Super-Beamforming in Holographic MIMO

TL;DR

This paper demonstrates that relaxing antenna spacing constraints in holographic MIMO arrays allows for super-beamforming gains that scale quadratically with the number of antennas, surpassing traditional limits.

Contribution

It reveals that mutual coupling can be exploited to achieve super-beams with quadratic gain scaling, challenging conventional array design assumptions.

Findings

Mutual coupling enables super-beamforming beyond traditional limits.

Quadratic gain scaling occurs with spacings slightly below half wavelength.

Super-beams are feasible when antenna losses are sufficiently small.

Abstract

The conventional linear scaling of beamforming gain with the number of antennas is not a fundamental physical limitation, but rather a consequence of the half-wavelength spacings that minimize mutual coupling. Relaxing this constraint facilitates beamforming gains exceeding those of uncoupled arrays along specific directions. This paper shows that, when antenna losses remain sufficiently small, mutual coupling enables the synthesis of super-beams whose endfire gain scales quadratically with the number of antennas. Notably, this quadratic scaling does not necessarily require vanishing spacings, but emerges for spacings slightly below half wavelength as the array aperture increases.