Compact In-Band Full Duplexing Antenna for Sub-6 GHz 5G Applications

A novel compact in-band full duplexing antenna using a cavity-like structure for sub-6 GHz fifth-generation (5G) applications is proposed. By exploring a shared aperture cavity-like structure with two highly orthogonal modes (quarter-wavelength slot mode and half-mode cavity mode), high isolation between Tx and Rx ports is achieved. Two quarter-wavelength slots are etched on both sides of the cavity, so a shared aperture dual-mode cavity is implemented. When this cavity is fed by a pair of even–odd mode feeding structures, two orthogonal polarization modes are excited at the same frequency band. To validate the proposed concepts, a high isolation duplexing antenna with a compact size of 0.45 λ
₀
× 0.20 λ
₀
× 0.04 λ
₀
is fabricated. A measured isolation greater than 43 dB is achieved over the working band from 3.4 to 3.8 GHz (LTE B42/B43 band) and its peak radiation efficiency is larger than 87%. It shows a compact size, low cost, high isolation, good bandwidth, and efficiency, which is well situated for in-band duplexing systems and 5G indoor application.