Robustness of pole-clustering in a ring for structured perturbation systems

A simple approach is proposed to ensure that all poles of an uncertain system are clustered in a prescribed ring. The explicit bounds on linear time-invariant structured perturbations are obtained. Under these allowable highly structured perturbations, both stability robustness and certain performance robustness will thus be ensured. In the literature, as far as we are aware, little effort has been devoted to investigating pole-clustering robustness in such regions.