Self-Interference Mitigation in In-Band Full-Duplex Systems Using 180° Hybrid Coupler for 5G Application

In-band full duplex (IBFD) system is an evolving technology in communications, however its implementation is often susceptible to interference. Therefore, this paper proposes to enhance the performance of IBFD system, particularly in the context of fifth-generation (5G) application which is operating within the frequency of 3.5 GHz. By utilizing a Self-Interference Cancellation (SIC) technique, the capability in interference mitigation is investigated by implementing a 180° hybrid coupler on an IBFD antenna integrated with a proximity coupling method. The results show a good performance of refection coefficient on Port $1\left(\mathrm{~S}_{11}\right)$ at the desirable frequency, satisfying predefined standard with the value of less than –10 dB. Moreover, the performance of reflection coefficient on Port $2\left(\mathbf{S}_{22}\right)$ adheres closely to the specified requirement, surpassing the measured value which exceeds $\mathbf{- 1 0} \mathrm{dB}$. In addition, the results also highlight the effective isolation which is characterized by polarization tendencies converging towards directional behavior, thus affirming its suitability for 5G application.