Design of an RF Component for In-Band Full-Duplex Systems

This work explores the design, optimization, and practical implementation of an advanced rat-race coupler with enhanced bandwidth and isolation performances for self-interference cancellation (SIC) in in-band full-duplex systems. The component is positioned at the antenna interface to effectively mitigate the self-interference signal from the received signal, exploiting the inherent signal-processing properties of the component. To address these challenges, the novel approach proposed consists of the implementation of Chebyshev multi-section transformers in the component structure, with an improvement of 30\% in operative bandwidth and doubling the isolation bandwidth. This thesis starts with a comprehensive theoretical analysis of the 180-hybrid coupler, with particular emphasis on even and odd mode analysis and the delicate amplitude and phase balance needed for optimal isolation. The proposed structure is validated both with schematic and EM full-wave simulations using Keysight Advanced Design System (ADS). The optimized microstrip implementation is finally realized on a Rogers RO4003C substrate and measured, demonstrating a superior isolation level and bandwidth with respect to a conventional structure. This work contributes to advancing the SIC capabilities at the antenna interface by relying on passive components only. The proposed solution reduces the dependence on complex active cancellation techniques, supporting the goal of reducing the self-interference signal and enabling IBFD communication for next-generation wireless technologies.