AbstractThis paper introduces some recently developed frequency‐domain design techniques that are effective in the design of control systems that are required to be robust under parametric uncertainty. We have extended the well‐known classical control tools (i.e., Nyquist plot, Bode plot, and Nichols chart) developed for a fixed plant to the domain offamiliesof plants where the uncertain parameter varies in intervals. Using this new family of plots, classical control design techniques can be used to design robust control systems. The technique is illustrated by examp