Ultra wide pass-band, absorptive band-reject filter

摘要

An ultra wide band-pass, absorptive band-reject filter has a pair of quadrature hybrid couplers cascaded and coupled by a phase shifting element and a matched pair of band-reject filters in two parallel paths. The matched pair of band-reject filters each rejects signals in a desired reject frequency band. The quadrature hybrid couplers each have an insertion loss amplitude crossover for signals propagated to terminals across the coupler that coincides with the reject frequency band. The phase shifting element is configured to have a phase shift of 180 degrees at frequencies in the reject frequency band. In a preferred embodiment, the pair of quadrature hybrid couplers are identical in performance and the band-reject filters are identical in performance with respect to a center frequency fn of the reject frequency band. The absorptive band-reject filter thereby provides an absorptive rejection response in the reject frequency band while a very wide pass-band frequency range is maintained.