ABSTRACT
This chapter discusses systems whose performance is limited by uncertainties in the plant at high frequencies. It reviews the typical characteristics of these systems and reviews the performance of the Bode single-loop system. The chapter introduces some material regarding stability margins in band-pass systems, emphasizing the role of simulation to verify global stability. It presents something entirely different, which is the use of nonlinear multi-loop feedback for the single-input single-output system with high-frequency plant uncertainty. Nonlinear multi-loop methods may be applicable to other problems in filtering, estimation, and prediction. Careful attention must be paid to the phase uncertainty associated with the gain peaks of the uncertainty region to keep the gain deviations of the combined response small compared to the stability margins, and the closed-loop response close to the central line.
