A Four-Port Shared-Aperture In-Band Full-Duplex Antenna Array Based on a Novel Common-Mode and Differential-Mode Combination Method

In this paper, a four-port shared-aperture in-band full-duplex (IBFD) antenna system is developed based on a novel common-mode (CM) / differential-mode (DM) combination method. By combining the CM and DM of two dual-polarized subarrays, each port of the antenna system excites the entire aperture of the antenna array, leading to the improved gain while maintaining the half-power beamwidth (HPBW) at around 70 degrees. Besides, the intrinsic orthogonality of the two modes leads to low coupling between ports. To verify the proposed method, an IBFD array system, which consists of three modules including differential-fed antenna array, hybrid couplers and power dividers, is designed, fabricated, and measured to realize the sharedaperture excitation from the four ports. Differential feed and decoupling structures are employed to further increase the isolation between ports, which is greater than 38 dB within the bandwidth of 3.3 - 3.8 GHz (14.1%). The gains of all four ports are greater than 8 dBi with more than 20 dB cross-polarization discrimination (XPD). The simulation and experimental results demonstrate great potential of this work in the 5G and beyond sub-6 GHz IBFD systems.