Insights into the electromagnetic properties of the resonant slow-wave circuits from the resonant cavity perspective

A multigap resonant cavity can simply be regarded as either a slow-wave structure (SWS) with shorted ends or as a resonator. However, two distinct physical images will be obtained when characterizing the electromagnetic properties of such circuits. In particular, dispersion is no longer a necessary concept from the resonant cavity perspective. The periodicity of the circuit and the synchronization characteristics with the beam are incorporated in the longitudinal electric field shape. Thus, we present insights from the resonant cavity perspective by taking the resonant rectangular grating SWS as an example. It is found that even if the fields are originally expressed as normal modes, they can be transformed into the space harmonic form. This is thought to be the result of the periodicity of the circuit, which provides a connection between the multigap resonant cavity and the SWS. We present the findings and discuss their physical significance.