Mitigation of wing flexure induced errors for airborne direction-finding applications

Errors in array calibration are the dominant error source for direction finding (DF) in airborne platforms. This problem arises since wings in large surveillance aircraft exhibit significant flexure, and their actual instantaneous positions during array calibration and operational flight is likely to be quite different. Scattering from time-varying wing structures onto the belly mounted antennas therefore causes the array responses to deviate from the array calibration and gives rise to DF errors. We present a simple model for array manifold perturbations due to wing flexure that captures their effect. The model is physically motivated and has been validated using experiments on a scale-model aircraft in an anechoic chamber. Our model can be exploited to derive new versions of the classical DF estimation schemes including weighted subspace fitting (WSF).