A Four-Channel In-Band Full-Duplex (IBFD) Antenna System with Shared Radiation Aperture

A four-channel in-band full-duplex (IBFD) antenna array system with shared radiation aperture based on common-mode (CM) and differential-mode (DM) combination is developed in this paper. The antenna system consists of two subarrays. Exciting any of the four input ports simultaneously excites one subarray in CM and the other subarray in DM. The inclusion of both CM and DM in both the
$\boldsymbol{xoz}$
and
$\boldsymbol{yoz}$
planes leads to identical radiation patterns when any of the four ports are excited. The IBFD antenna system was designed, fabricated, and measured to verify the effectiveness of the method. The isolation between any two ports is >38 dB within the bandwidth of 3.3 - 3.8 GHz (14.4%). The gains of all four ports are > 8 dBi with large cross-polarization discrimination (XPD) > 20 dB. Moreover, each port of the system exhibits similar and broadside radiation patterns in both the
$\boldsymbol{xoz}$
and
$\boldsymbol{yoz}-\mathbf{planes}$
, which demonstrates the excellent potential of this work for IBFD systems in 5G sub-6 GHz applications.