Evaluation and Design of Multi-Mode Multi-Port Direction Finding Antennas

In both communication and direction finding, the potential of multi-mode multi-port antennas $\left(\mathrm{M}^{3} \mathrm{PA}\right)$ has recently received increased attention. Here, multiple ports are implemented on a single conducting structure by utilizing the Theory of Characteristic Modes (TCM). In contrast to traditional antenna arrays, no analytical model is available for $\mathrm{M}^{3} \mathrm{PA}$. Therefore, ambiguities in the direction finding cannot be predicted using geometrical considerations alone. In order to avoid these ambiguities in the antenna design process, a suited evaluation procedure is required. Established methods like the Cramer-Rao-Bound and the spectrum of the MUSIC-algorithm provide either no information on ambiguities or tend to suppress them. Therefore, the direction finding uncertainty parameter [1] is used: