Resonance Lineshapes in Quasi-One-Dimensional Scattering

An S matrix approach is developed to describe elastic scattering resonances of systems where the scattered particle is asymptotically confined and the scattering potential lacks continuous symmetry. Examples are conductance resonances in microstructures or transmission resonances in waveguide junctions. The generic resonance is shown to have the asymmetric Fano lineshape. The asymmetry parameter q is independent of coupling to the quasi-bound level implying a scaling property of the resonances which can be tested in transport experiments.