a variable q reflection mode filter has a three - port circulator , one port of which is terminated by a one - port filter . the filter includes a ladder network of resonators , successive of the resonators having progressively reducing q values . the filter increases the overall 3 db resonance point of the filter to reduce the unloaded q factors required for particular applications . the filter may be arranged to provide a maximally flat response , an equiripple response , or a quasi - ripple response . transmission zeros may also be incorporated to further enhance the effective unloaded q .