H ∞ control design for a seeker scan loop system

TwoH _∞ Controllers are presented for a seeker scan loop system which has model uncertainty and is subject to external disturbance. The controllers are designed using a newH _∞ control framework formulated by combining the mixed sensitivity and model matching approaches for one-and two-degree-of-freedom control structures. The proposed control methods are able to reflect not only frequency domain specifications but also time domain ones such as transient response characteristics and multivariable interaction between output channels, contrary to the mixed sensitivity problem. It is shown that the two-degree-of-freedomH _∞ controller offers better performance and robustness than one-degree-of-freedomH _∞ controller, but both controllers are very effective for the seeker scan loop system.