Orthogonal Coded Active Illumination for Millimeter Wave, Massive-MIMO Computational Imaging With Metasurface Antennas

Emerging metasurface antenna technology enables flexible and low cost massive multiple-input multiple-output (MIMO) millimeter-wave (mmW) imaging for applications such as personnel screening, weapon detection, reconnaissance, and remote sensing. This work proposes an orthogonal coded active illumination (OCAI) approach which utilizes simultaneous, mutually orthogonal coded transmit signals to illuminate the scene being imaged. It is shown that OCAI is robust to code amplitude and code phase imbalance introduced by imperfect transmitter (TX) and receiver (RX) hardware, while also mitigating common impairments of low cost direct-conversion receivers, such as RX self-jamming and DC offsets. The coding gain offered by this approach improves imager signal to noise ratio performance by up to 15 dB using codes of symbol length 32. We present validation images of resolution targets and a human-scale mannequin, obtained with a custom massive-MIMO mmW imager having 24 simultaneous TXs and 72 simultaneous RXs operating in the K-band (17.5 GHz to 26.5 GHz). The imager leverages both spatial coding via frequency diverse metasurface antennas, and temporal coding via OCAI of the scene.