Circularly Polarized 2-D MIMO Radar System Using Scalable Aperture Shared Array for IoT Radar Imaging

This paper presents a 24 GHz circularly polarized (CP) two-dimensional (2D) MIMO FMCW radar front-end based on a scalable aperture-shared array for compact IoT radar imaging. The key contribution is an aperture-shared CP architecture that enables dense Tx/Rx integration within a compact footprint, addressing a fundamental limitation of conventional 2D MIMO radars in which improving angular sensing efficiency under a size-constrained aperture typically requires a larger physical aperture and therefore results in poor spatial efficiency for compact platforms. The proposed design implements a shared-aperture tile that integrates 2 TX and 4 RX channels within a 2.0λ0 × 2.0λ0 aperture, while preserving wide 2D angular coverage and practically sufficient angular discrimination for volumetric sensing tasks relevant to IoT applications. High-isolation operation under dense aperture sharing is achieved through a co-aperture CP antenna structure incorporating a defected ground structure (DGS), which maintains radiation integrity and mitigates Tx-to-Rx leakage and coupling. The proposed architecture also supports scalable tiling of identical aperture-shared tiles to extend the effective 2D aperture while preserving a compact per-tile footprint. The proposed radar is validated through an end-to-end hardware prototype with simulations and measurements, demonstrating reliable multi-target separation and two-dimensional imaging capability.