Resonant Modes of Disk-Loaded Cylindrical Structures With Open Boundaries

Disc-loaded cylindrical structures are found in many microwave devices and components, which in some cases need to be studied as open resonators. The electromagnetic formulation and analysis presented involves the use of a generalized mode-matching technique that expands the fields as eigenmodes in the longitudinal direction. This method allows one to model disc-loaded geometries with partial dielectric loading and is also much more efficient for overmoded structures than a transverse expansion of the fields. In addition, the method is extended to the complex plane of frequencies, where the resonant modes are found from the numerical search for zeros of a complex determinant. A numerical code is developed, and after comparing the results to those from a commercial code, it is used to study some characteristic cases. The calculated results include resonant frequencies, quality factors, and field profiles of resonant modes with diffraction and dielectric losses.