margins. The path for s in the loop transfer function is carefully chosen with regard to possible poles on the imaginary axis. Small excursions into the right half plane in the form of arcs of different-sized logarithmic spirals result in corresponding large but finite arcs for h0 that do not overlap in the logarithmic polar plots.
Note: the program at this stage works only for SISO and continuous-time systems.
· MATLAB Release: R13
· Control System Toolbox