The impact of coupling on the reflections of cavity resonators

The coupling to filters can have a major impact on the reflected signal, especially on the phase, and therefore represents an important parameter. In this paper the impact of the coupling on the circuit parameters of a circular cavity filter is investigated. Capacitive and inductive coupling are considered and their properties are compared. An equivalent circuit model was used to determine the parameters of the measured and simulated data and to explain the effects. To account for the demand of broadband models, the circuit model has been expanded to take higher order resonances with different coupling polarities into account. Finally the model is validated by fitting it to broadband measurement data.