A Cupola-Shaped Multimode Multiport Antenna for Aerial Direction Finding

A multimode multiport antenna, consisting of a single conducting structure, is proposed for use with the airborne collision avoidance system. Its cupola-shaped surface is selected from a set of aerodynamically suitable and symmetric structures. The selection is based on a presented statistical evaluation procedure for direction-finding (DF) antennas and algorithms, which predicts the root-mean-square error of the estimation using characteristic modes. A demonstrator antenna and feed network are manufactured, and its three ports are measured in an anechoic chamber. The results match the intended far-fields of an electric monopole and two magnetic dipoles. The presented flight test results show that the antenna is capable of unambiguous DF across the desired angular range in a real-world environment.