The Circular Antenna Array Framework for Near-field Radio Sensing

A novel near-field (NF) radio sensing antenna array design framework is proposed, where the circular antenna arrays are exploited to be compatible with the propagation of the spherical wavefronts. The uniform circular antenna (UCA) and uniform concentric circular antenna (UCCA) are investigated to investigate the impact of antenna geometry design on radio sensing performance. By exploiting the uniform spherical wavefront (USW) model in NF propagation, the approximate Cramér-Rao bound (CRB) expressions of both the angle and distance estimation are given. To further evaluate the impact of antenna array geometry design, the corresponding closed-form CRB expression with the isotropic beamforming design is derived. Numerical results validated that the proposed approximate CRB expressions are close to the numerical results, which indicates that the Fisher Information Matrix (FIM) about angle and distance in NF can be approximated as a diagonal matrix. When the target is located in the co-plane of the antenna array, the angle and distance estimation performance of UCA are usually better than UCCA with the same aperture size and antennas.