Closed-loop subspace identification for vibration control of structure integrated antenna arrays

Structure integrated or conformal antenna arrays consist of several spatially distributed patches. Integrated in aircraft fuselages the array is excited by inherent engine and turbulent boundary layer induced vibrations. These disturbances lead to distortions of single patch orientation and thus to unknown phase differences in the patch signals. Smart-structures technology is the key to overcome this problem. Structure integrated sensors and actuators measure structural vibrations and induce annihilating vibrations which are calculated by a controller. This paper presents a closed-loop sub-space identification combined with a self-tuning controller approach. The objective is to identify the controlled plant operating in closed-loop in flight. Thereby, changes in the vibration behavior of the supporting structure due to temperature gradients e.g. are monitored. A subsequent re-synthesis of the controller by self-tuning guarantees optimal performance during the entire flight. For identification a two stage LQ decomposition is combined with a sequential LQ decomposition in order to handle large data sets. In experiments on an active plate demonstrator a parameter study leads to good identification results without degrading controller performance.