# Exploring the Advantages of Sparse Arrays in Near-Field XL-MIMO Systems: Beam Analysis and EDoF Function

arXiv: https://arxiv.org/abs/2501.09234 · HTML: https://mlsanity.com/paper/2501.09234/

## Key facts

- Cited by 1 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 16 Jan 2025.

## Built on by (most cited first, 1 of 1)

- [ORCA: Orchestrated Reasoning with Collaborative Agents for Document Visual Question Answering](https://mlsanity.com/paper/2603.02438/) (2026)

## Abstract (arXiv)

This paper investigates near-field XL-MIMO systems with sparse uniform planar arrays (UPAs). Based on the Green's function-based channel model, the paper derives closed-form expressions for the signal beam power when the distance coordinate or the angular coordinates varies with respective to the focused position. Based on that, closed-form expressions for the lobe length and the suppressing ratio are obtained, indicating that both the distance-focusing property and the grating lobe behavior can be enhanced as the focal distance decreases or the antenna spacing increases. Furthermore, the paper introduces a crucial constraint on system parameters, under which effective degrees-of-freedom (EDoF) of XL-MIMO systems with sparse UPAs can be precisely estimated. Then, the paper proposes an algorithm to obtain a closed-form expression, which can estimate EDoF with high accuracy and low computational complexity. The numerical results verifies the correctness of the main results of this paper.