Study of a folded resonator including the effects of higher order modes

This paper presents a derivation of the 2-port matrix for a folded quarter-wave side-branch resonator including higher order modes but neglecting flow interaction effects. The model is restricted to coaxial geometries and two-folds. The derivation is based on the mode matching technique and is verified by measurements done on prototypes. A notable result from these experiments is the effects of a slit-like leakage close to a rigid wall. A parametrical study finally investigates the influence of various lengths and area ratios of the resonator resulting in a set of design rules.