Fano Resonances of a Multi-Slot Iris in a Circular Waveguide

Fano resonances of a multi-slot iris in a circular waveguide are analyzed using both numerical simulations based on the mode-matching technique and eigenoscillation analysis. Three scenarios that produce characteristic asymmetric frequency responses are investigated: (1) the excitation of high-Q antisymmetric oscillation on the background of a low-Q symmetric oscillation due to structural asymmetry; (2) the appearance of Fano resonances in a symmetric three-slot iris associated with antiphase field distributions; and (3) the transformation of a Fano-type singlet into a Lorentz-type reflection resonance in irises with a large central aperture. The results reveal how the coupling of eigenoscillations leads to complete transmission and reflection resonances, enabling the design of highly selective reflection cells in circular waveguides.