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.