On the Potential of Multi-Mode Antennas for Direction-of-Arrival Estimation

A multimode antenna (MMA) can be an interesting alternative to a conventional phased antenna array for direction-of-arrival (DoA) estimation. By MMA, we mean a single physical radiator with multiple ports, which excite different characteristic modes. In contrast to phased arrays, a closed-form mathematical model of the antenna response, such as a steering vector, is not straightforward to define for MMAs. Instead, one has to rely on calibration measurement or electromagnetic field (EMF) simulation data, which is discrete. To perform DoA estimation, an array interpolation technique (AIT) and wavefield modeling (WM) are suggested as methods with inherent interpolation capabilities, fully taking antenna nonidealities like mutual coupling into account. We present a noncoherent DoA estimator for low-cost receivers and show how coherent DoA estimation and joint DoA and polarization estimation can be performed with MMAs. Utilizing these methods, we assess the DoA estimation performance of an MMA prototype in simulations for both the 2-D and 3-D cases. The results show that WM outperforms AIT for high signal-to-noise ratio. The coherent estimation is superior to noncoherent, especially in 3-D, because noncoherent suffers from estimation ambiguities. In conclusion, the DoA estimation with a single MMA is feasible and accurate.