On the Unilateral Approximation Condition with Linear Arrays in Near-Field NLoS Propagation

2026-07-26

AI Summary

This study investigates the validity of the unidirectional approximation—neglecting the electromagnetic back-reaction from the receiver on the transmitter—in near-field non-line-of-sight (NLoS) propagation scenarios involving large-scale linear antenna arrays. Leveraging multiport communication theory, electromagnetic reciprocity, large-array modeling, and statistical averaging techniques, the work theoretically demonstrates for the first time that, in the asymptotic regime where the number of antennas tends to infinity, the unidirectional approximation holds in a mean-square sense. This result applies universally to both discrete arrays with fixed inter-element spacing and continuous apertures with fixed physical size. The findings provide rigorous theoretical justification for the physically consistent application of Rayleigh fading models in near-field wireless systems.

Abstract

This paper investigates the validity of the unilateral approximation in near-field non-line-of-sight (NLoS) propagation for large-scale linear antenna arrays. Utilizing multiport communication theory, the study evaluates whether the electromagnetic interaction from the receiver back to the transmitter can be neglected. The analysis examines both discrete arrays with fixed spacing and continuous arrays with fixed aperture as the number of antennas increases. Results show the approximation is asymptotically satisfied on average for both cases. This provides a theoretical foundation for using correlated Rayleigh fading models in physically consistent next-generation wireless systems.

Problem

• unilateral approximation
• near-field
• NLoS propagation
• linear arrays
• electromagnetic interaction

Innovation

• unilateral approximation
• near-field NLoS propagation
• linear antenna arrays
• multiport communication theory
• correlated Rayleigh fading