In this thesis, the bandstop filter (BSF) topologies for bandstop-to-bandpass reconfigurable filters are presented. The conventional BSF topologies which do not contain the inter-resonator couplings are not suitable to realize the bandpass responses. The couplings between resonators are inevitable to realize the bandpass responses. Therefore, the new BSF topologies possessing the inter-resonator couplings are proposed for the 3rd-order and 4th-order BSF designs.
The coupling coefficient relationships between the conventional and the proposed BSF topologies are derived by comparing the transmission coefficients of both topologies. Based on the relationships, the frequency responses of the proposed BSF topologies can be identical to those of the conventional ones even though two BSF topologies have different coupling coefficients; beside, the coupling coefficients for the proposed topologies can be analytically extracted from the well-known coupling coefficients of the conventional topologies. 3rd-order and 4th-order BSFs utilizing both topologies are designed and manufactured to verify the theories using substrate integrated cavity (SIC) type resonators.
The proposed 3rd-order BSF topology is applied to realize a bandstop-to-bandpass reconfigurable filter with switching elements. The presented reconfigurable filter can exhibit a bandstop or a bandpass response at the same operating frequency depending on the state of the switching elements. The frequency tunable SIC resonators are used to construct the reconfigurable filter and the operating frequency can be tuned using frequency tuning elements. The design procedures, fabrications, and experimental results for the BSF topologies and the bandstop-to-bandpass reconfigurable filter are demonstrated in this thesis.