Localization systems play a crucial role in various IoT applications; however, traditional techniques require significant computational resources and complex hardware, making them impractical for resource-limited devices. This paper introduces a dual-pronged approach that addresses these challenges by focusing on reducing computational complexity, optimizing tag design, and enhancing Direction-of-Arrival (DoA) estimation accuracy in real-world scenarios. A Received Signal Strength Difference (RSSD)-based DoA method using a tilted array configuration is proposed, requiring only a single subtraction for RSSD calculation. A calibration technique mitigates anchor-tag misalignment, reducing Root-Mean-Square Error (RMSE) from 12.50 to 60. Furthermore, antenna directivity and tilting angle are analyzed, introducing RSSD slope as a metric for design-performance optimization. Experiments confirm that higher RSSD slopes improve estimation accuracy and noise robustness. These findings enable efficient localization solutions for small, power-constrained devices, paving the way for real-world IoT applications.

We characterize three near-field sub-regions for phased array antennas by elaborating on the boundaries Fraunhofer, radial-focal, and non-radiating distances. The Fraunhofer distance which is the boundary between near and far field has been well studied in the literature on the principal axis (PA) of single-element center-fed antennas, where PA denotes the axis perpendicular to the antenna surface passing from the antenna center. The results are also valid for phased arrays if the PA coincides with the boresight, which is not commonly the case in practice. In this work, we completely characterize the Fraunhofer distance by considering various angles between the PA and the boresight. For the radial-focal distance, below which beamfocusing is feasible in the radial domain, a formal characterization of the corresponding region based on the general model of near-field channels (GNC) is missing in the literature. We investigate this and elaborate that the maximum-ratio-transmission (MRT) beamforming based on the simple uniform spherical wave (USW) channel model results in a radial gap between the achieved and the desired focal points. While the gap vanishes when the array size N becomes sufficiently large, we propose a practical algorithm to remove this gap in the non-asymptotic case when N is not very large. Finally, the non-radiating distance, below which the reactive power dominates active power, has been studied in the literature for single-element antennas. We analytically explore this for phased arrays and show how different excitation phases of the antenna array impact it. We also clarify some misconceptions about the non-radiating and Fresnel distances prevailing in the literature.