This paper investigates the frequency properties of linear active disturbance rejection control. For stable or critical stable second-order LTI plants, it proposes a new parameter tuning approach. The approach is proved that can guarantee the closed-loop has a given gain crossover frequency and a phase margin no less than a given value between 32 degrees and 73 degrees.

This paper investigates to control the double integrator with linear active disturbance rejection control and reports two results. First, there is a separation principle which means the dynamics of the state feedback and the error of extended state observer are completely decoupled. Second, with bandwidth method in which the observer bandwidth equals to the controller bandwidth, the closed-loop always has a phase margin of 31.89 degrees and a gain crossover frequency equals to the observer bandwidth, which can be set arbitrary.