Deep depression angle calibration of airborne direction finding arrays

Abstract

A system for calibrating airborne direction finding antenna arrays eliminates the problem of trying to maintain a constant depression angle when flying an airplane directly over a calibration antenna to collect deep depression angle data. The deep depression angle data necessary for calibration is provided by data from a scale model of the aircraft having a direction-finding array which simulates the actual direction-finding array on the aircraft. In order to collect deep depression angle data, the model is pivoted through 360° while maintaining a controlled depression angle. Thus, it is unnecessary for calibration to actually fly a plane to attempt to obtain deep depression angle measurements. In the subject system, only a single depression set of data is required from the aircraft. Thus, with the exception of baseline shallow depression angle data from this plane, the calibration data comes strictly from the scale model, which is much more easily obtained. Optimization techniques are used in which a set of data is collected from the airplane at one shallow depression angle which is used with the data collected from the scale model at the same shallow depression angle to derive a complex set of optimized weights that are then applied to the data collected from the model at the remainder of the depression angles to obtain the appropriate database for use on this aircraft for direction finding. In so doing, the aircraft need only be flown to establish data at a relatively shallow depression angle which can be easily collected by an aircraft flying in circles or banana pattern at some distance from the calibration antenna.

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