Evaluation Method and Design Guidance for Direction-Finding Antenna Systems

A deterministic evaluation procedure for multiport direction-finding (DF) antennas is proposed. It is based on a DF uncertainty parameter, which describes how well different directions of arrival and polarizations are distinguishable. By investigating a simple antenna array, it is shown that the proposed parameter provides additional insights into the behavior of an antenna system when compared to established methods. Moreover, since the uncertainty parameter is calculated from a set of far fields, it is applicable to port far fields as well as Characteristic Modes (CMs). This finding is utilized to derive design guidance: starting with a set of CM far fields, the angular distribution of the uncertainty is investigated to verify that no ambiguities are present. Different sets of far fields are compared, and the differences regarding their DF behavior are visualized and explained using the uncertainty in conjunction with an estimate of the incident field. To quantify these differences, a key performance indicator (KPI) is introduced that summarizes the DF capabilities over a selected angular region. To demonstrate the design process, a multimode multiport antenna (M3PA) with three uncorrelated ports is developed, manufactured, and measured.