A triple-passband filter with doubly coupled hairpin TSIRs

In order to obtain triple-passband filters with much wider fractional bandwidth, a doubly coupled structure with tri-section stepped-impedance resonators(TSIR) in each coupling path is proposed in this paper. This structure has the advantages of a much wider fractional bandwidth in the higher passbands without sacrificing the passband´s insertion losses. To verify the design concept, a 1.0/2.4/3.6GHz triple-passband microstrip filter has been fabricated and measured, It is shown that the measured and simulated performance are in good agreement.