A Compact Co-Linearly Polarized Full-Duplex Patch Antenna With High Isolation and Broadside Symmetrical Radiation Pattern for Integrated Sensing and Communication in IoT

This article innovatively presents a compact co-linearly polarized (LP) full-duplex patch antenna that exhibits high isolation and broadside symmetrical radiation pattern at the ISM band for integrated sensing and communication (ISAC) in Internet of Things (IoT). The design features an extremely closely spaced Tx-Rx antenna pair with an edge-to-edge distance of 0.5 mm ( $0.009~\lambda _{0}$ ), aiming at mitigating radiation pattern misalignment. Additionally, a novel decoupling structure is proposed, incorporating a center-connecting-strip with a grounding-through-via positioned at the antenna’s midpoint, effectively canceling both port coupling and radiation pattern interference. A thorough analysis is conducted from current distribution, equivalent circuit modeling, and characteristic mode theory to provide deeper physical insights and elucidate the decoupling mechanism. Both simulations and measurements of the prototype are performed to validate the design approach. Experimental results prove that the proposed full-duplex antenna demonstrates possesses the merits of high Tx-Rx isolation (a maximum value of 61.6 dB), compact size ( $0.07~\lambda _{0}^{3}$ ), straightforward decoupling and feeding scheme, broadside and symmetrical radiation patterns (a maximum 3-dB beamwidth of 103°). Moreover, extensive full-duplex system validations for both wireless communication and radar sensing are conducted by integrating the proposed antenna into a custom-designed radar system. These validations confirm the merits of the antenna’s high isolation and wide beamwidth in practical system applications, thereby not only validating the effectiveness of the decoupling strategy but also showcasing the potential of the antenna for ISAC applications in IoT era.