Enabling Near-Field Sensing via Extremely Large Antenna Spacing

Abstract

This paper introduces an extremely large antenna spacing (ELAS) architecture for monostatic multiple-input multiple-output (MIMO) sensing that enables effective near-field (NF) operation over radar-relevant ranges while reducing hardware complexity. The transmitter employs a uniform linear array (ULA) with conventional half-wavelength inter-element spacing and low-complexity far-field (FF) beam steering. Conversely, the receiver uses a small number of widely spaced elements to achieve a large effective aperture, thereby inducing an NF operating regime. We derive closed-form NF range–angle characteristics and show that, with proper array design, grating lobes caused by sparse spatial sampling of the receive aperture can be mitigated in the composite transmit–receive response. Numerical results demonstrate that effective NF operation over a large sensing extent can be achieved with a substantially reduced antenna count compared to half-wavelength arrays.