Angle of Arrival Estimation Methods Using Spherical-Modes-Driven Multiport Antennas

Phased antenna arrays are commonly used to determine the Angle-of-Arrival (AoA) of radio signals. However, in cases where limitations on size and weight are a concern, a fresh approach involves using an innovative spherical mode-driven setup with Multiple-Input Multiple-Output (MIMO) antennas. These new antennas offer an unprecedented reduction in size. However, when traditional AoA estimation techniques are applied to multiport antennas with a nonlinear spatial configuration, the nuances of the algorithm's behavior merit exploration. This paper delves into finding the most effective AoA estimation method for MIMO antennas based on the spherical modes concept. In this work, various techniques for AoA estimation are evaluated, including the conventional Delay-and-Sum (DAS), the Minimum Variance Distortionless Response (MVDR), the subspace-based Multiple Signal Classifier (MUSIC), and the Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT). Numerical comparisons between the estimation techniques in the context of multiport antennas are discussed, with a specific focus on the balance between estimation accuracy and computational complexity. This study sheds light on the performance of the four above-mentioned techniques when applied to spherical modes-driven MIMO antennas, highlighting the most promising approaches for applications in compact Internet of Things (IoT) systems.