Theory of Broadband Super Sensitivity Receiving with Closely Spaced Antenna Arrays

Antenna arrays can achieve a better signal to noise/ interference ratios in receivers but the spacing among the antenna elements are typically required to be around half wavelength to avoid mutual coupling. Closely spaced (d<0.1λ) antenna elements with multiport matching networks can overcome the mutual coupling at the price of reduced impedance matching bandwidth. In this paper, 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 that approaches to 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 a signal to noise ratio improvement that is consistent with the theoretical prediction. The proposed approach avoids to the loss and complexity of using multiport matching networks yet can achieve a signal to noise ratio gain over a broad bandwidth. It may find applications in wireless sensing that demands high sensitivity from antenna arrays in small form factors.