Design of fixed- and varactor-tuned bandstop filters with spurious suppression

A new spurious suppression method for bandstop filters based on constructive interference is presented. The technique is successfully applied to realize a fixed-tuned filter with an upper passband extending more than 9 times the fundamental bandstop response, as well as a varactor-tuned bandstop filter with an upper passband extending to 8.9 times the fundamental.