Theory of Broadband Super Sensitivity Receiving With Closely Spaced Antenna Arrays

Antenna arrays can achieve better signal-to-noise/interference ratios in receivers, but the spacing among the antenna elements is typically required to be around half wavelength to avoid mutual coupling. Closely spaced ( {d} \lt 0.1~{\lambda } ) antenna elements with multiport matching networks can overcome the mutual coupling at the price of reduced impedance matching bandwidth. In this article, it is proposed to use a combination of active direct matching for the antenna and a mode-based beamforming signal processing approach at the receiver to achieve a broadband gain of signal-to-noise ratio (SNR) that approaches the theoretical directivity of the array. The theory of such "supergain" reception is presented for a small number of infinitesimal dipole antennas, and numerical simulations are carried out to demonstrate an SNR improvement that is consistent with the theoretical prediction. The proposed approach avoids the loss and complexity of using multiport matching networks yet can achieve an SNR gain over a broad bandwidth. It may find applications in wireless sensing that demands high sensitivity from antenna arrays in small form factors.