FREQUENCY DOMAIN CONDITIONS FOR STRICTLY POSITIVE REAL FUNCTIONS.

Abstract

Frequency-domain conditions for strictly positive real (SPR) functions which appear in literature are often only necessary or only sufficient. This point is raised by B. D. O. Anderson and S. Vongpanitlerd (1973), and J. H. Taylor (1974) where necessary and sufficient conditions in the s-domain are given for a transfer function to be SPR. The points raised by the said authors are clarified further by giving necessary and sufficient conditions in the frequency domain for transfer functions to be SPR. These frequency-domain conditions are easier to test than those given in the s-domain or time domain.