For a finite set of multi-input-multi-output(MIMO) linear time-invariant(LTI) plants, a method to tune gain/phase
margins in the output channels is presented. By using the theory of gain-phase margin tester, the question is translated into a simultaneous stabilization problem of a finite set of uncertain plants. An output feedback controller is designed for a plant based on continuous-time linear quadratic regulator(LQR) theory, and a method of periodic control is used to design a linear periodic controller for a finite set of plants. The controller can simultaneously provide gain margins as large as desired and phase margins of up to 90 degrees in the output channels of all feedback control loops for a finite set of plants. Simulation results show the effectiveness of the method.