Super-Beamforming in Holographic MIMO
This work provides a new theoretical understanding of beamforming limits for antenna array designers, potentially enabling higher gain in compact arrays.
The paper demonstrates that mutual coupling in holographic MIMO arrays can enable super-beams with endfire gain scaling quadratically with the number of antennas, provided antenna losses are small, challenging the conventional linear scaling assumption.
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.