Nonorthogonal Polarized MIMO Antenna for Simultaneous Transmit and Receive in Wi-Fi-Based Integrated Sensing and Communication

Simultaneously suppressing self-interference (SI), crosstalk interference (XI), and multiple-input-multiple-output (MIMO) interference over a wideband presents significant challenges in a simultaneous transmit and receive (STAR) MIMO antenna. This article presents a $2\times 2$ STAR MIMO antenna that utilizes a usual stacked patch array while effectively suppressing all three types of interferences throughout the 5-GHz Wi-Fi spectrum. Moreover, these interference suppressions are accomplished when the TX-RX polarization of this antenna is nonorthogonal within one channel and between channels at the same time. In this work, a circularly polarization-linearly polarization (CP-LP) scheme with a broadband coupling adjustment (BCA) approach is proposed to minimize SI by producing wideband cancellation between residual TX-to-RX couplings. Metal walls with slot structures on the ground were designed to prevent interferences between channels while preserving antenna impedance matching. A prototype of the nonorthogonal polarized STAR MIMO antenna was constructed, showing good agreement between simulation and measurement. At $5.1\sim 5.85$ GHz, it simultaneously suppresses all three interferences below –40 dB, with peak gains exceeding 7 dBic for TX and 8.7 dBi for RX, making this antenna promising for Wi-Fi-based integrated sensing and communication (ISAC).