Antenna-Duplexed Passive Beamforming Front-end for Joint Communication and Sensing

Wide scale deployment of wireless devices is making the spectrum a scarce resource. Joint communication and sensing (JC&S) and in-band full duplex (IBFD) communications provide opportunities of spectrum reuse. IBFD communication hardware requires high transmitter-to-receiver (TRx) isolation, making it shareable and reusable with mono-static continuous wave radar in JC&S context. On the other hand, design and development of beamforming phased arrays, required for communication coverage and radar spatial filtering, becomes challenging when a high TRx isolation assurance is required. This paper presents a solution in the form of antenna-duplexed passive beamformer usable for IBFD communication and mono-static continuous wave radars, mitigating two key challenges/requirements of JC&S hardware reuse in co-design approach - TRx isolation and beamforming capability. A beamformer using Butler matrix and a planar quasi-circulator are designed and optimized for X-band (centered at 10 GHz) providing up to 40 dB transmitter leakage suppression using primarily passive circuits.