A bandstop filter configured to suppress a spurious resonance frequency includes a resonator and a transmission line that is coupled to the resonator at a first junction and at a second junction with a length θ of transmission line running between the two couplings. The configuration provides two signal paths so that constructive interference occurs at the spurious resonance, and destructive interference occurs at a fundamental bandstop frequency. This provides spurious suppression by effectively cancelling out resonator couplings via the constructive interference, extending the upper passband of the bandstop filter to any degree required by the application.