Measurement of Angle of Arrival for Airborne Collision Avoidance System

Abstract

It is necessary for Airborne Collision Avoidance System (ACAS) to have precise bearing information of the aircraft in the vicinity. In this paper, the use of a small radius circular array with Butler Matrix is discussed. When the radius of the array decreases, the mutual coupling increases. However, the relative phase relation among the elements is not changed by adjusting the output phase independently. The synthesized amplitude estimator, which transforms the phase information to the amplitude by forming combinations of the Matrix outputs, is presented. The error level for the direction finding of this system is nearly equal to that of the Maximum Likelihood Estimator.