A Dual-Slant-Polarized In-band Full-duplex (IBFD) Antenna System with Four Isolated Channels

An in-band full-duplex (IBFD) antenna system having four ports with good self-interference cancellation (SIC) is presented in this paper. Two of the four ports provide +45-degree-polarized radiation and the other two generate -45 degree-polarized radiation. To achieve high isolation between any two of the four ports, three types of coupling need to be suppressed simultaneously, which are the cross-polarization coupling between the two ports of the same antenna, the co-polarization coupling between adjacent antennas, and the crosspolarization coupling between adjacent antennas. The three types of couplings are defined as A-type, B-type, and C-type coupling, respectively. In this work, a novel isolation feed network is firstly proposed to deal with A coupling. The isolation feed network also can differentially feed the antenna and achieve 45-degree polarizations without rotating the antenna. Then, the B- and C-couplings are also well suppressed in a double-antenna system thanks to the extra defected ground structure (DGS), cross-shaped walls, and metal baffles. The resultant isolation between any two of the four ports is > 39 dB from 3.3 to 3.9 GHz. The radiation patterns obtained by exciting the four ports are very similar to each other and are stable with frequency, which makes the proposed antenna an excellent candidate for 5G sub-6 GHz IBFD applications.