Impact of Array Orientations on Degrees of Freedom for Continuous Aperture Arrays (CAPA)

Abstract

Continuous aperture arrays (CAPA) revolutionize conventional multiple-input multiple-output (MIMO) systems by leveraging spatially continuous electromagnetic surfaces to enhance degrees of freedom (DoFs). In this letter, the impact of array orientations on near-field DoFs in CAPA plane-based system over the scalar Green's function channel is first characterized. Additionally, a comprehensive comparison of the derived near-field DoFs with the conventional far-field uniform plane wave (UPW)-based counterpart is provided. Subsequently, the impact of multi-polarization effect on DoFs performance is further explored. Specifically, the DoFs for the CAPA plane-based system over the dyadic Green's function-based channel are derived by incorporating the triple-polarized auto-correlation kernel function. Numerical results validate that 1) array orientations significantly impact near-field DoFs, and that the DoFs in uni-polarized planar CAPA can be enhanced via appropriately designing array orientations and apertures, 2) the incorporation of full polarization in the dyadic Green's function-based channel leads to a notable enhancement in DoFs performance in comparison to that of the scalar Green's function channel.