Stability of feedback systems using dual Nyquist diagram

Abstract

This paper introduces a procedure for determing the stability of a feedback system using a dual Nyquist diagram. Such a diagram results when the characteristic equation of the system is interpreted to be the sum of two frequency-dependent functions F1(p) + F2(p) instead of the normal expression 1 + G(p)H(p). This diagram then consists of two polar plots; one plot represents the locus of one of the functions which is contained in the characteristic equation, and the other plot is the negative locus of the other function contained in the characteristic equation. Each of these curves may, if desired, be considered as an individual Nyquist diagram.