Abstract—This paper presents an application of controller design using sinusoidal-input describing function (SIDF) for a two-link robotic orthosis, which is a non-linear multivariable system. A controller based on closed-form solution of lead-lag compensator is generated via unified approached technique. The performance of the controller is evaluated with step response, tracking and decoupling qualities as well as the trajectories tracking and this is compared with the conventional PID controller.