An Inductive Decoupling Approach for High Isolation in Compact Copolarized Planar In-Band Full Duplex Antenna

This letter presents the design of a simple, compact, copolarized antenna with high isolation. The complete configuration consists of two quarter patch antennas interconnected by an inductive decoupling structure (combination of simple transmission line and a via). The stop-band phenomena of the decoupling structure are validated through an equivalent circuit model. The proposed technique is verified for both symmetric and antisymmetric port configurations. Furthermore, adding an air gap between the two substrates enhances the operating bandwidth (BW). Experimental results demonstrate a maximum 77 dB isolation with a 2.2% BW for the original structure and 70 dB isolation with 4.5% BW for the structure with an air gap. Therefore, the proposed configuration exhibits great potential for copolarized, highly isolated, and compact in-band full duplex antennas that are suitable for 5G and 6G applications.