Abstract: A novel full-wave hybrid technique was formulated to treat three-dimensional discontinuities in isotropic chiral materials present in rectangular waveguides with perfect electrically conducting walls. Our formulation comprises (i) the coupled-mode method for obtaining the electromagnetic field in each section that is homogeneous in the propagation direction and (ii) the mode-matching method for obtaining the generalised scattering matrix of each discontinuity (formed by two adjacent homogeneous sections). In particular, we reformulated the coupled-mode method based on appropriate representations of E and B. This formulation ensures the satisfaction of the boundary conditions of the magnetic field on perfect electrically conducting walls, which is not ensured by the conventional formulation of the coupled-mode method as it is based on representations of E and H. A new expansion for H emerges indirectly from our formulation. Knowledge of this expansion is required by the mode-matching method for incorporating the effects of discontinuities between adjacent homogeneous sections. Calculations confirmed that our new formulation delivers correct results, whereas the conventional formulation may not.

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