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

Calibration errors are the dominant error source for direction nding (DF) from airborne platforms. Calibration of the array manifold is done with the wings in an unknown position. Wing movements during ight perturbs the array manifold from its calibrated value, causing errors in the direction nding. We present a direction nding algorithm that compensates for variations in wing exure. The algorithm relies on a physically motivated model that captures the gross behavior of the mani-fold perturbations. The model has been validated using experiments on a model aircraft in an anechoic chamber. The structure of the model can be exploited in estimation schemes such as weighted subspace tting, leading to improved DF accuracy. With correct model parameters the eeect of the manifold perturbation is, in fact, fully neutralized. The properties of the new scheme are demonstrated through analysis and simulation. 1. The Problem One of the major challenges of direction nding using belly-mounted antenna arrays on airborne data collection platforms is the variability in the near-eld scattering from the aircraft structure. Flexure of the aircraft structure can perturb the array manifold. To achieve accurate direction nding, one measures or calibrates the response of the antenna array in ight over the full operating azimuth range. This array calibration captures the array response including the scattering from the aircraft structure, but only at the current position of the aircraft structure. Most of the fuselage is fairly rigid; however, the position of the wing tips of an aircraft may move more than a meter vertically relative to the fuselage during reproduce and distribute reprints for governmental purposes notwithstanding any copyrights notation hereon. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the oocial policies or endorsements, either express or implied, of the Advanced Research Projects Agency or the U.S. Government.